Consensus on consensus hits half a million downloads

In 2013, the Skeptical Science team published a study in Environmental Research Letters finding 97% scientific consensus on human-caused global warming. However, we weren't the first researchers to find overwhelming scientific consensus, nor were we the last. In 2016, we teamed up with authors of six other consensus studies to publish Consensus on consensus: a synthesis of consensus estimates on human-caused global warming. This week, our Consensus on Consensus study just went past 500,000 downloads.

Replication is the heart of the scientific method. When multiple scientific studies, using independent methods, all arrive at similar conclusions, we become more confident that our scientific understanding is correct. This is why scientists are so confident that humans are causing global warming: multiple lines of evidence all find human fingerprints in climate change. In the same way, we know there is a scientific consensus because multiple studies independently find overwhelming scientific agreement that humans are causing global warming.

So I was always bemused by the fact that our 2013 consensus study received so many attacks, as if this would singlehandedly overturn the 97% consensus on human-caused global warming. This sentiment is most explicitly articulated by Senator Ted Cruz who argued that the 97% consensus was based "on one bogus study." The simplest retort to this argument is that the 97% consensus has been confirmed by multiple studies, including Doran & Zimmerman 2009, Anderegg et al 2010, and Carlton et al. 2015.

So imagine our surprise when Richard Tol, who threw critique after critique at our 2013 consensus study, unveiled a new line of attack: our 97% consensus was an outlier compared to other studies. This was a valiant attempt at ju jitsu, turning the strongest element of our research (consistency with independent studies) into a potential weakness (claiming our research conflicted with other studies). However, in order to make this argument, Tol misrepresented the other consensus studies beyond recognition, much to the indignation of the authors of those studies.

While Tol's egregious misinformation is problematic, it did inspire the authors of seven leading consensus studies to collaborate on the Consensus on consensus study. We summarized the level of agreement among climate scientists on climate change - establishing that no matter how you approach it, there is overwhelming agreement that humans are causing global warming. And now that the study has been downloaded a half million times, you could argue that Tol's efforts have led to raising awareness of the robust nature of the consensus on climate change.

The other important contribution of Consensus on consensus was shining disinfecting sunlight on a common strategy used to cast doubt on expert consensus: the fake expert technique. This involves citing people who convey the impression of expertise but don't possess the relevant expertise on a specific scientific matter. The tobacco industry perfected this technique in advertisements citing general scientists, doctors, or educators - people who convey the impression of expertise but have never actually researched the health impacts of smoking.

In Consensus on consensus, we showed that agreement on human-caused global warming increases with expertise in climate science. This means that if one cherry picks sub-groups of scientists with less expertise in climate change (e.g., economic geologists), you can obtain lower levels of agreement. When you hear of a scientific group with low levels of agreement on human-caused global warming, this group consists of fake experts. Tol used this technique by selecting sub-groups of non-climate-experts from various consensus studies, to argue that they found lower consensus than 97%.

While much of my research has been spent on quantifying the consensus, even more of my work has focused on communicating the consensus. Two of my experimental studies, Rational Irrationality and Neutralizing misinformation through inoculation, demonstrated how effective communicating the scientific consensus is in raising awareness of the reality of climate change and neutralizing misinformation. However, these two studies are only two amongst a much larger body of evidence confirming the efficacy of communicating the consensus. This is why I created a Consensus on Consensus Messaging post summarizing the research into consensus communication. Communicating the consensus is an important part of raising climate literacy and building public support for climate action.

from Skeptical Science https://ift.tt/2zN92Zm

In 2013, the Skeptical Science team published a study in Environmental Research Letters finding 97% scientific consensus on human-caused global warming. However, we weren't the first researchers to find overwhelming scientific consensus, nor were we the last. In 2016, we teamed up with authors of six other consensus studies to publish Consensus on consensus: a synthesis of consensus estimates on human-caused global warming. This week, our Consensus on Consensus study just went past 500,000 downloads.

Replication is the heart of the scientific method. When multiple scientific studies, using independent methods, all arrive at similar conclusions, we become more confident that our scientific understanding is correct. This is why scientists are so confident that humans are causing global warming: multiple lines of evidence all find human fingerprints in climate change. In the same way, we know there is a scientific consensus because multiple studies independently find overwhelming scientific agreement that humans are causing global warming.

So I was always bemused by the fact that our 2013 consensus study received so many attacks, as if this would singlehandedly overturn the 97% consensus on human-caused global warming. This sentiment is most explicitly articulated by Senator Ted Cruz who argued that the 97% consensus was based "on one bogus study." The simplest retort to this argument is that the 97% consensus has been confirmed by multiple studies, including Doran & Zimmerman 2009, Anderegg et al 2010, and Carlton et al. 2015.

So imagine our surprise when Richard Tol, who threw critique after critique at our 2013 consensus study, unveiled a new line of attack: our 97% consensus was an outlier compared to other studies. This was a valiant attempt at ju jitsu, turning the strongest element of our research (consistency with independent studies) into a potential weakness (claiming our research conflicted with other studies). However, in order to make this argument, Tol misrepresented the other consensus studies beyond recognition, much to the indignation of the authors of those studies.

While Tol's egregious misinformation is problematic, it did inspire the authors of seven leading consensus studies to collaborate on the Consensus on consensus study. We summarized the level of agreement among climate scientists on climate change - establishing that no matter how you approach it, there is overwhelming agreement that humans are causing global warming. And now that the study has been downloaded a half million times, you could argue that Tol's efforts have led to raising awareness of the robust nature of the consensus on climate change.

The other important contribution of Consensus on consensus was shining disinfecting sunlight on a common strategy used to cast doubt on expert consensus: the fake expert technique. This involves citing people who convey the impression of expertise but don't possess the relevant expertise on a specific scientific matter. The tobacco industry perfected this technique in advertisements citing general scientists, doctors, or educators - people who convey the impression of expertise but have never actually researched the health impacts of smoking.

In Consensus on consensus, we showed that agreement on human-caused global warming increases with expertise in climate science. This means that if one cherry picks sub-groups of scientists with less expertise in climate change (e.g., economic geologists), you can obtain lower levels of agreement. When you hear of a scientific group with low levels of agreement on human-caused global warming, this group consists of fake experts. Tol used this technique by selecting sub-groups of non-climate-experts from various consensus studies, to argue that they found lower consensus than 97%.

