Asteroid Day 2017 is June 30

Image via Debbie Lewis

Image via Debbie Lewis

The third annual International Asteroid Day happens tomorrow, June 30, 2017. According to its organizers, Asteroid Day is a global awareness campaign to help people learn about asteroids and what we can do to protect our planet from asteroid impacts.

Asteroid Day is held on the anniversary of the largest asteroid impact in Earth’s recent history – an event that took place in Siberia on June 30, 1908, known as the Tunguska explosion. A small asteroid apparently exploded over Tunguska, Siberia. It released the equivalent of 100 tons of TNT, devastating an area of about 800 square miles, the size of a major metropolitan city.

NASA will mark Asteroid Day 2017 at noon EDT Friday, June 30, with a program airing on NASA TV on how researchers find, track and characterize NEOs – asteroids and comets that come within the vicinity of Earth’s orbit and could pose an impact hazard to Earth – and how NASA is working to get our nation prepared to respond to a potential impact threat. Watch here.

NASA Planetary Defense Officer Lindley Johnson said in a statement:

At NASA, every day is an asteroid day, but we value the international collaboration for a designated day to call attention to the importance of detecting and tracking hazardous asteroids.

The NASA broadcast will be part of a 24-hour Asteroid Day program from Broadcasting Center Europe, beginning at 9 p.m. ETD June 29 (1 a.m. June 30 UTC translate to your time zone) and streaming online here.

Asteroid Day Live

An object entered the atmosphere over the Urals early in the morning of 15 February 2013. The fireball exploded above Chelyabinsk city, and the resulting overpressure caused damage to buildings and injuries to hundreds of people. This photo was taken by Alex Alishevskikh from about a minute after noticing the blast. Photo credit: Alex Alishevskikh/Flickr

An object entered the atmosphere over the Urals early in the morning of February 15, 2013. The fireball exploded above Chelyabinsk city, resulting in damage to buildings and injuries to some 1,500 people. This photo was taken by Alex Alishevskikh from about a minute after noticing the blast. Photo via Alex Alishevskikh/Flickr

Here’s the premise of Asteroid Day, in the words of co-founder Dr. Brian May, astrophysicist, guitarist and songwriter for the band Queen:

Our goal is to dedicate one day each year to learn about asteroids, the origins of our universe, and to support the resources necessary to see, track and deflect dangerous asteroids from Earth’s orbital path. Asteroids are a natural disaster we know how to prevent.

Brian May

Astrophysicist and Queen guitarist Brian May is a co-founder of Asteroid Day.

For asteroid news and updates, follow AsteroidWatch on Twitter:

Bottom line: International Asteroid Day 2017 happens on Friday, June 30.

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Image via Debbie Lewis

Image via Debbie Lewis

The third annual International Asteroid Day happens tomorrow, June 30, 2017. According to its organizers, Asteroid Day is a global awareness campaign to help people learn about asteroids and what we can do to protect our planet from asteroid impacts.

Asteroid Day is held on the anniversary of the largest asteroid impact in Earth’s recent history – an event that took place in Siberia on June 30, 1908, known as the Tunguska explosion. A small asteroid apparently exploded over Tunguska, Siberia. It released the equivalent of 100 tons of TNT, devastating an area of about 800 square miles, the size of a major metropolitan city.

NASA will mark Asteroid Day 2017 at noon EDT Friday, June 30, with a program airing on NASA TV on how researchers find, track and characterize NEOs – asteroids and comets that come within the vicinity of Earth’s orbit and could pose an impact hazard to Earth – and how NASA is working to get our nation prepared to respond to a potential impact threat. Watch here.

NASA Planetary Defense Officer Lindley Johnson said in a statement:

At NASA, every day is an asteroid day, but we value the international collaboration for a designated day to call attention to the importance of detecting and tracking hazardous asteroids.

The NASA broadcast will be part of a 24-hour Asteroid Day program from Broadcasting Center Europe, beginning at 9 p.m. ETD June 29 (1 a.m. June 30 UTC translate to your time zone) and streaming online here.

