Quadrantid meteors on January 3 or 4

Tonight, a possible meteor shower? The annual Quadrantid shower comes every year at this time. It’s nominally active during the first week of January and best seen from Earth’s northerly latitudes. However, peak activity lasts less than a day, and you need to be on Earth’s night side during the Quadrantids’ short peak. Who will see the shower in 2017? Hard to say. Different sources sometimes list different peak times for meteor showers. For the 2017 Quadrantids, we’re finding some agreement that the peak is due Tuesday, January 3 at 15 hours UTC; translate to your time zone here.

If the peak does occur then, the Americas will have better luck on the morning of January 3. Those in Asia should try the hours after midnight on the morning of January 4.

For all of us, some good new. In 2017, the waxing crescent moon will leave the sky during the evening hours. For all of us, the hours between midnight and dawn (either January 3 or 4) will be best.

Will you see any meteors? Maybe!

You wouldn’t think people would be so determined to watch such an iffy shower. The Quadrantid shower has such a narrow peak, lasting for only a few hours. If you miss the peak – which is easy to do – you won’t see many meteors.

But the pay-off can be good! The Quadrantids can match the meteor rates of the better-known August Perseid and December Geminid showers. The shower has been known to produce up to 50-100 or more meteors per hour in a dark sky.

Just know that this meteor shower favors the Northern Hemisphere because its radiant point – the point in the sky from which the meteors appear to radiate – is far to the north on the sky’s dome. So it’s not a globally watched shower, as many are.

If you’re thinking of watching the Quadrantids, do it. Meteor shower peaks are rarely a certainty. It’s nearly always a gamble that a shower will reward you with a good show.

These almanacs can help you find moonrise times for your sky

The Quadrantid shower is named after the defunct 19th century constellation Quadrans Muralis. If you trace the paths of the Quandrantids backward, they appear to radiate from a point where this constellation once reigned in the sky. If you wish, you can locate the Quadrantid radiant in reference to the Big Dipper and the bright star Arcturus. Use the chart at the top of this post.

But you don’t need to find the radiant to enjoy the Quadrantids. You only need a dark, open sky for an hour or so before dawn.

View larger. | EarthSky Facebook friend Susan Jensen caught this beautiful Quadrantid in 2013.

Bottom line: If you’re at a northerly latitude, try the Quadrantid meteor shower from late night January 2 to dawn January 3, 2017. If you don’t see any meteors, try from late night January 3 to dawn January 4. This shower can produce 50-100 meteors per hour, but its peak is short and sweet.

Want more? Try this post. Everything you need to know: Quadrantid meteor shower

Never miss another full moon! EarthSky moon calendar for 2017

EarthSky’s meteor shower guide for 2017

Big and Little Dippers: Noticeable in northern sky

from EarthSky http://ift.tt/1wEBULd

Tonight, a possible meteor shower? The annual Quadrantid shower comes every year at this time. It’s nominally active during the first week of January and best seen from Earth’s northerly latitudes. However, peak activity lasts less than a day, and you need to be on Earth’s night side during the Quadrantids’ short peak. Who will see the shower in 2017? Hard to say. Different sources sometimes list different peak times for meteor showers. For the 2017 Quadrantids, we’re finding some agreement that the peak is due Tuesday, January 3 at 15 hours UTC; translate to your time zone here.

If the peak does occur then, the Americas will have better luck on the morning of January 3. Those in Asia should try the hours after midnight on the morning of January 4.

For all of us, some good new. In 2017, the waxing crescent moon will leave the sky during the evening hours. For all of us, the hours between midnight and dawn (either January 3 or 4) will be best.

Will you see any meteors? Maybe!

You wouldn’t think people would be so determined to watch such an iffy shower. The Quadrantid shower has such a narrow peak, lasting for only a few hours. If you miss the peak – which is easy to do – you won’t see many meteors.

But the pay-off can be good! The Quadrantids can match the meteor rates of the better-known August Perseid and December Geminid showers. The shower has been known to produce up to 50-100 or more meteors per hour in a dark sky.

Just know that this meteor shower favors the Northern Hemisphere because its radiant point – the point in the sky from which the meteors appear to radiate – is far to the north on the sky’s dome. So it’s not a globally watched shower, as many are.

If you’re thinking of watching the Quadrantids, do it. Meteor shower peaks are rarely a certainty. It’s nearly always a gamble that a shower will reward you with a good show.

These almanacs can help you find moonrise times for your sky

The Quadrantid shower is named after the defunct 19th century constellation Quadrans Muralis. If you trace the paths of the Quandrantids backward, they appear to radiate from a point where this constellation once reigned in the sky. If you wish, you can locate the Quadrantid radiant in reference to the Big Dipper and the bright star Arcturus. Use the chart at the top of this post.

But you don’t need to find the radiant to enjoy the Quadrantids. You only need a dark, open sky for an hour or so before dawn.

View larger. | EarthSky Facebook friend Susan Jensen caught this beautiful Quadrantid in 2013.

Bottom line: If you’re at a northerly latitude, try the Quadrantid meteor shower from late night January 2 to dawn January 3, 2017. If you don’t see any meteors, try from late night January 3 to dawn January 4. This shower can produce 50-100 meteors per hour, but its peak is short and sweet.

Want more? Try this post. Everything you need to know: Quadrantid meteor shower

Never miss another full moon! EarthSky moon calendar for 2017

EarthSky’s meteor shower guide for 2017

Big and Little Dippers: Noticeable in northern sky

from EarthSky http://ift.tt/1wEBULd

January guide to the bright planets

If you look westward after sunset, you’ll easily see a very bright starlike object. That’s the planet Venus. Mars is nearby. The moon is sweeping past these planets on the first few evenings of 2017. Read more about the moon and planets. There’s also a very faint comet in that part of the sky. Read more about the comet.

Two of the five bright planets rise to great prominence in January 2017 sky. Venus rules over the evening sky whereas Jupiter lords over the morning sky. Venus, the brightest planet, blazes in the west first thing at dusk, and reaches its greatest elongation as the “evening star” on January 12. Jupiter, the second-brightest planet, lords over the eastern half of sky between midnight and sunrise. Mars joins Venus in the evening sky, though it’s higher up and much fainter than Venus, setting in the west shortly after Venus does. Venus and Mars remain close together on the sky’s dome throughout January, whereas Saturn appears in the southeastern predawn/dawn sky. Seek for Mercury a short hop beneath Saturn, just as darkness is giving way to morning twilight. Follow the links below to learn more about planets in January 2017.

Brilliant Venus is the “evening star”

Mars, east of Venus, until mid-evening

Saturn returns to the morning sky

Bright Jupiter lords over morning sky

Mercury in the morning sky

Like what EarthSky offers? Sign up for our free daily newsletter today!

Astronomy events, star parties, festivals, workshops

Visit a new EarthSky feature – Best Places to Stargaze – and add your fav.

Skywatcher, by Predrag Agatonovic.

Watch for the waxing crescent moon to go by the planets Venus and Mars in early January 2017. Read more.

Brilliant Venus is the “evening star.” Okay, it’s not a star. It’s a planet. But people will call it the evening star all the same. In these past weeks, many have noticed Venus and been amazed at its brilliance in the west after sunset. It’s the brightest planet and very, very bright, to reach its greatest evening elongation on January 12.

Be sure to catch the waxing crescent moon near Venus in early January, as displayed on the sky chart above. Click here for details.

Watch for Venus to close the gap between itself and Mars. These two visible evening planets will be closer together on the sky’s dome by the month’s end and closer yet in early February 2017.

From mid-northern latitudes (U.S. and Europe), Venus sets about four hours after the sun throughout the month.

At mid-southern latitudes (Australia and South Africa), Venus sets about about three hours after the sun in early January and about 2.5 hours after sun by the month’s end.

Mars, east of Venus, until mid-evening. After appearing as a bright red light in our sky last May and June 2016, Mars now appears only modestly bright (though possibly still ruddy), above dazzling Venus. Venus is so bright that it pops out almost immediately after sunset, but you’ll have to wait until nightfall to see fainter Mars. Look for the moon close to Mars for a few evenings, on or near January 2 or 3.

From mid-northern latitudes (U.S. and Europe), look for the red planet Mars to set in the west around 9 to 10 p.m. all month long.

At mid-southern latitudes (Australia and South Africa), Mars sets in the west around 9 to 10 p.m. (10 to 11 p.m. summer time).

Mars will linger in our sky for several more months. Keep in mind, however, that Earth is traveling away from Mars as we speak – moving far ahead of this planet in the endless race around the sun – so Mars is dimming in our evening sky. Mars is in its long, lingering, relatively inconspicuous phase now. It’ll be still visible in the west to the unaided eye – though not prominent – during its conjunction with Uranus on the evening of February 27, 2017.

Mars won’t make its transition from the evening to morning sky until July 27, 2017. Even so, Mars’ stature in the evening sky will continue to diminish to that of a rather faint “star,” and we expect few – if any – skywatchers to observe the conjunction of Mars and Mercury in the evening sky on June 28, 2017.

The conjunction of Mars and Venus in the morning sky on October 5, 2017, may well present the first good opportunity to spot Mars in the morning sky when it returns from being behind the sun on July 27, 2017.

Looking for a sky almanac? EarthSky recommends…

View larger | Mikhail Chubarets in the Ukraine made this chart. It shows the view of Mars through a telescope in 2016. We never see Mars as a disk like this with the eye alone. But you can see why Mars was bright to the eye in 2016, and is now fading.

Watch for the moon to meet up with Saturn on or near Janaury 24, 2017. Read more.

Saturn returns to the morning sky. Saturn swung behind the sun on December 10, 2016, transitioning from the evening to morning sky.

In both the Northern and Southern Hemispheres, Saturn returned to the morning sky in late December 2016. In early January, Saturn rises in the east about two hours before the sun, and by the month’s end, Saturn comes up several hours before sunrise. Be sure to let the waning crescent moon guide you to Saturn (and the nearby star Antares) for several days, centered on or near January 24.

Saturn, the farthest world that you can easily view with the eye alone, appears golden in color. It shines with a steady light.

Binoculars don’t reveal Saturn’s gorgeous rings, by the way, although binoculars will enhance Saturn’s golden color. To see the rings, you need a small telescope. A telescope will also reveal one or more of Saturn’s many moons, most notably Titan.

Saturn’s rings are inclined at nearly 27^o from edge-on, exhibiting their northern face. In October 2017, the rings will open most widely, displaying a maximum inclination of 27^o.

As with so much in space (and on Earth), the appearance of Saturn’s rings from Earth is cyclical. In the year 2025, the rings will appear edge-on as seen from Earth. After that, we’ll begin to see the south side of Saturn’s rings, to increase to a maximum inclination of 27^o by May 2032.

Click here for recommended almanacs. They can help you know when the planets rise, transit and set in your sky

Tom Wildoner over-exposed Saturn itself to capture this view of Saturn’s moons on June 25, 2016. Visit Tom at LeisurelyScientist.com.

Contrasting the size of Saturn and its rings with our planet Earth via Hubble Heritage Team.

The moon swings by the planet Jupiter and the star Spica for several days, centered on or near January 19, 2017. .

Bright Jupiter lords over the morning sky. Jupiter’s increasing prominence as the “morning star” will be hard to overlook. To see Jupiter, seek out the brightest starlike object in the predawn sky or the morning twilight and that’ll be the king planet Jupiter! Jupiter rises in the east at late night and soars to its highest point in the sky at or near dawn.

From mid-northern latitudes, like those in the U.S. and Europe, Jupiter rises around one hour after the midnight hour in early January. By the month’s end, Jupiter rises roughly one hour before midnight.