While much of my research has been spent on quantifying the consensus, even more of my work has focused on communicating the consensus. Two of my experimental studies, Rational Irrationality and Neutralizing misinformation through inoculation, demonstrated how effective communicating the scientific consensus is in raising awareness of the reality of climate change and neutralizing misinformation. However, these two studies are only two amongst a much larger body of evidence confirming the efficacy of communicating the consensus. This is why I created a Consensus on Consensus Messaging post summarizing the research into consensus communication. Communicating the consensus is an important part of raising climate literacy and building public support for climate action.

from Skeptical Science https://ift.tt/2zN92Zm

Will the Webb telescope be able to detect life signs at nearby exoplanets?

Artist’s concept of the James Webb Space Telescope as it’ll appear once it’s launched to Earth-orbit in 2021. Want to see how the actual telescope looks now? See the bottom of this post. Image via Northrop Grumman/JWST.

Only 39 light-years from Earth – right next door, cosmically-speaking – there’s a solar system with seven Earth-sized rocky planets. The system is called TRAPPIST-1. All of its seven planets are intriguing, and three of them orbit in their star’s habitable zone, where temperatures could allow liquid water to exist on them.

These worlds have been the subject of much study in the past few years, but there are limits to what current telescopes can learn more about them. What’s more, there’s been a debate about whether the James Webb Space Telescope – Hubble’s successor, scheduled for launch in March of 2021 – will be powerful enough to detect life signs at the distance of these Earth-sized planets, if indeed life signs do exist there. But now a new study says, yes, the Webb will be able to analyze their atmospheres for biosignatures. What’s more, the study says, this analysis could be done in only a year, although clouds in the planets’ atmospheres might pose a problem.

The new paper was first published on June 21, 2019 in The Astronomical Journal, and the study was led by Jacob Lustig-Yaeger, an astronomy student at the University of Washington.

According to Lustig-Yaeger:

The Webb telescope has been built, and we have an idea how it will operate. We used computer modeling to determine the most efficient way to use the telescope to answer the most basic question we’ll want to ask, which is: Are there even atmospheres on these planets, or not?

Artist’s concept of the 7 Earth-sized exoplanets in the TRAPPIST-1 planetary system. Image via R. Hurt/T. Pyle/NASA/JPL-Caltech/WOSU.

All seven of the known planets in the TRAPPIST-1 system are rocky, and of a similar size to Earth. They all orbit close to their star, but since the star a red dwarf and cooler than the sun, that means that three of the planets are still in the star’s habitable zone, where temperatures could make liquid water possible, depending on other factors such as type of atmosphere. It is expected that most or all of the planets have atmospheres, but that isn’t known for certain yet. The Webb telescope will be able to confirm that, and analyze those atmospheres for possible biosignatures, gases like oxygen or methane that could indicate life on the surfaces. According to Lustig-Yaeger:

There is a big question in the field right now whether these planets even have atmospheres, especially the innermost planets. Once we have confirmed that there are atmospheres, then what can we learn about each planet’s atmosphere, the molecules that make it up?

The study suggests that the Webb telescope should be able to detect and analyze any atmospheres fairly quickly, in a year or so. Since the planets are all close to their star, that means their transit times – the time it takes for a planet to cross in front of its star from our viewpoint – are relatively short. The Webb should be able to confirm the atmospheres (or not) in 10 transits or less.

Artist’s concept of TRAPPIST-1e, which scientists think has the best chance of having a habitable atmosphere and an ocean like Earth. Image via NOAA/Inverse.

This does also, however, depend on whether those atmospheres have clouds. If a planet had a thick cloudy atmosphere like Venus,  it could take up to 30 transits to confirm it. So the Webb telescope could still do it, it would just take longer, Lustig-Yaeger said:

But that is still an achievable goal. It means that even in the case of realistic high-altitude clouds, the James Webb telescope will still be capable of detecting the presence of atmospheres, which before our paper was not known.

The James Webb Space Telescope’s capability of detecting the atmospheres of smaller rocky planets is exciting, since other telescopes haven’t been able to yet. It’s a lot easier with gas giant planets like Jupiter, but difficult with smaller planets when they are so far away.

Another possibility is that the Webb will find evidence of water that the planets lost when the system was much younger and the star was much hotter. In such cases, an atmosphere could contain abiotic oxygen – not created by life – that might be a false positive signal of active biology. Scientists would need to determine if the oxygen is biotic or abiotic.

Artist’s concept of the surface of TRAPPIST-1f. Image via Inverse.

The James Webb Space Telescope will be invaluable for studying rocky planets like Earth, astronomers say, and many more of these rocky worlds are being discovered all the time in the vast space of our Milky Way galaxy. It is estimated that there are billions of such worlds in our galaxy alone, and the Webb might provide the first compelling evidence for life on one (or more) of them. Even if it doesn’t, though, it will help to revolutionize our understanding of these planets. As noted by astronomy doctoral student Andrew Lincowski:

By doing this study, we have looked at: What are the best-case scenarios for the James Webb Space Telescope? What is it going to be capable of doing? Because there are definitely going to be more Earth-sized planets found before it launches in 2021.

The TRAPPIST-1 planetary system is unique among such systems as known so far, with seven Earth-sized exoplanets. Could any of them have life? They are ideal candidates for further study by the Webb, which may be able to help answer that intriguing question in the relatively near future. As Lustig-Yaeger added:

It’s hard to conceive in theory of a planetary system better suited for James Webb than TRAPPIST-1.

On August 28, 2019, NASA announced that the two halves of the James Webb Space Telescope have now been successfully connected. The telescope is being assembled at Northrop Grumman’s facilities in Redondo Beach, California. Read more.

Bottom line: For the first time, scientists will be able to study the atmospheres of the seven Earth-sized exoplanets in the TRAPPIST-1 system, using the James Webb Space Telescope, Hubble’s successor, due to launch in 2021.

Source: The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST

Via UW News

from EarthSky https://ift.tt/2UoTQv3

Artist’s concept of the James Webb Space Telescope as it’ll appear once it’s launched to Earth-orbit in 2021. Want to see how the actual telescope looks now? See the bottom of this post. Image via Northrop Grumman/JWST.

Only 39 light-years from Earth – right next door, cosmically-speaking – there’s a solar system with seven Earth-sized rocky planets. The system is called TRAPPIST-1. All of its seven planets are intriguing, and three of them orbit in their star’s habitable zone, where temperatures could allow liquid water to exist on them.