Asteroid Day Live

An object entered the atmosphere over the Urals early in the morning of 15 February 2013. The fireball exploded above Chelyabinsk city, and the resulting overpressure caused damage to buildings and injuries to hundreds of people. This photo was taken by Alex Alishevskikh from about a minute after noticing the blast. Photo credit: Alex Alishevskikh/Flickr

An object entered the atmosphere over the Urals early in the morning of February 15, 2013. The fireball exploded above Chelyabinsk city, resulting in damage to buildings and injuries to some 1,500 people. This photo was taken by Alex Alishevskikh from about a minute after noticing the blast. Photo via Alex Alishevskikh/Flickr

Here’s the premise of Asteroid Day, in the words of co-founder Dr. Brian May, astrophysicist, guitarist and songwriter for the band Queen:

Our goal is to dedicate one day each year to learn about asteroids, the origins of our universe, and to support the resources necessary to see, track and deflect dangerous asteroids from Earth’s orbital path. Asteroids are a natural disaster we know how to prevent.

Brian May

Astrophysicist and Queen guitarist Brian May is a co-founder of Asteroid Day.

For asteroid news and updates, follow AsteroidWatch on Twitter:

Bottom line: International Asteroid Day 2017 happens on Friday, June 30.

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



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Star of the week:Antares is Heart of the Scorpion

Red Antares, via Fred Espenak at AstroPixels. Used with permission.

Red Antares, via Fred Espenak at AstroPixels. Used with permission.

Bright reddish Antares – also known as Alpha Scorpii – is easy to spot on a summer night. It is the brightest star – and distinctly reddish in color – in the fishhook-shaped pattern of stars known as the constellation Scorpius the Scorpion. Follow the links below to learn more about this wonderful star.

How to see Antares

Antares science

Antares in history and myth

From northerly latitudes, look in your southern sky at nightfall for the planets Mars and Saturn, plus the star Antares, the brightest star in the constellation Scorpius.

In 2016, the planets Mars and Saturn make a noticeable triangle with the star Antares, as seen from around the globe.

Scorpius is one of the few constellations that looks like its namesake. The bright red star Antares marks the Scorpion's Heart. Notice also the two stars at the tip of the Scorpion's Tail. They are known as The Stinger.

Scorpius is one of the few constellations that looks like its namesake. The bright red star Antares marks the Scorpion’s Heart. Notice also the two stars at the tip of the Scorpion’s Tail. They are known as The Stinger.

How to see Antares. If you look southward in early evening from late spring to early fall, you’re likely to notice the fishhook pattern of Scorpius the Scorpion, with ruby Antares at its heart. If you think you’ve found Antares, aim binoculars in its direction. You should notice its reddish color. And you should see a little star cluster – known as M4 – just to the right of this star. (See images above)

Antares is the 16th brightest star in the sky, and it is located in the southern half of Earth’s sky. So your chance of seeing this star on any given night increases as you go farther southward on Earth’s globe. If you traveled to the southern hemisphere – from about 67 degrees south latitude – you’d find that Antares is circumpolar, meaning that it never sets and is visible every night of the year from Earth’s southernmost regions.

We in the northern hemisphere know Antares better than several other southern stars that are brighter. That’s because Antares is visible from throughout most of the northern hemisphere, short of the Arctic. Well, not quite the Arctic, but anywhere south of 63 degrees north latitude can – at one time or another – see Antares. (Helsinki yes, Fairbanks, no)

The midnight culmination of Antares is on or near June 1. That is when Antares is highest in the sky at midnight (midway between sunset and sunrise). It is highest in the sky at about dawn in early March and at about sunset in early September.

If Antares replaced the sun in our solar system, its orbit would extend beyond the orbit of the fourth planet, Mars. Here, Antares is shown in contrast to another star, Arcturus, and our sun. Image via Wikimedia Commons.