From mid-southern latitudes (Australia), look for Jupiter to rise around midnight in early January and about two hours before midnight by the end of the month.

If you’re not a night owl, your best bet for catching Jupiter is to wake up before sunrise to see this brilliant beauty of a planet lighting up the predawn and dawn sky. Watch for the waning moon to join up with Jupiter for several days, centered on or near January 19. See the above sky chart.

By the way, Jupiter shines in front of the constellation Virgo, near Virgo’s brightest star, Spica. Jupiter serves a great reference for learning the constellations of the zodiac, because Jupiter stays in each constellation for roughly a year. So use Jupiter to become familiar with the star Spica and the constellation Virgo, starting now, and throughout 2017.

If you have binoculars or a telescope, it’s fairly easy to see Jupiter’s four major moons, which look like pinpricks of light on or near the same plane. They are often called the Galilean moons to honor Galileo, who discovered these great Jovian moons in 1610. In their order from Jupiter, these moons are Io, Europa, Ganymede and Callisto.

Jupiter and its four major moons via Jan Sandberg

These moons circle Jupiter around the Jovian equator. In cycles of six years, we view Jupiter’s equator edge-on. So, in 2015, we got to view a number of mutual events involving Jupiter’s moons through a high-powered telescope. Click here or here or here for more details.

Although Jupiter’s axial tilt is only 3^o out of perpendicular relative to the ecliptic (Earth’s orbital plane), Jupiter’s axis will tilt enough toward the sun and Earth so that the farthest of these four moons, Callisto, will NOT pass in front of Jupiter or behind Jupiter for a period of about three years, starting in late 2016. During this approximate 3-year period, Callisto will remain “perpetually” visible, alternately swinging “above” and “below” Jupiter.

Click here for a Jupiter’s moons almanac, courtesy of Sky & Telescope.

Eliot Herman in Tucson, Arizona caught Mercury on the night of December 11, 2016, amidst crepuscular rays from the setting sun.

Look for the thin waning crescent moon and the planet Mercury low in the sky as the predawn darkness gives way to dawn. Who knows? Someone might even catch the moon below Mercury on January 26! The green line depicts the ecliptic – Earth’s orbital plane projected on the sky. Read more.

Mercury in the morning sky. Mercury transitioned from the evening to morning sky on December 28, 2016. This month, beginning in the second week of January 2017, Mercury should climb far enough from the glare of sunrise to become visible in the morning sky from both the Northern Hemisphere and the Southern Hemisphere. Saturn rises before Mercury does, so use Saturn as your guide “star” to locating Mercury closer to the horizon.

Try viewing Mercury before sunrise for a few weeks, centered on Mercury’s greatest morning elongation on January 19. Mercury is tricky. If you look too soon, Mercury will be lost in the twilight glare; if you look too late, it will have followed the sun beneath the horizon. Watch for Mercury low in the sky, and near the sunrise point on the horizon, seeking for this hidden treasure around 90 to 60 minutes before sunrise. Remember, binoculars are always helpful for any Mercury search. Good Luck!

For a big challenge, seek for the slender waning crescent moon pairing up with Mercury before sunrise on January 25 and 26. Binoculars may come in handy!

Click here for recommended almanacs; they can give you Mercury’s rising time in your sky.

What do we mean by bright planet? By bright planet, we mean any solar system planet that is easily visible without an optical aid and that has been watched by our ancestors since time immemorial. In their outward order from the sun, the five bright planets are Mercury, Venus, Mars, Jupiter and Saturn. These planets actually do appear bright in our sky. They are typically as bright as – or brighter than – the brightest stars. Plus, these relatively nearby worlds tend to shine with a steadier light than the distant, twinkling stars. You can spot them, and come to know them as faithful friends, if you try.

From late January, and through mid-February, 5 bright planets were visible at once in the predawn sky. This image is from February 8, 2016. It’s by Eliot Herman in Tucson, Arizona. View on Flickr.

Bottom line: In January 2017, two of the five bright planets appear in the evening sky at dusk/nightfall: Venus and Mars. The other three planets – Jupiter, Saturn and Mercury – are found in the morning sky.

Easily locate stars and constellations with EarthSky’s planisphere.

Don’t miss anything. Subscribe to EarthSky News by email

from EarthSky http://ift.tt/IJfHCr

If you look westward after sunset, you’ll easily see a very bright starlike object. That’s the planet Venus. Mars is nearby. The moon is sweeping past these planets on the first few evenings of 2017. Read more about the moon and planets. There’s also a very faint comet in that part of the sky. Read more about the comet.

Two of the five bright planets rise to great prominence in January 2017 sky. Venus rules over the evening sky whereas Jupiter lords over the morning sky. Venus, the brightest planet, blazes in the west first thing at dusk, and reaches its greatest elongation as the “evening star” on January 12. Jupiter, the second-brightest planet, lords over the eastern half of sky between midnight and sunrise. Mars joins Venus in the evening sky, though it’s higher up and much fainter than Venus, setting in the west shortly after Venus does. Venus and Mars remain close together on the sky’s dome throughout January, whereas Saturn appears in the southeastern predawn/dawn sky. Seek for Mercury a short hop beneath Saturn, just as darkness is giving way to morning twilight. Follow the links below to learn more about planets in January 2017.

Brilliant Venus is the “evening star”

Mars, east of Venus, until mid-evening

Saturn returns to the morning sky

Bright Jupiter lords over morning sky

Mercury in the morning sky

Like what EarthSky offers? Sign up for our free daily newsletter today!

Astronomy events, star parties, festivals, workshops

Visit a new EarthSky feature – Best Places to Stargaze – and add your fav.

Skywatcher, by Predrag Agatonovic.

Watch for the waxing crescent moon to go by the planets Venus and Mars in early January 2017. Read more.

Brilliant Venus is the “evening star.” Okay, it’s not a star. It’s a planet. But people will call it the evening star all the same. In these past weeks, many have noticed Venus and been amazed at its brilliance in the west after sunset. It’s the brightest planet and very, very bright, to reach its greatest evening elongation on January 12.

Be sure to catch the waxing crescent moon near Venus in early January, as displayed on the sky chart above. Click here for details.

Watch for Venus to close the gap between itself and Mars. These two visible evening planets will be closer together on the sky’s dome by the month’s end and closer yet in early February 2017.

From mid-northern latitudes (U.S. and Europe), Venus sets about four hours after the sun throughout the month.

At mid-southern latitudes (Australia and South Africa), Venus sets about about three hours after the sun in early January and about 2.5 hours after sun by the month’s end.

Mars, east of Venus, until mid-evening. After appearing as a bright red light in our sky last May and June 2016, Mars now appears only modestly bright (though possibly still ruddy), above dazzling Venus. Venus is so bright that it pops out almost immediately after sunset, but you’ll have to wait until nightfall to see fainter Mars. Look for the moon close to Mars for a few evenings, on or near January 2 or 3.

From mid-northern latitudes (U.S. and Europe), look for the red planet Mars to set in the west around 9 to 10 p.m. all month long.

At mid-southern latitudes (Australia and South Africa), Mars sets in the west around 9 to 10 p.m. (10 to 11 p.m. summer time).

Mars will linger in our sky for several more months. Keep in mind, however, that Earth is traveling away from Mars as we speak – moving far ahead of this planet in the endless race around the sun – so Mars is dimming in our evening sky. Mars is in its long, lingering, relatively inconspicuous phase now. It’ll be still visible in the west to the unaided eye – though not prominent – during its conjunction with Uranus on the evening of February 27, 2017.

Mars won’t make its transition from the evening to morning sky until July 27, 2017. Even so, Mars’ stature in the evening sky will continue to diminish to that of a rather faint “star,” and we expect few – if any – skywatchers to observe the conjunction of Mars and Mercury in the evening sky on June 28, 2017.

The conjunction of Mars and Venus in the morning sky on October 5, 2017, may well present the first good opportunity to spot Mars in the morning sky when it returns from being behind the sun on July 27, 2017.

Looking for a sky almanac? EarthSky recommends…

View larger | Mikhail Chubarets in the Ukraine made this chart. It shows the view of Mars through a telescope in 2016. We never see Mars as a disk like this with the eye alone. But you can see why Mars was bright to the eye in 2016, and is now fading.

Watch for the moon to meet up with Saturn on or near Janaury 24, 2017. Read more.

Saturn returns to the morning sky. Saturn swung behind the sun on December 10, 2016, transitioning from the evening to morning sky.

In both the Northern and Southern Hemispheres, Saturn returned to the morning sky in late December 2016. In early January, Saturn rises in the east about two hours before the sun, and by the month’s end, Saturn comes up several hours before sunrise. Be sure to let the waning crescent moon guide you to Saturn (and the nearby star Antares) for several days, centered on or near January 24.

Saturn, the farthest world that you can easily view with the eye alone, appears golden in color. It shines with a steady light.

Binoculars don’t reveal Saturn’s gorgeous rings, by the way, although binoculars will enhance Saturn’s golden color. To see the rings, you need a small telescope. A telescope will also reveal one or more of Saturn’s many moons, most notably Titan.

Saturn’s rings are inclined at nearly 27^o from edge-on, exhibiting their northern face. In October 2017, the rings will open most widely, displaying a maximum inclination of 27^o.

As with so much in space (and on Earth), the appearance of Saturn’s rings from Earth is cyclical. In the year 2025, the rings will appear edge-on as seen from Earth. After that, we’ll begin to see the south side of Saturn’s rings, to increase to a maximum inclination of 27^o by May 2032.

Click here for recommended almanacs. They can help you know when the planets rise, transit and set in your sky

Tom Wildoner over-exposed Saturn itself to capture this view of Saturn’s moons on June 25, 2016. Visit Tom at LeisurelyScientist.com.

Contrasting the size of Saturn and its rings with our planet Earth via Hubble Heritage Team.

The moon swings by the planet Jupiter and the star Spica for several days, centered on or near January 19, 2017. .

Bright Jupiter lords over the morning sky. Jupiter’s increasing prominence as the “morning star” will be hard to overlook. To see Jupiter, seek out the brightest starlike object in the predawn sky or the morning twilight and that’ll be the king planet Jupiter! Jupiter rises in the east at late night and soars to its highest point in the sky at or near dawn.

From mid-northern latitudes, like those in the U.S. and Europe, Jupiter rises around one hour after the midnight hour in early January. By the month’s end, Jupiter rises roughly one hour before midnight.

From mid-southern latitudes (Australia), look for Jupiter to rise around midnight in early January and about two hours before midnight by the end of the month.

If you’re not a night owl, your best bet for catching Jupiter is to wake up before sunrise to see this brilliant beauty of a planet lighting up the predawn and dawn sky. Watch for the waning moon to join up with Jupiter for several days, centered on or near January 19. See the above sky chart.

By the way, Jupiter shines in front of the constellation Virgo, near Virgo’s brightest star, Spica. Jupiter serves a great reference for learning the constellations of the zodiac, because Jupiter stays in each constellation for roughly a year. So use Jupiter to become familiar with the star Spica and the constellation Virgo, starting now, and throughout 2017.

If you have binoculars or a telescope, it’s fairly easy to see Jupiter’s four major moons, which look like pinpricks of light on or near the same plane. They are often called the Galilean moons to honor Galileo, who discovered these great Jovian moons in 1610. In their order from Jupiter, these moons are Io, Europa, Ganymede and Callisto.

Jupiter and its four major moons via Jan Sandberg

These moons circle Jupiter around the Jovian equator. In cycles of six years, we view Jupiter’s equator edge-on. So, in 2015, we got to view a number of mutual events involving Jupiter’s moons through a high-powered telescope. Click here or here or here for more details.