These worlds have been the subject of much study in the past few years, but there are limits to what current telescopes can learn more about them. What’s more, there’s been a debate about whether the James Webb Space Telescope – Hubble’s successor, scheduled for launch in March of 2021 – will be powerful enough to detect life signs at the distance of these Earth-sized planets, if indeed life signs do exist there. But now a new study says, yes, the Webb will be able to analyze their atmospheres for biosignatures. What’s more, the study says, this analysis could be done in only a year, although clouds in the planets’ atmospheres might pose a problem.

The new paper was first published on June 21, 2019 in The Astronomical Journal, and the study was led by Jacob Lustig-Yaeger, an astronomy student at the University of Washington.

According to Lustig-Yaeger:

The Webb telescope has been built, and we have an idea how it will operate. We used computer modeling to determine the most efficient way to use the telescope to answer the most basic question we’ll want to ask, which is: Are there even atmospheres on these planets, or not?

Artist’s concept of the 7 Earth-sized exoplanets in the TRAPPIST-1 planetary system. Image via R. Hurt/T. Pyle/NASA/JPL-Caltech/WOSU.

All seven of the known planets in the TRAPPIST-1 system are rocky, and of a similar size to Earth. They all orbit close to their star, but since the star a red dwarf and cooler than the sun, that means that three of the planets are still in the star’s habitable zone, where temperatures could make liquid water possible, depending on other factors such as type of atmosphere. It is expected that most or all of the planets have atmospheres, but that isn’t known for certain yet. The Webb telescope will be able to confirm that, and analyze those atmospheres for possible biosignatures, gases like oxygen or methane that could indicate life on the surfaces. According to Lustig-Yaeger:

There is a big question in the field right now whether these planets even have atmospheres, especially the innermost planets. Once we have confirmed that there are atmospheres, then what can we learn about each planet’s atmosphere, the molecules that make it up?

The study suggests that the Webb telescope should be able to detect and analyze any atmospheres fairly quickly, in a year or so. Since the planets are all close to their star, that means their transit times – the time it takes for a planet to cross in front of its star from our viewpoint – are relatively short. The Webb should be able to confirm the atmospheres (or not) in 10 transits or less.

Artist’s concept of TRAPPIST-1e, which scientists think has the best chance of having a habitable atmosphere and an ocean like Earth. Image via NOAA/Inverse.

This does also, however, depend on whether those atmospheres have clouds. If a planet had a thick cloudy atmosphere like Venus,  it could take up to 30 transits to confirm it. So the Webb telescope could still do it, it would just take longer, Lustig-Yaeger said:

But that is still an achievable goal. It means that even in the case of realistic high-altitude clouds, the James Webb telescope will still be capable of detecting the presence of atmospheres, which before our paper was not known.

The James Webb Space Telescope’s capability of detecting the atmospheres of smaller rocky planets is exciting, since other telescopes haven’t been able to yet. It’s a lot easier with gas giant planets like Jupiter, but difficult with smaller planets when they are so far away.

Another possibility is that the Webb will find evidence of water that the planets lost when the system was much younger and the star was much hotter. In such cases, an atmosphere could contain abiotic oxygen – not created by life – that might be a false positive signal of active biology. Scientists would need to determine if the oxygen is biotic or abiotic.

Artist’s concept of the surface of TRAPPIST-1f. Image via Inverse.

The James Webb Space Telescope will be invaluable for studying rocky planets like Earth, astronomers say, and many more of these rocky worlds are being discovered all the time in the vast space of our Milky Way galaxy. It is estimated that there are billions of such worlds in our galaxy alone, and the Webb might provide the first compelling evidence for life on one (or more) of them. Even if it doesn’t, though, it will help to revolutionize our understanding of these planets. As noted by astronomy doctoral student Andrew Lincowski:

By doing this study, we have looked at: What are the best-case scenarios for the James Webb Space Telescope? What is it going to be capable of doing? Because there are definitely going to be more Earth-sized planets found before it launches in 2021.

The TRAPPIST-1 planetary system is unique among such systems as known so far, with seven Earth-sized exoplanets. Could any of them have life? They are ideal candidates for further study by the Webb, which may be able to help answer that intriguing question in the relatively near future. As Lustig-Yaeger added:

It’s hard to conceive in theory of a planetary system better suited for James Webb than TRAPPIST-1.

On August 28, 2019, NASA announced that the two halves of the James Webb Space Telescope have now been successfully connected. The telescope is being assembled at Northrop Grumman’s facilities in Redondo Beach, California. Read more.

Bottom line: For the first time, scientists will be able to study the atmospheres of the seven Earth-sized exoplanets in the TRAPPIST-1 system, using the James Webb Space Telescope, Hubble’s successor, due to launch in 2021.

Source: The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST

Via UW News

from EarthSky https://ift.tt/2UoTQv3

Webb telescope now assembled for 1st time

View larger. | Integration teams in a Northrop Grumman clean room in Redondo Beach carefully guide Webb’s suspended telescope section into place. Read more about the Webb’s assembly from NASA

from EarthSky https://ift.tt/2ZFRIQz

View larger. | Integration teams in a Northrop Grumman clean room in Redondo Beach carefully guide Webb’s suspended telescope section into place. Read more about the Webb’s assembly from NASA

from EarthSky https://ift.tt/2ZFRIQz

The Teapot, and the galaxy’s center

Tonight, or on any moonless evening during a Northern Hemisphere summer or Southern Hemisphere winter, you can look in the evening hours toward the center of our Milky Way galaxy. It’s located in the direction of the constellation Sagittarius the Archer, which happens to contain a famous asterism – or noticeable pattern of stars – called the Teapot.

From the Northern Hemisphere, you’ll be looking south during the evening hours for this star pattern. From the Southern Hemisphere, look for the Teapot to climb high overhead around mid-to-late evening.

If you’re blessed with a dark sky, finding all this will be easy. In a dark sky, you’ll see a broad boulevard of stars – the edgewise view into our own Milky Way galaxy – which broadens and brightens in the direction of the galaxy’s center.

Or maybe you know the planets? If you have that dark sky, know that, in 2019, the Teapot is found in between between two bright planets, Saturn to the east and Jupiter to the west. Jupiter is by far the brighter of these two worlds. In fact, it’s the 4th-brightest celestial object to light up the sky, after the sun, moon and the planet Venus. But Venus is now lost in the sun’s glare, so there’s no mistaking Venus for Jupiter in the August 2019 night sky.