Although Jupiter’s axial tilt is only 3^o out of perpendicular relative to the ecliptic (Earth’s orbital plane), Jupiter’s axis will tilt enough toward the sun and Earth so that the farthest of these four moons, Callisto, will NOT pass in front of Jupiter or behind Jupiter for a period of about three years, starting in late 2016. During this approximate 3-year period, Callisto will remain “perpetually” visible, alternately swinging “above” and “below” Jupiter.

Click here for a Jupiter’s moons almanac, courtesy of Sky & Telescope.

Eliot Herman in Tucson, Arizona caught Mercury on the night of December 11, 2016, amidst crepuscular rays from the setting sun.

Look for the thin waning crescent moon and the planet Mercury low in the sky as the predawn darkness gives way to dawn. Who knows? Someone might even catch the moon below Mercury on January 26! The green line depicts the ecliptic – Earth’s orbital plane projected on the sky. Read more.

Mercury in the morning sky. Mercury transitioned from the evening to morning sky on December 28, 2016. This month, beginning in the second week of January 2017, Mercury should climb far enough from the glare of sunrise to become visible in the morning sky from both the Northern Hemisphere and the Southern Hemisphere. Saturn rises before Mercury does, so use Saturn as your guide “star” to locating Mercury closer to the horizon.

Try viewing Mercury before sunrise for a few weeks, centered on Mercury’s greatest morning elongation on January 19. Mercury is tricky. If you look too soon, Mercury will be lost in the twilight glare; if you look too late, it will have followed the sun beneath the horizon. Watch for Mercury low in the sky, and near the sunrise point on the horizon, seeking for this hidden treasure around 90 to 60 minutes before sunrise. Remember, binoculars are always helpful for any Mercury search. Good Luck!

For a big challenge, seek for the slender waning crescent moon pairing up with Mercury before sunrise on January 25 and 26. Binoculars may come in handy!

Click here for recommended almanacs; they can give you Mercury’s rising time in your sky.

What do we mean by bright planet? By bright planet, we mean any solar system planet that is easily visible without an optical aid and that has been watched by our ancestors since time immemorial. In their outward order from the sun, the five bright planets are Mercury, Venus, Mars, Jupiter and Saturn. These planets actually do appear bright in our sky. They are typically as bright as – or brighter than – the brightest stars. Plus, these relatively nearby worlds tend to shine with a steadier light than the distant, twinkling stars. You can spot them, and come to know them as faithful friends, if you try.

From late January, and through mid-February, 5 bright planets were visible at once in the predawn sky. This image is from February 8, 2016. It’s by Eliot Herman in Tucson, Arizona. View on Flickr.

Bottom line: In January 2017, two of the five bright planets appear in the evening sky at dusk/nightfall: Venus and Mars. The other three planets – Jupiter, Saturn and Mercury – are found in the morning sky.

Easily locate stars and constellations with EarthSky’s planisphere.

Don’t miss anything. Subscribe to EarthSky News by email

from EarthSky http://ift.tt/IJfHCr

Northerly latitude? Try the Quadrantids

View larger. | In 2014, as the Quadrantids were flying, those at far northern latitudes were seeing auroras. Photo by Tommy Eliassen.

The Quadrantid meteor shower is 2017’s first major meteor shower. The good news is that, in 2017, a fat waxing crescent moon won’t interfere with the shower. Now the not-so-good news. Although the Quadrantids have been known to produce some 50-100 meteors in a dark sky, their peak is extremely narrow. Peaks of the Perseid or Geminid meteor showers persist for a day or more, allowing all time zones around the world to enjoy a good display of Perseids and Geminids. But the Quadrantids’ peak lasts only a few hours. So you have to be on the right part of Earth – preferably with the radiant high in your sky – in order to experience the peak of the Quadrantids. What’s more, the shower favors the Northern Hemisphere because its radiant point is so far north on the sky’s dome. Follow the links below to learn more about the Quadrantids in 2017.

Peak dates for the Quadrantid shower in 2017

Where is the Quadrantids’ radiant point?

The Quadrantids are named for a constellation that no longer exists.

Quadrantid meteors have a mysterious parent object.

Barry Simmons in Lake Martin, Alabama captured this Quadrantid meteor on the morning of January 3, 2014. Thank you, Barry.

Peak dates for the Quadrantid shower in 2017 Different sources give different dates and precise times for meteor shower peaks. In 2017, various sources – such as the International Meteor Organization and the Society for Popular Astronomy in the U.K. – give the peak as January 3 at 14:00 UTC.

If that prediction holds true, the Americas will have the best shot at the shower on the morning of January 3. Those in Asia should try the hours after midnight on the morning of January 4.

But predictions aren’t always accurate, so from any northerly latitudes, try watching in the dark hours before dawn on January 3 and/or 4.

So you see … this shower is a gamble!

From mid-northern latitudes, the radiant point for the Quadrantid shower doesn’t climb over the horizon until after midnight.

Where is the Quadrantids’ radiant point? All other things being equal, for any meteor shower, you are likely to see the most meteors when the radiant is high in the sky. In the case of the Quadrantid shower, the radiant point is seen highest in the sky in the dark hour before dawn.

The radiant point of the Quadrantid shower makes an approximate right angle with the Big Dipper and the bright star Arcturus. If you trace the paths of the Quadrantid meteors backward, they appear to radiate from this point on the starry sky.

Now for our usual caveat. You don’t need to find the meteor shower radiant to see the Quadrantid meteors.

You just have to be at mid-northern or far-northern latitudes, up in the wee hours of the morning and hope the peak comes at just the right time to your part of the world. The meteors will radiate from the northern sky, but appear in all parts of the sky.

The now-defunct constellation Quadrans Muralis, for which the Quadrantids are named. Image via Atlas Coelestis.

The Quadrantids are named for a constellation that no longer exists. Most meteor showers are named for the constellations from which they appear to radiate. So it is with the Quadrantids. But the Quadrantids’ constellation no longer exists, except in memory. The name Quadrantids comes from the constellation Quadrans Muralis (Mural Quadrant), created by the French astronomer Jerome Lalande in 1795. This now-obsolete constellation was located between the constellations of Bootes the Herdsman and Draco the Dragon. Where did it go?

To understand the history of the Quadrantids’ name, we have to go back to the earliest observations of this shower. In early January 1825, Antonio Brucalassi in Italy reported that:

… the atmosphere was traversed by a multitude of the luminous bodies known by the name of falling stars.

They appeared to radiate from Quadrans Muralis. In 1839, Adolphe Quetelet of Brussels Observatory in Belgium and Edward C. Herrick in Connecticut independently made the suggestion that the Quadrantids are an annual shower.

But, in 1922, the International Astronomical Union devised a list 88 modern constellations. The list was agreed upon by the International Astronomical Union at its inaugural General Assembly held in Rome in May 1922. It did not include a constellation Quadrans Muralis.

Today, this meteor shower retains the name Quadrantids, for the original and now obsolete constellation Quadrans Muralis.

The radiant point for the Quadrantids is now considered to be at the northern tip of Bootes, near the Big Dipper asterism in our sky, not far from Bootes’ brightest star Arcturus. It is very far north on the sky’s dome, which is why Southern Hemisphere observers probably won’t see many (if any) Quadrantid meteors. Most of the meteors simply won’t make it above the horizon for Southern Hemisphere skywatchers. But some might!

In 2003, Peter Jenniskens proposed that this object, 2003 EH1, is the parent body of the Quadrantid meteor shower.

Quadrantid meteors have a mysterious parent object. In 2003, astronomer Peter Jenniskens tentatively identified the parent body of the Quadrantids as the asteroid 2003 EH1. If indeed this body is the Quadrantids parent, then the Quadrantids, like the Geminid meteors, come from a rocky body – not an icy comet. Strange.

In turn, though, 2003 EH1 might be the same object as the comet C/1490 Y1, which was observed by Chinese, Japanese and Korean astronomers 500 years ago.

So the exact story behind the Quadrantids’ parent object remains somewhat mysterious.

Bottom line: The first major meteor shower of 2017, and every year, the Quadrantid meteor shower, will probably be at its best in the hours between midnight and dawn January 3 or 4. This shower is best for the Northern Hemisphere because its radiant point is far to the north on the sky’s dome.

Celebrate 2017 with an EarthSky moon calendar!

from EarthSky http://ift.tt/1lsGXYp

View larger. | In 2014, as the Quadrantids were flying, those at far northern latitudes were seeing auroras. Photo by Tommy Eliassen.

The Quadrantid meteor shower is 2017’s first major meteor shower. The good news is that, in 2017, a fat waxing crescent moon won’t interfere with the shower. Now the not-so-good news. Although the Quadrantids have been known to produce some 50-100 meteors in a dark sky, their peak is extremely narrow. Peaks of the Perseid or Geminid meteor showers persist for a day or more, allowing all time zones around the world to enjoy a good display of Perseids and Geminids. But the Quadrantids’ peak lasts only a few hours. So you have to be on the right part of Earth – preferably with the radiant high in your sky – in order to experience the peak of the Quadrantids. What’s more, the shower favors the Northern Hemisphere because its radiant point is so far north on the sky’s dome. Follow the links below to learn more about the Quadrantids in 2017.

Peak dates for the Quadrantid shower in 2017

Where is the Quadrantids’ radiant point?

The Quadrantids are named for a constellation that no longer exists.

Quadrantid meteors have a mysterious parent object.

Barry Simmons in Lake Martin, Alabama captured this Quadrantid meteor on the morning of January 3, 2014. Thank you, Barry.

Peak dates for the Quadrantid shower in 2017 Different sources give different dates and precise times for meteor shower peaks. In 2017, various sources – such as the International Meteor Organization and the Society for Popular Astronomy in the U.K. – give the peak as January 3 at 14:00 UTC.

If that prediction holds true, the Americas will have the best shot at the shower on the morning of January 3. Those in Asia should try the hours after midnight on the morning of January 4.

But predictions aren’t always accurate, so from any northerly latitudes, try watching in the dark hours before dawn on January 3 and/or 4.

So you see … this shower is a gamble!

From mid-northern latitudes, the radiant point for the Quadrantid shower doesn’t climb over the horizon until after midnight.

Where is the Quadrantids’ radiant point? All other things being equal, for any meteor shower, you are likely to see the most meteors when the radiant is high in the sky. In the case of the Quadrantid shower, the radiant point is seen highest in the sky in the dark hour before dawn.

The radiant point of the Quadrantid shower makes an approximate right angle with the Big Dipper and the bright star Arcturus. If you trace the paths of the Quadrantid meteors backward, they appear to radiate from this point on the starry sky.

Now for our usual caveat. You don’t need to find the meteor shower radiant to see the Quadrantid meteors.

You just have to be at mid-northern or far-northern latitudes, up in the wee hours of the morning and hope the peak comes at just the right time to your part of the world. The meteors will radiate from the northern sky, but appear in all parts of the sky.

The now-defunct constellation Quadrans Muralis, for which the Quadrantids are named. Image via Atlas Coelestis.

The Quadrantids are named for a constellation that no longer exists. Most meteor showers are named for the constellations from which they appear to radiate. So it is with the Quadrantids. But the Quadrantids’ constellation no longer exists, except in memory. The name Quadrantids comes from the constellation Quadrans Muralis (Mural Quadrant), created by the French astronomer Jerome Lalande in 1795. This now-obsolete constellation was located between the constellations of Bootes the Herdsman and Draco the Dragon. Where did it go?

To understand the history of the Quadrantids’ name, we have to go back to the earliest observations of this shower. In early January 1825, Antonio Brucalassi in Italy reported that:

… the atmosphere was traversed by a multitude of the luminous bodies known by the name of falling stars.

They appeared to radiate from Quadrans Muralis. In 1839, Adolphe Quetelet of Brussels Observatory in Belgium and Edward C. Herrick in Connecticut independently made the suggestion that the Quadrantids are an annual shower.

But, in 1922, the International Astronomical Union devised a list 88 modern constellations. The list was agreed upon by the International Astronomical Union at its inaugural General Assembly held in Rome in May 1922. It did not include a constellation Quadrans Muralis.

Today, this meteor shower retains the name Quadrantids, for the original and now obsolete constellation Quadrans Muralis.

The radiant point for the Quadrantids is now considered to be at the northern tip of Bootes, near the Big Dipper asterism in our sky, not far from Bootes’ brightest star Arcturus. It is very far north on the sky’s dome, which is why Southern Hemisphere observers probably won’t see many (if any) Quadrantid meteors. Most of the meteors simply won’t make it above the horizon for Southern Hemisphere skywatchers. But some might!

In 2003, Peter Jenniskens proposed that this object, 2003 EH1, is the parent body of the Quadrantid meteor shower.

Quadrantid meteors have a mysterious parent object. In 2003, astronomer Peter Jenniskens tentatively identified the parent body of the Quadrantids as the asteroid 2003 EH1. If indeed this body is the Quadrantids parent, then the Quadrantids, like the Geminid meteors, come from a rocky body – not an icy comet. Strange.

In turn, though, 2003 EH1 might be the same object as the comet C/1490 Y1, which was observed by Chinese, Japanese and Korean astronomers 500 years ago.

So the exact story behind the Quadrantids’ parent object remains somewhat mysterious.

Bottom line: The first major meteor shower of 2017, and every year, the Quadrantid meteor shower, will probably be at its best in the hours between midnight and dawn January 3 or 4. This shower is best for the Northern Hemisphere because its radiant point is far to the north on the sky’s dome.

Celebrate 2017 with an EarthSky moon calendar!

from EarthSky http://ift.tt/1lsGXYp

2016 SkS Weekly Climate Change & Global Warming Digest #53

Story of the Week... SkS Highlights... La Niña Update... Toon of the Week... Quote of the Week... Graphic of the Week... SkS in the News... SkS Spotlights... Video of the Week... Coming Soon on SkS... Poster of the Week... Climate Feedback Reviews... SkS Week in Review... 97 Hours of Consensus...

Happy New Tropical Earth Orbital Period! Kinda!

Yay! It’s a new year!

But what does that mean, exactly?

The year, of course, is the time it takes for the Earth to go around the Sun, right? Well, not exactly. It depends on what you mean by “year” and how you measure it. This takes a wee bit of explaining, so if you're done kicking 2016 to the curb and trying your best to hope for 2017, sit back and let me tell you why we have a new year at all.

Happy New Tropical Earth Orbital Period! Kinda! by Phil Plait, Bad Astronomy, Slate, Jan 1, 2017

Story of the Week...

Heat Is On for 2017, Just Not Record-Setting

2016 is about to cap off the hottest year on record for the third straight year, a remarkable streak fueled primarily by the excess heat trapped in Earth’s atmosphere by ever-rising levels of greenhouse gases.

While that streak is expected to end, in part because of the demise of one of the strongest El Niños on record, 2017 is still expected to be among the hottest years in more than 130 years of record keeping, according to a forecast from the U.K. Met Office.

The U.K. Met Office's forecast for 2017's global annual average temperature. Credit: Met Office

Because of global warming, “each new year is basically predestined to be among the warmest on record,” Deke Arndt, chief of the monitoring branch of the U.S. National Centers for Environmental Information, said in an email.

Because of global warming, 16 of the 17 hottest years on record have occurred this century, the only exception being the strong El Niño year of 1998.

Each year, the Met Office uses climate models to forecast the global annual average temperature for the coming decade, in an effort to improve shorter-term climate forecasting of features like hurricane season activity and droughts.

Forecasters expect 2017’s temperature to fall between 1.13°F (0.63 °C) and 1.57°F (0.87 °C) above the 1961-1990 average.

Heat Is On for 2017, Just Not Record-Setting by Andrea Thompson, Climate Central, Dec 30, 2016

SkS Highlights...

[To be added] 

Toon of the Week...

 

Hat tip to I Heart Climate Scientists.

Quote of the Week...

[To be added]  

Graphic of the Week...

[To be added]  

SkS in the News...

[To be added]  

SkS Spotlights...

[To be added]  

Video of the Week...

[To be added]  

Coming Soon on SkS...

• Climate change in 2016: the good, the bad, and the ugly (John Abraham)
• As Seas Rise, Miami Development Continues Unabated (Peter Sinclair)
• Prepare for reanimation of the zombie myth ‘no global warming since 2016’ (Dana)
• What could the rest of the world do if Trump pulls the US out of the Paris Agreement on climate change? (Henrik Selen, Adil Najam)
• Zika outbreak ‘fuelled by’ El Niño and climate change (Robert McSweeney)
• 2017 SkS Weekly Climate Change & Global Warming News Roundup #1 (John Hartz)
• 2017 SkS Weekly Climate Change & Global Waming Digest #1 (John Hartz)

Poster of the Week...

 

Hat tip to I Heart Climate Scientists.

Climate Feedback Reviews...

[To be added]  

SkS Week in Review...

[To be added] 

97 Hours of Consensus...

 

 

Timothy Naish's bio page

Quote derived with from:

"If you maintain carbon dioxide levels of 400ppm and commit the planet to an atmosphere of that composition for the next 100 years, then you stand a chance of losing both the Greenland Ice Sheet and the West Antarctic Ice Sheet, having sea level potentially 10m (higher) than it is today." 

High resolution JPEG (1024 pixels wide)

from Skeptical Science http://ift.tt/2iTQFYe

Story of the Week... SkS Highlights... La Niña Update... Toon of the Week... Quote of the Week... Graphic of the Week... SkS in the News... SkS Spotlights... Video of the Week... Coming Soon on SkS... Poster of the Week... Climate Feedback Reviews... SkS Week in Review... 97 Hours of Consensus...

Happy New Tropical Earth Orbital Period! Kinda!

Yay! It’s a new year!

But what does that mean, exactly?

The year, of course, is the time it takes for the Earth to go around the Sun, right? Well, not exactly. It depends on what you mean by “year” and how you measure it. This takes a wee bit of explaining, so if you're done kicking 2016 to the curb and trying your best to hope for 2017, sit back and let me tell you why we have a new year at all.

Happy New Tropical Earth Orbital Period! Kinda! by Phil Plait, Bad Astronomy, Slate, Jan 1, 2017

Story of the Week...

Heat Is On for 2017, Just Not Record-Setting

2016 is about to cap off the hottest year on record for the third straight year, a remarkable streak fueled primarily by the excess heat trapped in Earth’s atmosphere by ever-rising levels of greenhouse gases.

While that streak is expected to end, in part because of the demise of one of the strongest El Niños on record, 2017 is still expected to be among the hottest years in more than 130 years of record keeping, according to a forecast from the U.K. Met Office.

The U.K. Met Office's forecast for 2017's global annual average temperature. Credit: Met Office

Because of global warming, “each new year is basically predestined to be among the warmest on record,” Deke Arndt, chief of the monitoring branch of the U.S. National Centers for Environmental Information, said in an email.

Because of global warming, 16 of the 17 hottest years on record have occurred this century, the only exception being the strong El Niño year of 1998.

Each year, the Met Office uses climate models to forecast the global annual average temperature for the coming decade, in an effort to improve shorter-term climate forecasting of features like hurricane season activity and droughts.

Forecasters expect 2017’s temperature to fall between 1.13°F (0.63 °C) and 1.57°F (0.87 °C) above the 1961-1990 average.

Heat Is On for 2017, Just Not Record-Setting by Andrea Thompson, Climate Central, Dec 30, 2016

SkS Highlights...

[To be added] 

Toon of the Week...

 

Hat tip to I Heart Climate Scientists.

Quote of the Week...

[To be added]  

Graphic of the Week...

[To be added]  

SkS in the News...

[To be added]  

SkS Spotlights...

[To be added]  

Video of the Week...

[To be added]  

Coming Soon on SkS...

• Climate change in 2016: the good, the bad, and the ugly (John Abraham)
• As Seas Rise, Miami Development Continues Unabated (Peter Sinclair)
• Prepare for reanimation of the zombie myth ‘no global warming since 2016’ (Dana)
• What could the rest of the world do if Trump pulls the US out of the Paris Agreement on climate change? (Henrik Selen, Adil Najam)
• Zika outbreak ‘fuelled by’ El Niño and climate change (Robert McSweeney)
• 2017 SkS Weekly Climate Change & Global Warming News Roundup #1 (John Hartz)
• 2017 SkS Weekly Climate Change & Global Waming Digest #1 (John Hartz)

Poster of the Week...

 

Hat tip to I Heart Climate Scientists.

Climate Feedback Reviews...

[To be added]  

SkS Week in Review...

[To be added] 

97 Hours of Consensus...

 

 

Timothy Naish's bio page

Quote derived with from:

"If you maintain carbon dioxide levels of 400ppm and commit the planet to an atmosphere of that composition for the next 100 years, then you stand a chance of losing both the Greenland Ice Sheet and the West Antarctic Ice Sheet, having sea level potentially 10m (higher) than it is today." 

High resolution JPEG (1024 pixels wide)

from Skeptical Science http://ift.tt/2iTQFYe

Comments of the Week #142: from the speed of light to fundamental constants [Starts With A Bang]

“Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.” -Winston Churchill

Happy new year here at Starts With A Bang! No matter how 2016 was for you, there’s a new year dawning today, and whether you’ve got sun, clouds, rain or snow where you are (it’s snow here), the Universe beyond our world is still a tremendous place to explore. The latest Starts With A Bang podcast, on whether our Universe itself could be the inside of a black hole, turned into such a sensation (with more listens than any other podcast we’ve done) that I’ve decided to re-post it here:

While this coming week will see the start of some incredible stories from the American Astronomical Society’s annual meeting (schedule here if you have recommendations for what you want to see an article on), there’s always time to look back on the last articles of 2016:

• Could we reach the speed of light by Christmas? (for Ask Ethan),
• Hubble’s shining view of deep space beyond the stars (for Mostly Mute Monday),
• Gravitational waves: from discovery of the year to science of the century,
• Finding darkness in the light: how Vera Rubin changed the Universe,
• The four biggest mistakes of Einstein’s scientific life, and
• How many fundamental constants does it take to define our Universe?

While last year may be gone, the best of your thoughts, ideas and comments are here to help us ring in the new year. Let’s get into the start of 2017 with your comments of the week!

The dimming of Tabby’s star, KIC 8462852. Image credit: Bradley E. Schaefer, via http://ift.tt/1N8vngL.

From Sinisa Lazarek on long-term dimming of Tabby’s star: “The overall century dimming I got from this paper which is linked on wiki. http://ift.tt/2hZSraB
Am not skilled to judge anyone’s findings on this matter. But agree with you that when looking at the magnitude measurements you posted, it’s far less apparent or true.”