Don’t know the planets and don’t have a dark sky? The chart below via AstroBob expands the view to include the constellation Scorpius, which is relatively bright and easy to spot for its curved Scorpion’s Tail. Sagittarius the Archer – and its Teapot asterism – is next door to Scorpius on the sky’s dome.

From the Northern Hemisphere, look southward August and September evenings to see these stars. From the Southern Hemisphere, look generally overhead or northward, higher in the sky and turn this chart upside down. Chart via AstroBob.

We can’t really see the galactic center. It’s heavily veiled by intervening stars, star clusters and nebulae (vast clouds of gas and dust). The center of our Milky Way looms some 26,000 light-years away. But we can gaze toward this direction in space, and – if your sky is dark enough – it’s a sight to behold!

By the way, the Teapot makes up the western half of the constellation Sagittarius the Archer. Modern eyes have an easier time envisioning a teapot than an Archer with a drawn-out bow. See the sky chart of Sagittarius below.

View larger. | The constellation Sagittarius, with the Teapot asterism outlined in green.

From temperate latitudes in the Northern Hemisphere, it’s pretty easy to make out the Summer Triangle asterism rather high in the eastern sky at nightfall. This huge star formation consists of three brilliant stars – Vega, Deneb and Altair – and can oftentimes withstand the glare of the full moon or light-polluted city.

View larger. | Great rift of Milky Way passes through the constellation Cassiopeia and the Summer Triangle. Draw an imaginary line from Deneb through Altair, going about twice the Deneb-Altair distance, to star-hop to the Teapot of Sagittarius

If you are otherwise lost on some starry night but can find the Summer Triangle, let this signpost star formation escort you to the Teapot …

Bottom line: Blessed with a dark sky? Try finding the Teapot in Sagittarius.

Read more: Sagittarius? Here’s your constellation

from EarthSky https://ift.tt/2lSmrMp

Tonight, or on any moonless evening during a Northern Hemisphere summer or Southern Hemisphere winter, you can look in the evening hours toward the center of our Milky Way galaxy. It’s located in the direction of the constellation Sagittarius the Archer, which happens to contain a famous asterism – or noticeable pattern of stars – called the Teapot.

From the Northern Hemisphere, you’ll be looking south during the evening hours for this star pattern. From the Southern Hemisphere, look for the Teapot to climb high overhead around mid-to-late evening.

If you’re blessed with a dark sky, finding all this will be easy. In a dark sky, you’ll see a broad boulevard of stars – the edgewise view into our own Milky Way galaxy – which broadens and brightens in the direction of the galaxy’s center.

Or maybe you know the planets? If you have that dark sky, know that, in 2019, the Teapot is found in between between two bright planets, Saturn to the east and Jupiter to the west. Jupiter is by far the brighter of these two worlds. In fact, it’s the 4th-brightest celestial object to light up the sky, after the sun, moon and the planet Venus. But Venus is now lost in the sun’s glare, so there’s no mistaking Venus for Jupiter in the August 2019 night sky.

Don’t know the planets and don’t have a dark sky? The chart below via AstroBob expands the view to include the constellation Scorpius, which is relatively bright and easy to spot for its curved Scorpion’s Tail. Sagittarius the Archer – and its Teapot asterism – is next door to Scorpius on the sky’s dome.

From the Northern Hemisphere, look southward August and September evenings to see these stars. From the Southern Hemisphere, look generally overhead or northward, higher in the sky and turn this chart upside down. Chart via AstroBob.

We can’t really see the galactic center. It’s heavily veiled by intervening stars, star clusters and nebulae (vast clouds of gas and dust). The center of our Milky Way looms some 26,000 light-years away. But we can gaze toward this direction in space, and – if your sky is dark enough – it’s a sight to behold!

By the way, the Teapot makes up the western half of the constellation Sagittarius the Archer. Modern eyes have an easier time envisioning a teapot than an Archer with a drawn-out bow. See the sky chart of Sagittarius below.

View larger. | The constellation Sagittarius, with the Teapot asterism outlined in green.

From temperate latitudes in the Northern Hemisphere, it’s pretty easy to make out the Summer Triangle asterism rather high in the eastern sky at nightfall. This huge star formation consists of three brilliant stars – Vega, Deneb and Altair – and can oftentimes withstand the glare of the full moon or light-polluted city.

View larger. | Great rift of Milky Way passes through the constellation Cassiopeia and the Summer Triangle. Draw an imaginary line from Deneb through Altair, going about twice the Deneb-Altair distance, to star-hop to the Teapot of Sagittarius

If you are otherwise lost on some starry night but can find the Summer Triangle, let this signpost star formation escort you to the Teapot …

Bottom line: Blessed with a dark sky? Try finding the Teapot in Sagittarius.

Read more: Sagittarius? Here’s your constellation

from EarthSky https://ift.tt/2lSmrMp

September guide to the bright planets

Click the name of a planet to learn more about its visibility in September 2019: Venus, Jupiter, Saturn, Mars and Mercury.

Watch for the moon to pair up with very bright Jupiter around September 5 and fainter, golden Saturn around September 7. Read more. By the way, this chart shows the Northern Hemisphere view, but – from the Southern Hemisphere – the moon is near these same planets on these same approximate dates. For your specific view, try Stellarium Online.

Jupiter – the second-brightest planet after Venus – reigns supreme in the September 2019 night sky. That’s because Venus is sitting close to the glare of sunset all month, leaving dazzling Jupiter to rule the night. Jupiter pops out at dusk – brighter than any star – and stays out until late night. Not sure which one is Jupiter? See the moon in Jupiter’s vicinity for several days, centered on or near September 5. Or just look along the path the sun travels during the day – the ecliptic – for the brightest starlike object you can see. That’ll be Jupiter.

Need more confirmation? Find a bright object you think is Jupiter, steady your binoculars – maybe sit down and anchor them on your knees, or prop your elbows on a fence railing – and aim them at that very bright light. If it is Jupiter, at least one or more of its four largest moons should pop into view.

At mid-northern latitudes in the Northern Hemisphere, Jupiter appears in the south to southwest sky at dusk. In early September, Jupiter sets around midnight (1 a.m. daylight saving time). By midnight, we mean the middle of the night, or midway between sunset and sunrise. By the month’s end, Jupiter sets around 9 p.m. (10 p.m. daylight saving time).