Well, the table above is from the very paper you linked to; it’s very difficult to do long-term studies because of differences in equipment. Looking at Tabby’s star, its brightness varies by about 0.2 magnitudes, mostly decreasing over time. But the two reference stars vary by 0.11 and 0.12 magnitudes, respectively, with increases and decreases also. But that also underscores why the Kepler data is so interesting; as Sinisa discovered later (quote from this paper):

Over the first ~1000 days, KIC 8462852 faded approximately linearly at a rate of 0.341 +/- 0.041%/yr, for a total decline of 0.9%. KIC 8462852 then dimmed much more rapidly in the next ~200 days, with its flux dropping by more than 2%. For the final ~200 days of Kepler photometry the magnitude remained approximately constant…

So why is the flux dropping? And why does it drop in weird, strange patterns? And why is it so different from all the other stars we know of? This is one of the most fun mysteries in science, and no matter how it turns out, we’re going to learn something incredible about the Universe.

Different ways of measuring cosmological distances in the expanding Universe. Image credit: Wesino at English Wikipedia.

From Omega Centauri on distances in the Universe: “From one standpoint, that of determining the inverse square law dimming of the light, only one of these “distances” will give the correct result (there is also a factor due to the decrease in frequency, but that is a separate multiplicative factor), there should be only one correct distance. I think this distance is the same as that which determines the reduction in the solid angle of the sky the object occupies.”

You have to be very careful to get those multiplicative factors correct, especially when you go to large distances. We have this (incorrect) intuitive notion that as you look farther and farther away, objects will appear fainter (as 1/distance^2) and smaller (as 1/distance) on the sky… but that’s only partly true. Once you reach a redshift of about 0.1, there are corrective, redshift-dependent terms. There’s actually a minimum angular size objects will reach, so beyond a certain redshift, stars and galaxies will appear larger again! If we had a 10 meter-class telescope in space, we could resolve the internal structure of pretty much any galaxy in the Universe. That’s pretty incredible!

An older view (pre-main injector) of Fermilab, as I remember it best from 1997. Image credit: Fermi National Accelerator Laboratory, a.k.a. Fermilab.

From Michael Kelsey on my introduction to physics research: “what experiment did you work on?”

There comes a time in every aspiring scientist’s life where they get exposed to research for the first time, and it rarely looks like you’d expect. In the summer of 1997, I started working for a professor who was testing various detectors for the D0 experiment on the fixed-target beamline. I got to tune the electromagnets focusing the beam, perform voltage tests on the detectors, study angular variations in the detectors’ sensitivities and other duties like that. It was honestly an incredible experience for learning about myself, what I was interested in, and what I was/wasn’t passionate about more than anything else.

My best memories of that summer were of the time I spent with Roger Dixon and Erik Ramberg, who led groups of undergrads (maybe 10-12 of us) on some incredible journeys through particle physics. I also remember Drasko Jovanovich, whose Fermilab badge ID# was 7. (Mine was 8000-something.) Experimental particle physics turned out to be something I was “good enough” at but not great at, but getting exposed to it at all, as I did, was an incredible and formative experience for me.

A multistage rocket that lost and jettisoned mass as it moved faster and faster would be required to reach speeds approaching the speed of light, like the Super Haas rocket shown here. Image credit: Dragos muresan, under c.c.a.-s.a.-3.0.

From G on acceleration via spaceship/propulsion: “What’s a reasonable consensus estimate of the highest velocity that could be reached using hydrogen fusion as the means of propulsion?”

As Michael Kelsey said, there is no upper limit, but there is a terrible tradeoff: the longer you want to accelerate for, the more fuel you need to bring. If your fuel is not energy efficient (chemical is worse than nuclear is worse than antimatter), this gets you in trouble quickly. Why? You need to not only accelerate your payload, but all the remaining fuel you have on board. This is why rockets jettison their used-up stages, so you don’t have to keep accelerating all that mass. There’s no technical limit for the speed you can reach (or the amount of time you can accelerate for), but depending on your fuel’s efficiency — and hydrogen fusion is about 0.7% efficient — you’re going to be limited by the mass/size of your initial rocket, fuel included.

Light and ripples in space; as the light passes through non-flat space, it changes how an observer at any other location perceives the passage of time for the light. Image credit: European Gravitational Observatory, Lionel BRET/EUROLIOS.

From ketchup on how we talk about time in the expanding Universe: “You mean the merger was detected on September 14th, 2015. Since it happened over a billion light years away, and gravitational waves travel at the speed of light, the merger itself was hundreds of millions of years ago.”

We have a lot of conventions in astronomy, and many of them make people unhappy. Which is unsurprising, since a convention in how we refer to things is a choice, and not everyone has the same personal preferences. Since there are no such things as absolute space or time, however, we talk about the arrival of the first signal of the “event” as when the event occurred.

Two merging black holes, particularly in the final stages of merger, emit tremendous amounts of gravitational waves. Image Credit: SXS, the Simulating eXtreme Spacetimes (SXS) project (http://ift.tt/10eTU31).

For these black holes that created LIGO’s first event, the merger did occur some billion+ years ago; the gravitational waves traveled through space for all that time; they arrived on Earth about 16 months ago; we detected them as soon as they arrived. But when we talk about when the event occurred, we’ll conventionally say it occurred the moment it was detected. Measurements of the CMB are occurring right now, and we can talk about the CMB “today,” even though the light is from 13.8 billion years ago. It’s not right or wrong to make a different choice, but this is how people talk about this.

How single stars end their lives, depending on initial mass. Image credit: A. Heger et al., 2003, via http://ift.tt/2iVS9FH

From Wow on IMBHs (intermediate mass black holes): “A black hole loses MOST of its mass in ejection during the supernova. A 60 solar mass star may form a 6 solar mass black hole. […] Therefore to get to mid size, a black hole has to accrete the extra matter.”

Kind of. If you form a massive enough star (or a metal-free-enough star that’s modestly heavy), you can get a direct black hole, where 100% of the star’s mass becomes a black hole. Intermediate mass black holes, however, are outstanding candidates for dynamically relaxing and heading towards the galactic center, where they contribute to the merger and growth of the central, supermassive behemoths present. If you want to look for them, the best place is within the central few hundred parsecs of a galactic center, and we expect to find many between, say, 20 and a few hundred thousand solar masses. The large black holes found by LIGO’s first detected merger — 36 + 29 becomes 62 solar masses — were the first black holes robustly found in this mass range.

A clumpy dark matter halo with varying densities and a very large, diffuse structure, as predicted by simulations, with the luminous part of the galaxy shown for scale. Image credit: NASA, ESA, and T. Brown and J. Tumlinson (STScI).

From Omega Centauri on dark matter and star wars: “I realized a couple of weeks back, watching “A New Hope”, that the Jedi knew of dark matter a long time ago. ObiOne (sic) describing the force “it binds the galaxies together…””

Dark matter does surround us, it does penetrate us, and it does bind the galaxy together. But unless we can figure out how to coax it into interacting with either itself or some form of matter in a way that goes beyond standard gravitation, we’re never going to directly detect it. Or, you know, use it to move material objects or choke an incompetent Captain.

Albert Einstein in 1920. Image credit: “The Solar Eclipse of May 29, 1919, and the Einstein Effect,” The Scientific Monthly 10:4 (1920), 418-422, on p. 418. Public domain.

From Amos Dettenville on Einstein’s blunders: “I think the first item on your list is wrong. You do a dis-service to your readers by contributing to the spread of the erroneous claims of Ives (anti-relativity crank) and Ohanian, et al. Genuine scholars like Stachel and Torretti long ago debunked the mistaken ideas that you’ve repeated in your Forbes article. For a good recent overview of the facts, see http://ift.tt/2iVZ1mA.”

There is a colorful history of this controversy, that involves anti-semitism, relativity denialism, but also some genuine flaws and incomplete analysis/understanding in the early days. As is usually, the case, I was aware of some of it (Ives, Hasenöhrl) but not all of it (the Field paper). What I said in the article, that I believe still holds up, is:

Einstein was only able to derive E = mc^2 for a particle completely at rest. Despite also inventing special relativity — founded on the principle that the laws of physics are independent of an observer’s frame of reference — Einstein’s formulation couldn’t account for how energy worked for a particle in motion. In other words, E = mc^2 as derived by Einstein was frame-dependent!

The big advance of von Laue, which I think deserves a ton of credit, is that in 1911, he was the first to realize that inertial mass doesn’t mean what it does in classical (Newtonian) mechanics. Around 1911, von Laue made a formulation of a flow of continuous matter in special relativity. “Mass” doesn’t fully characterize the inertial behavior of an extended physical system, and that’s the incompleteness of Einstein’s E = mc^2. Max von Laue made it clear that you need, at minimum, 10 functions, which would become the 10 independent components of the stress-energy tensor in General Relativity. The story I’m most familiar with comes from this book, which is an incredibly informative look at the original source material.

The particles and forces of the Standard Model. Image credit: Contemporary Physics Education Project / DOE / NSF / LBNL, via http://cpepweb.org/.

From Lloyd Hargrove on questionable quotables: “Aleister Crowley? Really?”

Even people who we otherwise dislike, for whatever reasons, may make some amazing statements of wisdom. I have quoted Oprah, Aquinas, Ken Ham and Crowley, among others, and won’t stop quoting someone who says something interesting or thought-provoking just because they say or believe other things that I think are insane. The Crowley quote, by the way, was:

The joy of life consists in the exercise of one’s energies, continual growth, constant change, the enjoyment of every new experience. To stop means simply to die. The eternal mistake of mankind is to set up an attainable ideal.

Large scale projection through the Illustris volume at z=0, centered on the most massive cluster, 15 Mpc/h deep. Shows dark matter density (left) transitioning to gas density (right). The large-scale structure of the Universe cannot be explained without dark matter. Image credit: Illustris Collaboration / Illustris Simulation, via http://ift.tt/1mDBler.

And finally, from Mark Thomas on our finely-tuned Universe: “If ‘initial conditions’ are very close it will not produce an exact outcome of our Universe but a similar 4 dimensional Standard Model Universe with near similar dimensionless constants. To obtain the very exact same ‘initial conditions’ which would produce an exact replica of our Universe might be very improbable. This might produce a vast array of similar Universes as the ‘initial condition’ spectrum may be very large.”

One of the interesting questions one can ask ourselves is how close the Universe needs to be to our own to give a similar Universe. If you vary some of the fundamental constants by a small amount, you’ll get a Universe that’s only slightly different from our own, and where intelligent life is possible. But other constants could vary by a little — or if you vary the wrong constant by just enough — and that will ruin everything! There is an incredible book that I’ve just started reading that addresses this very concept: A Fortunate Universe by Geraint Lewis and Luke Barnes. In fact, maybe I’ll finish it and do a review sometime soon.

In any case, hope your new year is off to a great start and hope that 2017 is full of happiness, wellness and fulfillment for all of you!

from ScienceBlogs http://ift.tt/2iVU5hm

“Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.” -Winston Churchill

Happy new year here at Starts With A Bang! No matter how 2016 was for you, there’s a new year dawning today, and whether you’ve got sun, clouds, rain or snow where you are (it’s snow here), the Universe beyond our world is still a tremendous place to explore. The latest Starts With A Bang podcast, on whether our Universe itself could be the inside of a black hole, turned into such a sensation (with more listens than any other podcast we’ve done) that I’ve decided to re-post it here:

While this coming week will see the start of some incredible stories from the American Astronomical Society’s annual meeting (schedule here if you have recommendations for what you want to see an article on), there’s always time to look back on the last articles of 2016:

• Could we reach the speed of light by Christmas? (for Ask Ethan),
• Hubble’s shining view of deep space beyond the stars (for Mostly Mute Monday),
• Gravitational waves: from discovery of the year to science of the century,
• Finding darkness in the light: how Vera Rubin changed the Universe,
• The four biggest mistakes of Einstein’s scientific life, and
• How many fundamental constants does it take to define our Universe?