At temperate latitudes in the Southern Hemisphere, Jupiter is found nearly overhead at dusk/nightfall. The king planet sets about an hour after the midnight hour in early September, and then by early October, sets about one hour before midnight.

Try Stellarium Online for the view from your location.

That bright, fiercely twinkling red star – close to Jupiter on our sky’s dome this year – is Antares, the Heart of the Scorpion in the constellation Scorpius. In 2019, sky watchers have been watching Jupiter “wander” east and west relative to this zodiac star. In the first three months of 2019, Jupiter was traveling eastward, away from Antares. Starting on April 10, 2019, Jupiter reversed course, and began moving toward Antares. For four months (April 10 to August 11, 2019), Jupiter traveled in retrograde (or westward), closing the gap between itself and this star. Jupiter is now moving eastward again, away from Antares.

As seen from North America, the moon shines to the west of Saturn on September 7, and then to the east of Saturn on September 8. Read more.

Saturn. After you find Jupiter at dusk and nightfall, use this brilliant beauty of a planet to find another bright evening planet, Saturn. Saturn is not as bright as Jupiter, but the ringed planet shines on par with the sky’s brightest stars. Hold your fist at arm’s length. Saturn is roughly three fist-widths to the east of Jupiter. Because Saturn is the only bright-looking “star” to occupy this part of the sky, you’re not likely to mistake a bright star for Saturn.

Read more: When Jupiter and Saturn meet

Saturn – a golden world to the eye alone – pops out at nightfall and stays out until the wee hours after midnight. This planet – faintest of the major planets visible to the eye in Earth’s sky – still shines as brightly as a 1st-magnitude star, in other words, as brightly as our sky’s brightest stars.

Viewing Saturn’s rings soon? Read me 1st

At mid-northern latitudes, Saturn transits – reaches its highest point for the night – around nightfall. In early September, Saturn sets around one hour after midnight (2 a.m. daylight saving time), and near the month’s end, sets around one hour before midnight (12 a.m. daylight saving time).

At temperate latitudes in the Southern Hemisphere, in early September, Saturn transits – climbs highest up for the night – at early evening, and sets about three hours after the midnight hour. By late September, Saturn transits at evening dusk and sets about one hour after midnight.

You won’t mistake Jupiter for Saturn. Jupiter is significantly brighter than Saturn. Jupiter is the fourth-brightest celestial object after the sun, moon and Venus, respectively, and it outshines Saturn by about 10 times. What’s more, at nightfall and early evening in September 2019, Jupiter shines well to the west of Saturn.

Watch for the bright moon to join up with Saturn around September 7 and 8, as shown on the sky chart above.

At the end of September 2019, it’ll be easier to view the planets Mercury and Venus than it was when this month began. The star Spica – brightest light in the constellation Virgo the Maiden – will be nearby. All of these objects will be easiest to see from Earth’s Southern Hemisphere this month. That’s because the ecliptic – or path of the sun, moon and planets – tilts steeply with respect to the sunset horizon in the autumn, and autumn begins in the Northern Hemisphere on September . Read more.

Mercury and Venus are both nominally evening planets all through September 2019, but both sit way too close to the glare of sunset to be visible at mid-northern latitudes for most of the month. From the Southern Hemisphere, or the northern tropics, you might catch the young moon with both Mercury and Venus near the month’s end, as depicted on the sky chart above.

Note that Venus – the brightest planet – is much brighter than Mercury.

By the way, at Mercury’s most recent inferior conjunction on July 21, 2019, Mercury swung to the south of the sun’s disk as seen from Earth. But when Mercury reaches its next inferior conjunction on November 11, 2019, the innermost planet will swing directly in front of the sun, to stage a transit of Mercury. Transits of Mercury happen more frequently than transits of Venus; they happen 13 or 14 times per century. The last transit of Mercury happened on May 9, 2016, and – after the one on this upcoming November 11 – the next Mercury transit won’t be until November 13, 2032.

You probably won’t see Mars again until late October, 2019. The waning crescent moon will point to Mars on October 23, 24 and 25. On October 26, look for the moon to swing close to Mars on the sky’s dome. Read more.

Where is Mars? Note that the above sky chart is for late October, not September! That’s because late October may feature your first decent chance to catch this world before sunrise. Mars swings on the far side of the sun at superior conjunction on September 2, 2019, to transition from the evening to morning sky. Hiding in the glare of sunrise, Mars probably won’t become visible in the morning sky until late October or November 2019.

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.

Skywatcher, by Predrag Agatonovic.

Bottom line: In September 2019, two planets – Jupiter and Saturn – are easy to see throughout the month. They both come out at nightfall and are out until late night. Mercury and Venus are pretty much lost in the afterglow of sunset, whereas Mars is hiding in the glare of sunrise. Click here for recommended almanacs; they can help you know when the planets rise and set in your sky.

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Visit EarthSky’s Best Places to Stargaze, and recommend a place we can all enjoy.

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Post your planet photos at EarthSky Community Photos

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Click the name of a planet to learn more about its visibility in September 2019: Venus, Jupiter, Saturn, Mars and Mercury.

Watch for the moon to pair up with very bright Jupiter around September 5 and fainter, golden Saturn around September 7. Read more. By the way, this chart shows the Northern Hemisphere view, but – from the Southern Hemisphere – the moon is near these same planets on these same approximate dates. For your specific view, try Stellarium Online.

Jupiter – the second-brightest planet after Venus – reigns supreme in the September 2019 night sky. That’s because Venus is sitting close to the glare of sunset all month, leaving dazzling Jupiter to rule the night. Jupiter pops out at dusk – brighter than any star – and stays out until late night. Not sure which one is Jupiter? See the moon in Jupiter’s vicinity for several days, centered on or near September 5. Or just look along the path the sun travels during the day – the ecliptic – for the brightest starlike object you can see. That’ll be Jupiter.

Need more confirmation? Find a bright object you think is Jupiter, steady your binoculars – maybe sit down and anchor them on your knees, or prop your elbows on a fence railing – and aim them at that very bright light. If it is Jupiter, at least one or more of its four largest moons should pop into view.

At mid-northern latitudes in the Northern Hemisphere, Jupiter appears in the south to southwest sky at dusk. In early September, Jupiter sets around midnight (1 a.m. daylight saving time). By midnight, we mean the middle of the night, or midway between sunset and sunrise. By the month’s end, Jupiter sets around 9 p.m. (10 p.m. daylight saving time).