While last year may be gone, the best of your thoughts, ideas and comments are here to help us ring in the new year. Let’s get into the start of 2017 with your comments of the week!

The dimming of Tabby’s star, KIC 8462852. Image credit: Bradley E. Schaefer, via http://ift.tt/1N8vngL.

From Sinisa Lazarek on long-term dimming of Tabby’s star: “The overall century dimming I got from this paper which is linked on wiki. http://ift.tt/2hZSraB
Am not skilled to judge anyone’s findings on this matter. But agree with you that when looking at the magnitude measurements you posted, it’s far less apparent or true.”

Well, the table above is from the very paper you linked to; it’s very difficult to do long-term studies because of differences in equipment. Looking at Tabby’s star, its brightness varies by about 0.2 magnitudes, mostly decreasing over time. But the two reference stars vary by 0.11 and 0.12 magnitudes, respectively, with increases and decreases also. But that also underscores why the Kepler data is so interesting; as Sinisa discovered later (quote from this paper):

Over the first ~1000 days, KIC 8462852 faded approximately linearly at a rate of 0.341 +/- 0.041%/yr, for a total decline of 0.9%. KIC 8462852 then dimmed much more rapidly in the next ~200 days, with its flux dropping by more than 2%. For the final ~200 days of Kepler photometry the magnitude remained approximately constant…

So why is the flux dropping? And why does it drop in weird, strange patterns? And why is it so different from all the other stars we know of? This is one of the most fun mysteries in science, and no matter how it turns out, we’re going to learn something incredible about the Universe.

Different ways of measuring cosmological distances in the expanding Universe. Image credit: Wesino at English Wikipedia.

From Omega Centauri on distances in the Universe: “From one standpoint, that of determining the inverse square law dimming of the light, only one of these “distances” will give the correct result (there is also a factor due to the decrease in frequency, but that is a separate multiplicative factor), there should be only one correct distance. I think this distance is the same as that which determines the reduction in the solid angle of the sky the object occupies.”

You have to be very careful to get those multiplicative factors correct, especially when you go to large distances. We have this (incorrect) intuitive notion that as you look farther and farther away, objects will appear fainter (as 1/distance^2) and smaller (as 1/distance) on the sky… but that’s only partly true. Once you reach a redshift of about 0.1, there are corrective, redshift-dependent terms. There’s actually a minimum angular size objects will reach, so beyond a certain redshift, stars and galaxies will appear larger again! If we had a 10 meter-class telescope in space, we could resolve the internal structure of pretty much any galaxy in the Universe. That’s pretty incredible!

An older view (pre-main injector) of Fermilab, as I remember it best from 1997. Image credit: Fermi National Accelerator Laboratory, a.k.a. Fermilab.

From Michael Kelsey on my introduction to physics research: “what experiment did you work on?”

There comes a time in every aspiring scientist’s life where they get exposed to research for the first time, and it rarely looks like you’d expect. In the summer of 1997, I started working for a professor who was testing various detectors for the D0 experiment on the fixed-target beamline. I got to tune the electromagnets focusing the beam, perform voltage tests on the detectors, study angular variations in the detectors’ sensitivities and other duties like that. It was honestly an incredible experience for learning about myself, what I was interested in, and what I was/wasn’t passionate about more than anything else.

My best memories of that summer were of the time I spent with Roger Dixon and Erik Ramberg, who led groups of undergrads (maybe 10-12 of us) on some incredible journeys through particle physics. I also remember Drasko Jovanovich, whose Fermilab badge ID# was 7. (Mine was 8000-something.) Experimental particle physics turned out to be something I was “good enough” at but not great at, but getting exposed to it at all, as I did, was an incredible and formative experience for me.

A multistage rocket that lost and jettisoned mass as it moved faster and faster would be required to reach speeds approaching the speed of light, like the Super Haas rocket shown here. Image credit: Dragos muresan, under c.c.a.-s.a.-3.0.

From G on acceleration via spaceship/propulsion: “What’s a reasonable consensus estimate of the highest velocity that could be reached using hydrogen fusion as the means of propulsion?”

As Michael Kelsey said, there is no upper limit, but there is a terrible tradeoff: the longer you want to accelerate for, the more fuel you need to bring. If your fuel is not energy efficient (chemical is worse than nuclear is worse than antimatter), this gets you in trouble quickly. Why? You need to not only accelerate your payload, but all the remaining fuel you have on board. This is why rockets jettison their used-up stages, so you don’t have to keep accelerating all that mass. There’s no technical limit for the speed you can reach (or the amount of time you can accelerate for), but depending on your fuel’s efficiency — and hydrogen fusion is about 0.7% efficient — you’re going to be limited by the mass/size of your initial rocket, fuel included.

Light and ripples in space; as the light passes through non-flat space, it changes how an observer at any other location perceives the passage of time for the light. Image credit: European Gravitational Observatory, Lionel BRET/EUROLIOS.

From ketchup on how we talk about time in the expanding Universe: “You mean the merger was detected on September 14th, 2015. Since it happened over a billion light years away, and gravitational waves travel at the speed of light, the merger itself was hundreds of millions of years ago.”

We have a lot of conventions in astronomy, and many of them make people unhappy. Which is unsurprising, since a convention in how we refer to things is a choice, and not everyone has the same personal preferences. Since there are no such things as absolute space or time, however, we talk about the arrival of the first signal of the “event” as when the event occurred.

Two merging black holes, particularly in the final stages of merger, emit tremendous amounts of gravitational waves. Image Credit: SXS, the Simulating eXtreme Spacetimes (SXS) project (http://ift.tt/10eTU31).

For these black holes that created LIGO’s first event, the merger did occur some billion+ years ago; the gravitational waves traveled through space for all that time; they arrived on Earth about 16 months ago; we detected them as soon as they arrived. But when we talk about when the event occurred, we’ll conventionally say it occurred the moment it was detected. Measurements of the CMB are occurring right now, and we can talk about the CMB “today,” even though the light is from 13.8 billion years ago. It’s not right or wrong to make a different choice, but this is how people talk about this.

How single stars end their lives, depending on initial mass. Image credit: A. Heger et al., 2003, via http://ift.tt/2iVS9FH

From Wow on IMBHs (intermediate mass black holes): “A black hole loses MOST of its mass in ejection during the supernova. A 60 solar mass star may form a 6 solar mass black hole. […] Therefore to get to mid size, a black hole has to accrete the extra matter.”

Kind of. If you form a massive enough star (or a metal-free-enough star that’s modestly heavy), you can get a direct black hole, where 100% of the star’s mass becomes a black hole. Intermediate mass black holes, however, are outstanding candidates for dynamically relaxing and heading towards the galactic center, where they contribute to the merger and growth of the central, supermassive behemoths present. If you want to look for them, the best place is within the central few hundred parsecs of a galactic center, and we expect to find many between, say, 20 and a few hundred thousand solar masses. The large black holes found by LIGO’s first detected merger — 36 + 29 becomes 62 solar masses — were the first black holes robustly found in this mass range.

A clumpy dark matter halo with varying densities and a very large, diffuse structure, as predicted by simulations, with the luminous part of the galaxy shown for scale. Image credit: NASA, ESA, and T. Brown and J. Tumlinson (STScI).

From Omega Centauri on dark matter and star wars: “I realized a couple of weeks back, watching “A New Hope”, that the Jedi knew of dark matter a long time ago. ObiOne (sic) describing the force “it binds the galaxies together…””

Dark matter does surround us, it does penetrate us, and it does bind the galaxy together. But unless we can figure out how to coax it into interacting with either itself or some form of matter in a way that goes beyond standard gravitation, we’re never going to directly detect it. Or, you know, use it to move material objects or choke an incompetent Captain.

Albert Einstein in 1920. Image credit: “The Solar Eclipse of May 29, 1919, and the Einstein Effect,” The Scientific Monthly 10:4 (1920), 418-422, on p. 418. Public domain.

From Amos Dettenville on Einstein’s blunders: “I think the first item on your list is wrong. You do a dis-service to your readers by contributing to the spread of the erroneous claims of Ives (anti-relativity crank) and Ohanian, et al. Genuine scholars like Stachel and Torretti long ago debunked the mistaken ideas that you’ve repeated in your Forbes article. For a good recent overview of the facts, see http://ift.tt/2iVZ1mA.”

There is a colorful history of this controversy, that involves anti-semitism, relativity denialism, but also some genuine flaws and incomplete analysis/understanding in the early days. As is usually, the case, I was aware of some of it (Ives, Hasenöhrl) but not all of it (the Field paper). What I said in the article, that I believe still holds up, is:

Einstein was only able to derive E = mc^2 for a particle completely at rest. Despite also inventing special relativity — founded on the principle that the laws of physics are independent of an observer’s frame of reference — Einstein’s formulation couldn’t account for how energy worked for a particle in motion. In other words, E = mc^2 as derived by Einstein was frame-dependent!

The big advance of von Laue, which I think deserves a ton of credit, is that in 1911, he was the first to realize that inertial mass doesn’t mean what it does in classical (Newtonian) mechanics. Around 1911, von Laue made a formulation of a flow of continuous matter in special relativity. “Mass” doesn’t fully characterize the inertial behavior of an extended physical system, and that’s the incompleteness of Einstein’s E = mc^2. Max von Laue made it clear that you need, at minimum, 10 functions, which would become the 10 independent components of the stress-energy tensor in General Relativity. The story I’m most familiar with comes from this book, which is an incredibly informative look at the original source material.

The particles and forces of the Standard Model. Image credit: Contemporary Physics Education Project / DOE / NSF / LBNL, via http://cpepweb.org/.

From Lloyd Hargrove on questionable quotables: “Aleister Crowley? Really?”

Even people who we otherwise dislike, for whatever reasons, may make some amazing statements of wisdom. I have quoted Oprah, Aquinas, Ken Ham and Crowley, among others, and won’t stop quoting someone who says something interesting or thought-provoking just because they say or believe other things that I think are insane. The Crowley quote, by the way, was:

The joy of life consists in the exercise of one’s energies, continual growth, constant change, the enjoyment of every new experience. To stop means simply to die. The eternal mistake of mankind is to set up an attainable ideal.

Large scale projection through the Illustris volume at z=0, centered on the most massive cluster, 15 Mpc/h deep. Shows dark matter density (left) transitioning to gas density (right). The large-scale structure of the Universe cannot be explained without dark matter. Image credit: Illustris Collaboration / Illustris Simulation, via http://ift.tt/1mDBler.

And finally, from Mark Thomas on our finely-tuned Universe: “If ‘initial conditions’ are very close it will not produce an exact outcome of our Universe but a similar 4 dimensional Standard Model Universe with near similar dimensionless constants. To obtain the very exact same ‘initial conditions’ which would produce an exact replica of our Universe might be very improbable. This might produce a vast array of similar Universes as the ‘initial condition’ spectrum may be very large.”

One of the interesting questions one can ask ourselves is how close the Universe needs to be to our own to give a similar Universe. If you vary some of the fundamental constants by a small amount, you’ll get a Universe that’s only slightly different from our own, and where intelligent life is possible. But other constants could vary by a little — or if you vary the wrong constant by just enough — and that will ruin everything! There is an incredible book that I’ve just started reading that addresses this very concept: A Fortunate Universe by Geraint Lewis and Luke Barnes. In fact, maybe I’ll finish it and do a review sometime soon.

In any case, hope your new year is off to a great start and hope that 2017 is full of happiness, wellness and fulfillment for all of you!

from ScienceBlogs http://ift.tt/2iVU5hm

2017 has 2 Friday the 13ths

Image via Kelli Marshall

January 13, 2017 is a Friday, ushering the first of two Friday the 13ths in 2017. Any calendar year has at least one Friday the 13th, but no more than three Friday the 13ths. The last time we had only one Friday the 13th in a calendar year was in May 2016 and the next time won’t be until August 2021. Three Friday the 13ths last took place in 2015 (February, March, November), and will next happen in 2026. This year, in 2017, there are two Friday the 13ths (January and October).

Not that we at EarthSky suffer from friggatriskaidekaphobia – an irrational fear of Friday the 13th – but, gosh darn, this year’s first Friday the 13th on January 13, 2017 happens exactly 39 weeks (3 x 13 weeks) before the next Friday the 13th in October 2017. But that’s hardly the end of it. Next year, in 2018 (which also has two Friday the 13ths), the first of the two comes on April 13, 2018, exactly 26 weeks (2 x 13 weeks) after the Friday the 13th in October 2017. Then the second Friday the 13th of 2018 falls on July 13, 2018, exactly 13 weeks after the Friday the 13th in April 2018.

Yikes, that’s quite a few of coincidences involving the number 13 … though we could cite many more!

Follow the links below to learn more about why some people fear this day and about the intriguing numerology of Friday the 13th and the calendar.

Scary coincidence or super unlucky?

In 2017, blame a common year starting on Sunday

How often do January-October Friday the 13ths happen?

Rhyme and reason for the 400-year Friday the 13th cycle

Gregoriana cycle of 372 years

Can a leap year start on Sunday?

Gioachino Rossini, a 19th century Italian composer. Folklorists say there's no written evidence that Friday the 13th was considered unlucky before the 19th century. The earliest known documented reference in English appears to be in Henry Sutherland Edwards' 1869 biography of Rossini.

Scary coincidence or super unlucky? Neither. It’s just a quirk of our calendar, as you’ll see as you keep reading.

The fact is that, according to folklorists, there’s no written evidence that Friday the 13th was considered unlucky before the 19th century. The earliest known documented reference in English appears to be in Henry Sutherland Edwards’ 1869 biography of Gioachino Rossini. His portrait is on this page. He doesn’t look scary.

Friday has always gotten a bad rap. In the Middle Ages, people would not marry – or set out on a journey – on a Friday.

There are also some links between Christianity and an ill association with either Fridays or the number 13. Jesus was said to be crucified on a Friday. Seating 13 people at a table was seen as bad luck because Judas Iscariot, the disciple who betrayed Jesus, is said to have been the 13th guest at the Last Supper. Meanwhile, our word for Friday comes from Frigga, an ancient Scandinavian fertility and love goddess. Christians called Frigga a witch and Friday the witches’ Sabbath.

In modern times, the slasher-movie franchise Friday the 13th has helped keep friggatriskaidekaphobia alive.

Best New Year’s gift ever! EarthSky moon calendar for 2017

Enjoying EarthSky so far? Sign up for our free daily newsletter today!

The Friday the 13th slasher-movie franchise helped keep this day maintain its notoriety. Image via Wikimedia Commons

In 2017, blame a common year starting on Sunday. Whenever a common year of 365 days starts on a Sunday, it’s inevitable that the months of January and October will start on a Sunday. And any month starting on a Sunday always has a Friday the 13th. So this year, in 2017, we’ll have a Friday the 13th in January and October.

The last time a common year started on a Sunday was 11 years ago, in the year 2006. The next time will be six years from 2017, in 2023. Some of you may wonder if there’s some formula that governs how this twofold Friday the 13th drama repeats itself. The answer is a definite yes. Keep in mind that this January-October Friday the 13th year can only happen in a common year of 365 days, and when January 1 falls on a Sunday.

Any calendar year that happens one year after a leap year will recur in 6, 17 and 28 years. Therefore, if our twofold Friday the 13th year comes one year after a leap year, as it does in 2017, the days and dates will match up again in 6, 17 and 28 years. Therefore, the years 2023, 2034 and 2045 will all harbor January and October Friday the 13ths:

2017 + 6 = 2023

2017 + 17 = 2034

2017 + 28 = 2045

Calendar for 2017

Calendar for 2017 via TimeandDate.com.

How often do January-October Friday the 13ths happen? More often than you might imagine! The first January-October Friday the 13th year in the 21st century (2001 to 2100) occurred in 2006, which is two years after a leap year. Any calendar year happening two years after a leap year will have days and dates matching up again in periods of 11, 17 and 28 years:

2006 + 11 = 2017

2006 + 17 = 2023

2006 + 28 = 2034

We continue the cycle onward to find a grand total of 10 January-October Friday the 13th years for the 21st century (2001 to 2100):

2006, 2017, 2023, 2034, 2045, 2051, 2062, 2073, 2079 and 2090

Because the year 2090 is two years after a leap year, we might be tempted to project the next January-October Friday the 13th to the year 2101:

2090 + 11 = 2101

Alas, here’s where the Gregorian calendar throws a monkey wrench at us. By Gregorian calendar rules, century years not equally divisible by 400 (e.g. 2100, 2200, 2300) are not leap years of 366 days – but rather, common years of 365 days. So the suppression of the leap year in 2100 perturbs the cycle, bringing about the first January-October Friday the 13th year of the 22nd century (2101 to 2200) in the year 2102, instead of 2101.

By good fortune, we can pretend that the year 2102 comes two years after a leap year, to project the recurrence of January-October Friday the 13th years in periods of 11, 17 and 28 years.

2102 + 11 = 2113

2102 + 17 = 2119

2102 + 28 = 2130

We continue the cycle onward to find a total of 11 January-October Friday the 13th years for the 22nd century (2100 to 2200):

2102, 2113, 2119, 2130, 2141, 2147, 2158, 2169, 2175, 2186 and 2192

In the 23rd century (2201 to 2300), the cycle is perturbed again. The first January-October Friday the 13th year does not fall in 2203 – but rather in 2209, which is one year after a leap year. Any calendar year happening one year after a leap year recurs in 6, 17 and 28 years.

Thus, we find 11 January-October Friday the 13th years for the 23rd century (2201 to 2300):

2209, 2215, 2226, 2237, 2243, 2254, 2265, 2271, 2282, 2293 and 2299

In the 24th century (2301 to 2400), the cycle is again perturbed. The first January-October Friday the 13th year does not come in 2310 – but rather in 2305, or one year after a leap year. That gives 11 January-October Friday the 13th years for the 24th century (2301 to 2400):

2305, 2311, 2322, 2333, 2239, 2350, 2361, 2367, 2378, 2389 and 2395

Because the year 2400 IS a leap year of 366 days, the cycle is NOT perturbed in the following 25th century (2401 to 2500). So we can keep on going to find 10 January-October Friday the 13th years for the 25th century (2401 to 2500).

2406, 2417, 2423, 2434, 2445, 2451, 2462, 2473, 2479 and 2490

Statistically speaking … the modal day for the 13th to occur on is Friday, with 688 occurrences in the 4,800-month cycle. (Of course, this is the same graph for the 6th as well as the 13th, 20th and 27th.) Caption and graphic via datagenetics.com.

Rhyme and reason for the 400-year Friday the 13th cycle.

Because the Gregorian calendar has a 400-year cycle, the January-October Friday the 13th years recur in cycles of 400 years. For example, respective January-October Friday the 13th calendar years are exactly 400 years apart in the 21st and 25th centuries:

21st century (2001 to 2100):

2006, 2017, 2023, 2034, 2045, 2051, 2062, 2073, 2079 and 2090

25th century (2401 to 2500):

2406, 2417, 2423, 2434, 2445, 2451, 2462, 2473, 2479 and 2490

Gregoriana cycle of 372 years.

It appears as though cycles of 372 and 400 years (372 + 28) prevail over the long course of centuries. Take the year 2017, for instance:

2017 + 372 = 2389

2017 + 400 = 2417

The 372-year period is known as the Gregoriana eclipse cycle, which we elaborate about in our post: How often does a solar eclipse happen on the March equinox?

As magical as all of this number play seems to be, it’s not supernatural. The Friday the 13th calendar intrigue is simple numerology, even if it forever haunts our uncomprehending minds.

Can a leap year start on Sunday?

Yes, a leap year of 366 days can start on a Sunday. It last occurred in the year 2012 and will next happen in 2040. Any leap year starting on a Sunday has three Friday the 13ths which fall in January, April and July. The days and dates of any leap year match up again in periods of 28 years. So we have only four January-April-July Friday the 13th years in the 21st century (2001 to 2100):

2012, 2040, 2068 and 2096

… and whether or not it is clear to you, the universe is unfolding as it should. Resin, acrylic paint and archival print on transparency on panel, by Boston artist Jessica Dunegan.

Bottom line: Scared of Friday the 13th? It’s just a feature of our Gregorian calendar, and a pretty common one at that. From what we’ve been able to gather, the 400-year cycle displayed by the Gregorian calendar features 688 Friday the 13ths. We find that 43 of these 400 years harbor January-October Friday the 13ths, accounting for 86 of the 688 Friday the 13ths in one 400-year cycle.

2015 had 3 Friday the 13ths. What are the odds?

When does Friday the 13th have a full moon?

from EarthSky http://ift.tt/2ix9hkh

Image via Kelli Marshall

January 13, 2017 is a Friday, ushering the first of two Friday the 13ths in 2017. Any calendar year has at least one Friday the 13th, but no more than three Friday the 13ths. The last time we had only one Friday the 13th in a calendar year was in May 2016 and the next time won’t be until August 2021. Three Friday the 13ths last took place in 2015 (February, March, November), and will next happen in 2026. This year, in 2017, there are two Friday the 13ths (January and October).

Not that we at EarthSky suffer from friggatriskaidekaphobia – an irrational fear of Friday the 13th – but, gosh darn, this year’s first Friday the 13th on January 13, 2017 happens exactly 39 weeks (3 x 13 weeks) before the next Friday the 13th in October 2017. But that’s hardly the end of it. Next year, in 2018 (which also has two Friday the 13ths), the first of the two comes on April 13, 2018, exactly 26 weeks (2 x 13 weeks) after the Friday the 13th in October 2017. Then the second Friday the 13th of 2018 falls on July 13, 2018, exactly 13 weeks after the Friday the 13th in April 2018.

Yikes, that’s quite a few of coincidences involving the number 13 … though we could cite many more!

Follow the links below to learn more about why some people fear this day and about the intriguing numerology of Friday the 13th and the calendar.

Scary coincidence or super unlucky?

In 2017, blame a common year starting on Sunday

How often do January-October Friday the 13ths happen?

Rhyme and reason for the 400-year Friday the 13th cycle

Gregoriana cycle of 372 years

Can a leap year start on Sunday?

Gioachino Rossini, a 19th century Italian composer. Folklorists say there's no written evidence that Friday the 13th was considered unlucky before the 19th century. The earliest known documented reference in English appears to be in Henry Sutherland Edwards' 1869 biography of Rossini.

Scary coincidence or super unlucky? Neither. It’s just a quirk of our calendar, as you’ll see as you keep reading.

The fact is that, according to folklorists, there’s no written evidence that Friday the 13th was considered unlucky before the 19th century. The earliest known documented reference in English appears to be in Henry Sutherland Edwards’ 1869 biography of Gioachino Rossini. His portrait is on this page. He doesn’t look scary.

Friday has always gotten a bad rap. In the Middle Ages, people would not marry – or set out on a journey – on a Friday.

There are also some links between Christianity and an ill association with either Fridays or the number 13. Jesus was said to be crucified on a Friday. Seating 13 people at a table was seen as bad luck because Judas Iscariot, the disciple who betrayed Jesus, is said to have been the 13th guest at the Last Supper. Meanwhile, our word for Friday comes from Frigga, an ancient Scandinavian fertility and love goddess. Christians called Frigga a witch and Friday the witches’ Sabbath.