At temperate latitudes in the Southern Hemisphere, Jupiter is found nearly overhead at dusk/nightfall. The king planet sets about an hour after the midnight hour in early September, and then by early October, sets about one hour before midnight.

Try Stellarium Online for the view from your location.

That bright, fiercely twinkling red star – close to Jupiter on our sky’s dome this year – is Antares, the Heart of the Scorpion in the constellation Scorpius. In 2019, sky watchers have been watching Jupiter “wander” east and west relative to this zodiac star. In the first three months of 2019, Jupiter was traveling eastward, away from Antares. Starting on April 10, 2019, Jupiter reversed course, and began moving toward Antares. For four months (April 10 to August 11, 2019), Jupiter traveled in retrograde (or westward), closing the gap between itself and this star. Jupiter is now moving eastward again, away from Antares.

As seen from North America, the moon shines to the west of Saturn on September 7, and then to the east of Saturn on September 8. Read more.

Saturn. After you find Jupiter at dusk and nightfall, use this brilliant beauty of a planet to find another bright evening planet, Saturn. Saturn is not as bright as Jupiter, but the ringed planet shines on par with the sky’s brightest stars. Hold your fist at arm’s length. Saturn is roughly three fist-widths to the east of Jupiter. Because Saturn is the only bright-looking “star” to occupy this part of the sky, you’re not likely to mistake a bright star for Saturn.

Read more: When Jupiter and Saturn meet

Saturn – a golden world to the eye alone – pops out at nightfall and stays out until the wee hours after midnight. This planet – faintest of the major planets visible to the eye in Earth’s sky – still shines as brightly as a 1st-magnitude star, in other words, as brightly as our sky’s brightest stars.

Viewing Saturn’s rings soon? Read me 1st

At mid-northern latitudes, Saturn transits – reaches its highest point for the night – around nightfall. In early September, Saturn sets around one hour after midnight (2 a.m. daylight saving time), and near the month’s end, sets around one hour before midnight (12 a.m. daylight saving time).

At temperate latitudes in the Southern Hemisphere, in early September, Saturn transits – climbs highest up for the night – at early evening, and sets about three hours after the midnight hour. By late September, Saturn transits at evening dusk and sets about one hour after midnight.

You won’t mistake Jupiter for Saturn. Jupiter is significantly brighter than Saturn. Jupiter is the fourth-brightest celestial object after the sun, moon and Venus, respectively, and it outshines Saturn by about 10 times. What’s more, at nightfall and early evening in September 2019, Jupiter shines well to the west of Saturn.

Watch for the bright moon to join up with Saturn around September 7 and 8, as shown on the sky chart above.

At the end of September 2019, it’ll be easier to view the planets Mercury and Venus than it was when this month began. The star Spica – brightest light in the constellation Virgo the Maiden – will be nearby. All of these objects will be easiest to see from Earth’s Southern Hemisphere this month. That’s because the ecliptic – or path of the sun, moon and planets – tilts steeply with respect to the sunset horizon in the autumn, and autumn begins in the Northern Hemisphere on September . Read more.

Mercury and Venus are both nominally evening planets all through September 2019, but both sit way too close to the glare of sunset to be visible at mid-northern latitudes for most of the month. From the Southern Hemisphere, or the northern tropics, you might catch the young moon with both Mercury and Venus near the month’s end, as depicted on the sky chart above.

Note that Venus – the brightest planet – is much brighter than Mercury.

By the way, at Mercury’s most recent inferior conjunction on July 21, 2019, Mercury swung to the south of the sun’s disk as seen from Earth. But when Mercury reaches its next inferior conjunction on November 11, 2019, the innermost planet will swing directly in front of the sun, to stage a transit of Mercury. Transits of Mercury happen more frequently than transits of Venus; they happen 13 or 14 times per century. The last transit of Mercury happened on May 9, 2016, and – after the one on this upcoming November 11 – the next Mercury transit won’t be until November 13, 2032.

You probably won’t see Mars again until late October, 2019. The waning crescent moon will point to Mars on October 23, 24 and 25. On October 26, look for the moon to swing close to Mars on the sky’s dome. Read more.

Where is Mars? Note that the above sky chart is for late October, not September! That’s because late October may feature your first decent chance to catch this world before sunrise. Mars swings on the far side of the sun at superior conjunction on September 2, 2019, to transition from the evening to morning sky. Hiding in the glare of sunrise, Mars probably won’t become visible in the morning sky until late October or November 2019.

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.

Skywatcher, by Predrag Agatonovic.

Bottom line: In September 2019, two planets – Jupiter and Saturn – are easy to see throughout the month. They both come out at nightfall and are out until late night. Mercury and Venus are pretty much lost in the afterglow of sunset, whereas Mars is hiding in the glare of sunrise. Click here for recommended almanacs; they can help you know when the planets rise and set in your sky.

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

Visit EarthSky’s Best Places to Stargaze, and recommend a place we can all enjoy.

Help EarthSky keep going! Donate now.

Post your planet photos at EarthSky Community Photos

from EarthSky https://ift.tt/1YD00CF

40 years ago today: Pioneer 11 swept past Saturn

This image from Pioneer 11 – taken when the spacecraft was 1,768,422 miles (2,846,000 km) from Saturn – shows Saturn and its largest moon Titan. The irregularities in ring silhouette and shadow are due to technical anomalies in the preliminary data, later corrected. Image via NASA.

On September 1, 1979 – 40 years ago today – NASA’s Pioneer 11 came within 13,000 miles (21,000 km) of Saturn, making it the first spacecraft ever to sweep closely past that world. The spacecraft found a new ring for Saturn – now called the “F” ring – and also two new moons, almost smacking into one of them as it soared past. It was an astounding achievement at the time, when spacecraft from Earth were just beginning to venture outward. More importantly, Pioneer 11 did what pioneers always do: it paved the way for those who came after it, including the two Voyager spacecraft, which launched in 1977 and visited Saturn in 1980 and ’81. Ultimately, Pioneer 11 helped lay the groundwork for the wonderful Cassini mission to Saturn, which orbited the planet from 2004 to 2017 and which provided unprecedented and spectacular views of Saturn and its rings and moons.

There were two Pioneer spacecraft. Pioneer 10 visited Jupiter, and Pioneer 11 was used to investigate Saturn’s rings and to learn if a trajectory through the rings was safe for the upcoming Voyager spacecraft.

Scientists said that Pioneer 11 also enabled them to get a sense of Saturn’s internal composition. It’s long been said that Saturn is not very dense and that – if you could find an ocean large enough to hold it – Saturn would float on water. Pioneer 11 showed Saturn likely has a relatively small core for an outer gas giant world – only 10 times Earth’s mass – and that the planet is mostly liquid hydrogen.

Pioneer 11 is still sailing away from Earth, even though its transmission was received on September 30, 1995. As far as scientists know, the spacecraft is still moving outward – in the general direction of the center of our Milky Way galaxy – that is, generally in the direction of our constellation Sagittarius.

Visit Cassini spacecraft image Hall of Fame

View larger. | As the years passed, and spacecraft imaging technology became more sophisticated, the images of this world vastly improved. Here’s a Cassini spacecraft image of Saturn showing the planet’s northern hemisphere in 2016, as that part of the planet neared its summer solstice in May 2017. Saturn’s year is nearly 30 Earth-years long, and during its long time there, Cassini observed winter and spring in Saturn’s northern hemisphere, and summer and fall in the southern hemisphere. Read more about this image.

Bottom line: On September 1, 1979, Pioneer 11 came closest to Saturn.

from EarthSky https://ift.tt/2UmKwbl

This image from Pioneer 11 – taken when the spacecraft was 1,768,422 miles (2,846,000 km) from Saturn – shows Saturn and its largest moon Titan. The irregularities in ring silhouette and shadow are due to technical anomalies in the preliminary data, later corrected. Image via NASA.

On September 1, 1979 – 40 years ago today – NASA’s Pioneer 11 came within 13,000 miles (21,000 km) of Saturn, making it the first spacecraft ever to sweep closely past that world. The spacecraft found a new ring for Saturn – now called the “F” ring – and also two new moons, almost smacking into one of them as it soared past. It was an astounding achievement at the time, when spacecraft from Earth were just beginning to venture outward. More importantly, Pioneer 11 did what pioneers always do: it paved the way for those who came after it, including the two Voyager spacecraft, which launched in 1977 and visited Saturn in 1980 and ’81. Ultimately, Pioneer 11 helped lay the groundwork for the wonderful Cassini mission to Saturn, which orbited the planet from 2004 to 2017 and which provided unprecedented and spectacular views of Saturn and its rings and moons.

There were two Pioneer spacecraft. Pioneer 10 visited Jupiter, and Pioneer 11 was used to investigate Saturn’s rings and to learn if a trajectory through the rings was safe for the upcoming Voyager spacecraft.

Scientists said that Pioneer 11 also enabled them to get a sense of Saturn’s internal composition. It’s long been said that Saturn is not very dense and that – if you could find an ocean large enough to hold it – Saturn would float on water. Pioneer 11 showed Saturn likely has a relatively small core for an outer gas giant world – only 10 times Earth’s mass – and that the planet is mostly liquid hydrogen.

Pioneer 11 is still sailing away from Earth, even though its transmission was received on September 30, 1995. As far as scientists know, the spacecraft is still moving outward – in the general direction of the center of our Milky Way galaxy – that is, generally in the direction of our constellation Sagittarius.

Visit Cassini spacecraft image Hall of Fame

View larger. | As the years passed, and spacecraft imaging technology became more sophisticated, the images of this world vastly improved. Here’s a Cassini spacecraft image of Saturn showing the planet’s northern hemisphere in 2016, as that part of the planet neared its summer solstice in May 2017. Saturn’s year is nearly 30 Earth-years long, and during its long time there, Cassini observed winter and spring in Saturn’s northern hemisphere, and summer and fall in the southern hemisphere. Read more about this image.

Bottom line: On September 1, 1979, Pioneer 11 came closest to Saturn.

from EarthSky https://ift.tt/2UmKwbl

Two Friday the 13ths in 2019

Image via les affaires.

We have two Friday the 13ths this year. Friday, September 13, 2019, presents the first one. Friday, December 13, 2019, gives us the second Friday the 13th. Unusual? Not particularly. Any calendar year has at least one Friday the 13th, and can have as many as three Friday the 13ths. Not that we at EarthSky suffer from friggatriskaidekaphobia – an irrational fear of Friday the 13th – but, gosh darn, the Friday the 13th in September happens exactly 13 weeks before 2019’s second Friday the 13th in December.

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 (February, March, November).

Read more: This year’s Harvest Moon will fall on Friday, September 13, 2019

After the Friday the 13th in December 2019, the following Friday the 13th will occur exactly 13 weeks after that: March 13, 2020.

Yikes, these few coincidences involving the number 13 are only the tip of the iceberg. We could cite more …

Keep reading to investigate the intriguing mathematics behind Friday the 13th and the calendar.

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.

Are all these Friday the 13ths a super coincidence? Super unlucky? Neither. They’re just a quirk of our calendar.

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.

Still, 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.

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

We have two Friday the 13ths in 2019 – in September and December – because 2019 is a common year (not a leap year) that started on a Tuesday. Whenever a common year of 365 days starts on a Tuesday, it’s inevitable that the months of September and December will start on a Sunday. And any month starting on a Sunday will have a Friday the 13th.

The last time a common year started on a Tuesday was six years ago, in the year 2013, and the next time will be 11 years from 2019, in 2030.

In addition, when any leap year of 366 days begins on a Monday, there are Friday the 13ths in September and December, as well. This September-December Friday the 13th leap year will take place five years from now, in 2024.

Some of you may wonder if there’s some formula that governs how the Friday the 13th drama repeats itself. The answer is yes! Keep in mind that a twofold September-December Friday the 13th year can only happen during a common year of 365 days, when January 1 falls on a Tuesday – or in a leap year of 366 days, when January 1 falls on a Monday. Let the intriguing number play begin …

The first twofold September-December Friday the 13th year in the 21st century (2001 to 2100) occurred in 2002, 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:

2002 + 11 = 2013

2002 + 17 = 2019

2002 + 28 = 2030

September 2019 calendar via TimeandDate.

How often do September-December Friday the 13ths happen? More often than you might imagine! We continue the cycle onward to find a grand total of 11 September-December Friday the 13th 365-day common years for the 21st century (2001 to 2100):

2002, 2013, 2019, 2030, 2041, 2047, 2058, 2069, 2075, 2086 and 2097

In the 21st century (2001 to 2100), the first September-December Friday the 13th leap year of 366 days occurs in 2024. This September-December Friday the 13th leap year recurs in cycles of 28 years:

2024 + 28 = 2052

2052 + 28 = 2080

So we find a total of three September-December Friday the 13th leap years in the 21st century(2001 to 2100): 2024, 2052 and 2080.