In modern times, the slasher-movie franchise Friday the 13th has helped keep friggatriskaidekaphobia alive.

Best New Year’s gift ever! EarthSky moon calendar for 2017

Enjoying EarthSky so far? Sign up for our free daily newsletter today!

The Friday the 13th slasher-movie franchise helped keep this day maintain its notoriety. Image via Wikimedia Commons

In 2017, blame a common year starting on Sunday. Whenever a common year of 365 days starts on a Sunday, it’s inevitable that the months of January and October will start on a Sunday. And any month starting on a Sunday always has a Friday the 13th. So this year, in 2017, we’ll have a Friday the 13th in January and October.

The last time a common year started on a Sunday was 11 years ago, in the year 2006. The next time will be six years from 2017, in 2023. Some of you may wonder if there’s some formula that governs how this twofold Friday the 13th drama repeats itself. The answer is a definite yes. Keep in mind that this January-October Friday the 13th year can only happen in a common year of 365 days, and when January 1 falls on a Sunday.

Any calendar year that happens one year after a leap year will recur in 6, 17 and 28 years. Therefore, if our twofold Friday the 13th year comes one year after a leap year, as it does in 2017, the days and dates will match up again in 6, 17 and 28 years. Therefore, the years 2023, 2034 and 2045 will all harbor January and October Friday the 13ths:

2017 + 6 = 2023

2017 + 17 = 2034

2017 + 28 = 2045

Calendar for 2017

Calendar for 2017 via TimeandDate.com.

How often do January-October Friday the 13ths happen? More often than you might imagine! The first January-October Friday the 13th year in the 21st century (2001 to 2100) occurred in 2006, which is two years after a leap year. Any calendar year happening two years after a leap year will have days and dates matching up again in periods of 11, 17 and 28 years:

2006 + 11 = 2017

2006 + 17 = 2023

2006 + 28 = 2034

We continue the cycle onward to find a grand total of 10 January-October Friday the 13th years for the 21st century (2001 to 2100):

2006, 2017, 2023, 2034, 2045, 2051, 2062, 2073, 2079 and 2090

Because the year 2090 is two years after a leap year, we might be tempted to project the next January-October Friday the 13th to the year 2101:

2090 + 11 = 2101

Alas, here’s where the Gregorian calendar throws a monkey wrench at us. By Gregorian calendar rules, century years not equally divisible by 400 (e.g. 2100, 2200, 2300) are not leap years of 366 days – but rather, common years of 365 days. So the suppression of the leap year in 2100 perturbs the cycle, bringing about the first January-October Friday the 13th year of the 22nd century (2101 to 2200) in the year 2102, instead of 2101.

By good fortune, we can pretend that the year 2102 comes two years after a leap year, to project the recurrence of January-October Friday the 13th years in periods of 11, 17 and 28 years.

2102 + 11 = 2113

2102 + 17 = 2119

2102 + 28 = 2130

We continue the cycle onward to find a total of 11 January-October Friday the 13th years for the 22nd century (2100 to 2200):

2102, 2113, 2119, 2130, 2141, 2147, 2158, 2169, 2175, 2186 and 2192

In the 23rd century (2201 to 2300), the cycle is perturbed again. The first January-October Friday the 13th year does not fall in 2203 – but rather in 2209, which is one year after a leap year. Any calendar year happening one year after a leap year recurs in 6, 17 and 28 years.

Thus, we find 11 January-October Friday the 13th years for the 23rd century (2201 to 2300):

2209, 2215, 2226, 2237, 2243, 2254, 2265, 2271, 2282, 2293 and 2299

In the 24th century (2301 to 2400), the cycle is again perturbed. The first January-October Friday the 13th year does not come in 2310 – but rather in 2305, or one year after a leap year. That gives 11 January-October Friday the 13th years for the 24th century (2301 to 2400):

2305, 2311, 2322, 2333, 2239, 2350, 2361, 2367, 2378, 2389 and 2395

Because the year 2400 IS a leap year of 366 days, the cycle is NOT perturbed in the following 25th century (2401 to 2500). So we can keep on going to find 10 January-October Friday the 13th years for the 25th century (2401 to 2500).

2406, 2417, 2423, 2434, 2445, 2451, 2462, 2473, 2479 and 2490

Statistically speaking … the modal day for the 13th to occur on is Friday, with 688 occurrences in the 4,800-month cycle. (Of course, this is the same graph for the 6th as well as the 13th, 20th and 27th.) Caption and graphic via datagenetics.com.

Rhyme and reason for the 400-year Friday the 13th cycle.

Because the Gregorian calendar has a 400-year cycle, the January-October Friday the 13th years recur in cycles of 400 years. For example, respective January-October Friday the 13th calendar years are exactly 400 years apart in the 21st and 25th centuries:

21st century (2001 to 2100):

2006, 2017, 2023, 2034, 2045, 2051, 2062, 2073, 2079 and 2090

25th century (2401 to 2500):

2406, 2417, 2423, 2434, 2445, 2451, 2462, 2473, 2479 and 2490

Gregoriana cycle of 372 years.

It appears as though cycles of 372 and 400 years (372 + 28) prevail over the long course of centuries. Take the year 2017, for instance:

2017 + 372 = 2389

2017 + 400 = 2417

The 372-year period is known as the Gregoriana eclipse cycle, which we elaborate about in our post: How often does a solar eclipse happen on the March equinox?

As magical as all of this number play seems to be, it’s not supernatural. The Friday the 13th calendar intrigue is simple numerology, even if it forever haunts our uncomprehending minds.

Can a leap year start on Sunday?

Yes, a leap year of 366 days can start on a Sunday. It last occurred in the year 2012 and will next happen in 2040. Any leap year starting on a Sunday has three Friday the 13ths which fall in January, April and July. The days and dates of any leap year match up again in periods of 28 years. So we have only four January-April-July Friday the 13th years in the 21st century (2001 to 2100):

2012, 2040, 2068 and 2096

… and whether or not it is clear to you, the universe is unfolding as it should. Resin, acrylic paint and archival print on transparency on panel, by Boston artist Jessica Dunegan.

Bottom line: Scared of Friday the 13th? It’s just a feature of our Gregorian calendar, and a pretty common one at that. From what we’ve been able to gather, the 400-year cycle displayed by the Gregorian calendar features 688 Friday the 13ths. We find that 43 of these 400 years harbor January-October Friday the 13ths, accounting for 86 of the 688 Friday the 13ths in one 400-year cycle.

2015 had 3 Friday the 13ths. What are the odds?

When does Friday the 13th have a full moon?

from EarthSky http://ift.tt/2ix9hkh

Trump Calls The Majority Who Voted Against Him Enemies And Losers In New Year’s Message? [Stoat]

More politics-via-fb I’m afraid. I wouldn’t trouble you with this except people I know not only post it, but defend it. My headline could instead have been “a plea for toleration”. Some… oh dear, I’m pleading for toleration, aren’t I? So I’d better be nice and choose my words with care. Some website, “politicususa.com” wrote:

President-elect Trump delivered a bizarre New Year’s message where he claimed that the majority of voters who voted against him are his enemies and losers.

Trump is indeed something of a loose cannon and I wouldn’t have been especially surprised to see that he had done this; but it’s always a good idea to check what was actually said; almost invariably paraphrases turn out to be inaccurate, especially when done by people who don’t like the paraphrasee. What Trump actually said was

Happy New Year to all, including to my many enemies and those who have fought me and lost so badly they just don’t know what to do. Love!

Now I’d be happy to argue this is unpresidential and tasteless but does it claim that “the majority of voters who voted against him are his enemies”? No, of course not. It is directed against “enemies” and “those who have fought me” – clearly something far more active in terms of opposition is meant; simply voting against him doesn’t make you his “enemy” nor is it sufficiently significant to count as fighting. Quite apart from that, the basic logic of the claim is also wrong: even if you were to accept the (in my view implausible) claim that “those who have fought me and lost” include those that voted against him, it still doesn’t call those people his enemies; the conjunctive “and” just doesn’t work like that; if it were a ” – ” instead that might be different¹

As if to demonstrate a pattern of falsehood the article continues The reality is that the people who voted against Trump know exactly what to do… which is manifestly false. The opposition to Trump exists but it is scattered and confused and is (in my opinion) wildly running around like headless chickens trying to work out a coherent strategy.

So what is this stuff for? It is there to polarise debate. To convince those that voted against Trump that he is actively their enemy. And therefore to rally them around <someone’s> banner. And these are just the same people who will complain bitterly about how polarised the political debate is (yes, I know. In terms of the GW debate I’m not exactly a shining example of non-polarisation. Perhaps I should think about that a bit).

Notes

1. There are, of course, two theories about Trump’s tweets. The first – probably correct, since simplest – is that they are exactly what they appear to be: rather hastily constructed, not always well thought about, and certainly not checked by third parties before publication. The second is that it is all a cunning trick to say carefully pre-meditated outrageous things in public and get away with it. But if the first theory is correct then a careful exact parsing of the tweet is inappropriate.

from ScienceBlogs http://ift.tt/2iVsEEe

More politics-via-fb I’m afraid. I wouldn’t trouble you with this except people I know not only post it, but defend it. My headline could instead have been “a plea for toleration”. Some… oh dear, I’m pleading for toleration, aren’t I? So I’d better be nice and choose my words with care. Some website, “politicususa.com” wrote:

President-elect Trump delivered a bizarre New Year’s message where he claimed that the majority of voters who voted against him are his enemies and losers.

Trump is indeed something of a loose cannon and I wouldn’t have been especially surprised to see that he had done this; but it’s always a good idea to check what was actually said; almost invariably paraphrases turn out to be inaccurate, especially when done by people who don’t like the paraphrasee. What Trump actually said was

Happy New Year to all, including to my many enemies and those who have fought me and lost so badly they just don’t know what to do. Love!

Now I’d be happy to argue this is unpresidential and tasteless but does it claim that “the majority of voters who voted against him are his enemies”? No, of course not. It is directed against “enemies” and “those who have fought me” – clearly something far more active in terms of opposition is meant; simply voting against him doesn’t make you his “enemy” nor is it sufficiently significant to count as fighting. Quite apart from that, the basic logic of the claim is also wrong: even if you were to accept the (in my view implausible) claim that “those who have fought me and lost” include those that voted against him, it still doesn’t call those people his enemies; the conjunctive “and” just doesn’t work like that; if it were a ” – ” instead that might be different¹

As if to demonstrate a pattern of falsehood the article continues The reality is that the people who voted against Trump know exactly what to do… which is manifestly false. The opposition to Trump exists but it is scattered and confused and is (in my opinion) wildly running around like headless chickens trying to work out a coherent strategy.

So what is this stuff for? It is there to polarise debate. To convince those that voted against Trump that he is actively their enemy. And therefore to rally them around <someone’s> banner. And these are just the same people who will complain bitterly about how polarised the political debate is (yes, I know. In terms of the GW debate I’m not exactly a shining example of non-polarisation. Perhaps I should think about that a bit).

Notes

1. There are, of course, two theories about Trump’s tweets. The first – probably correct, since simplest – is that they are exactly what they appear to be: rather hastily constructed, not always well thought about, and certainly not checked by third parties before publication. The second is that it is all a cunning trick to say carefully pre-meditated outrageous things in public and get away with it. But if the first theory is correct then a careful exact parsing of the tweet is inappropriate.

from ScienceBlogs http://ift.tt/2iVsEEe