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, these twofold September-December Friday the 13th years recur in cycles of 400 years. For example, respective September-December Friday the 13th calendar years are exactly 400 years apart in the 21st and 25th centuries:

21st century (2001 to 2100):

2002, 2013, 2019, 2024 (leap year), 2030, 2041, 2047, 2052 (leap year), 2058, 2069, 2075, 2080 (leap year), 2086 and 2097

25th century (2401 to 2500):

2402, 2413, 2419, 2424 (leap year), 2430, 2441, 2447, 2452 (leap year), 2458, 2469, 2475, 2480 (leap year), 2486 and 2497

How about in other centuries? If you’re up for doing the computations:

22nd century (2101 to 2200): the first common year September-December Friday the 13th happens in 2109, and repeats in cycles of 6, 17 and 28 years. The first leap year September-December Friday the 13th happens in 2120 and recurs every 28 years.

23rd century (2201 to 2300): the first common September-December Friday the 13th year happens in 2205, and repeats every 6, 17 and 28 years. The first leap year September-December Friday the 13th happens in 2216 – but, by Gregorian calendar rules, the year 2300 is not a leap year.

24th century (2301 to 2400): the first common September-December Friday the 13th year happens in 2301, with the days and dates matching up again in periods of 6, 17 and 28 years. The first leap year September-December Friday the 13th happens in 2216.

As magical as all of this Friday the 13th calendar intrigue appears to be, it’s not supernatural. It’s entertaining number play, even if it may haunt our uncomprehending minds.

“… 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. Today – September 13, 2019 – presents the first Friday the 13th in 2019. Then, exactly 13 weeks after that, 2019’s second Friday the 13th will fall in December.

from EarthSky https://ift.tt/2PyeABK

Image via les affaires.

We have two Friday the 13ths this year. Friday, September 13, 2019, presents the first one. Friday, December 13, 2019, gives us the second Friday the 13th. Unusual? Not particularly. Any calendar year has at least one Friday the 13th, and can have as many as three Friday the 13ths. Not that we at EarthSky suffer from friggatriskaidekaphobia – an irrational fear of Friday the 13th – but, gosh darn, the Friday the 13th in September happens exactly 13 weeks before 2019’s second Friday the 13th in December.

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 (February, March, November).

Read more: This year’s Harvest Moon will fall on Friday, September 13, 2019

After the Friday the 13th in December 2019, the following Friday the 13th will occur exactly 13 weeks after that: March 13, 2020.

Yikes, these few coincidences involving the number 13 are only the tip of the iceberg. We could cite more …

Keep reading to investigate the intriguing mathematics behind Friday the 13th and the calendar.

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.

Are all these Friday the 13ths a super coincidence? Super unlucky? Neither. They’re just a quirk of our calendar.

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.

Still, 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.

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

We have two Friday the 13ths in 2019 – in September and December – because 2019 is a common year (not a leap year) that started on a Tuesday. Whenever a common year of 365 days starts on a Tuesday, it’s inevitable that the months of September and December will start on a Sunday. And any month starting on a Sunday will have a Friday the 13th.

The last time a common year started on a Tuesday was six years ago, in the year 2013, and the next time will be 11 years from 2019, in 2030.

In addition, when any leap year of 366 days begins on a Monday, there are Friday the 13ths in September and December, as well. This September-December Friday the 13th leap year will take place five years from now, in 2024.

Some of you may wonder if there’s some formula that governs how the Friday the 13th drama repeats itself. The answer is yes! Keep in mind that a twofold September-December Friday the 13th year can only happen during a common year of 365 days, when January 1 falls on a Tuesday – or in a leap year of 366 days, when January 1 falls on a Monday. Let the intriguing number play begin …

The first twofold September-December Friday the 13th year in the 21st century (2001 to 2100) occurred in 2002, 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:

2002 + 11 = 2013

2002 + 17 = 2019

2002 + 28 = 2030

September 2019 calendar via TimeandDate.

How often do September-December Friday the 13ths happen? More often than you might imagine! We continue the cycle onward to find a grand total of 11 September-December Friday the 13th 365-day common years for the 21st century (2001 to 2100):

2002, 2013, 2019, 2030, 2041, 2047, 2058, 2069, 2075, 2086 and 2097

In the 21st century (2001 to 2100), the first September-December Friday the 13th leap year of 366 days occurs in 2024. This September-December Friday the 13th leap year recurs in cycles of 28 years:

2024 + 28 = 2052

2052 + 28 = 2080

So we find a total of three September-December Friday the 13th leap years in the 21st century(2001 to 2100): 2024, 2052 and 2080.

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, these twofold September-December Friday the 13th years recur in cycles of 400 years. For example, respective September-December Friday the 13th calendar years are exactly 400 years apart in the 21st and 25th centuries:

21st century (2001 to 2100):

2002, 2013, 2019, 2024 (leap year), 2030, 2041, 2047, 2052 (leap year), 2058, 2069, 2075, 2080 (leap year), 2086 and 2097

25th century (2401 to 2500):

2402, 2413, 2419, 2424 (leap year), 2430, 2441, 2447, 2452 (leap year), 2458, 2469, 2475, 2480 (leap year), 2486 and 2497

How about in other centuries? If you’re up for doing the computations:

22nd century (2101 to 2200): the first common year September-December Friday the 13th happens in 2109, and repeats in cycles of 6, 17 and 28 years. The first leap year September-December Friday the 13th happens in 2120 and recurs every 28 years.

23rd century (2201 to 2300): the first common September-December Friday the 13th year happens in 2205, and repeats every 6, 17 and 28 years. The first leap year September-December Friday the 13th happens in 2216 – but, by Gregorian calendar rules, the year 2300 is not a leap year.

24th century (2301 to 2400): the first common September-December Friday the 13th year happens in 2301, with the days and dates matching up again in periods of 6, 17 and 28 years. The first leap year September-December Friday the 13th happens in 2216.

As magical as all of this Friday the 13th calendar intrigue appears to be, it’s not supernatural. It’s entertaining number play, even if it may haunt our uncomprehending minds.

“… 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. Today – September 13, 2019 – presents the first Friday the 13th in 2019. Then, exactly 13 weeks after that, 2019’s second Friday the 13th will fall in December.

from EarthSky https://ift.tt/2PyeABK