If Antares replaced the sun in our solar system, its orbit would extend beyond the orbit of the fourth planet, Mars. Here, Antares is shown in contrast to another star, Arcturus, and our sun. Image via Wikimedia Commons.

Antares science. Antares is truly an enormous star, with a radius in excess of 3 Astronomical Units (AU). One AU is the Earth’s average distance from the sun. If by some bit of magic Antares was suddenly substituted for our sun, the surface of the star would extend well past the orbit of Mars!

Antares is classified as an M1 supergiant star. The M1 designation says that Antares is reddish in color and cooler than many other stars. Its surface temperature of 3500 kelvins (about 5800 degrees F.) is in contrast to about 10,000 degrees F. for our sun.

Even though Antares’ surface temperature is relatively low, Antares’ tremendous surface area – the surface from which light can escape – makes this star very bright. In fact, Antares approaches 11,000 times the brilliance of our puny sun, a G2 star.

But that is just in visible light. When all wavelengths of electromagnetic radiation is considered, Antares pumps out more than 60,000 times the energy of our sun!

Red Antares is similar to but somewhat larger than another famous red star, Betelgeuse in the constellation Orion. Yet Betelgeuse appears slightly brighter than Antares in our sky. Hipparcos satellite data places Antares at about 604 light-years away, in contrast to Betelgeuse’s distance of 428 light-years, explaining why the larger star appears fainter from Earth.

Like all M-type giants and supergiants, Antares is close to the end of its lifetime. Someday soon (astronomically speaking), it will effectively run out of fuel and collapse. The resulting infall of its enormous mass – some 15-18 times the mass of our sun – will cause an immense supernova explosion, ultimately leaving a tiny neutron star or possibly a black hole. This explosion, which could be tomorrow or millions of years from now, will be spectacular as seen from Earth, but we are far enough away that there likely is no danger to our planet.

Scorpius, via Constellation of Words

Scorpius, via Constellation of Words

Antares in history and myth. Both the Arabic and Latin names for the star Antares mean “heart of the Scorpion.” If you see this constellation in the sky, you’ll find that Antares does indeed seem to reside at the Scorpion’s heart.

Antares is Greek for “like Mars” or “rivaling Mars.” Antares is sometimes said to be the “anti-Mars.” All of this rivalry (or equivalency … for what is rivalry, after all?) stems from the colors of Mars and Antares. Both are red in color, and, for a few months every couple of years Mars is much brighter than Antares. Most of the time, though, Mars is near the same brightness or much fainter than Antares. Every couple of years, Mars passes near Antares, which was perhaps seen as taunting the star, as Mars moves rapidly through the heavens and Antares, like all stars, seems fixed to the starry firmament.

As is typical, more mythology attends the full constellation of Scorpius than the star Antares. Perhaps the most well known story of Scorpius is that the Earth goddess, Gaia, sent him to sting arrogant Orion, who had claimed his intent to kill all animals on the planet. Scorpius killed Orion, and both were placed in the sky, although in opposite sides of the heavens, positioned as if to show the Scorpion chasing the Mighty Hunter.

Interestingly, Betelgeuse in the constellation Orion is similar in appearance to Antares, although brighter. Betelgeuse is not as associated with Mars as is Antares. Although the planet passes in the vicinity of Betelgeuse every couple of years, it never gets as close as it does to Antares.

In Polynesia, Scorpius is often seen as a fishhook, with some stories describing it as the magic fishhook used by the demigod Maui to pull up land from the ocean floor that became the Hawaiian islands. According to the University of Hawaii’s Institute for Astronomy website, the Hawaiian name for Antares, Lehua-kona, seems to have little to do with the constellation. It means “southern lehua blossom.”

Antares’ position is RA:16h 29m 24s, dec: -26° 25′ 55″.

Image via Dick Loke

The red star Antares, lower left, near the prominent star cluster M4, right. Image via Dick Locke

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Shaula and Lesath: Scorpion’s Stinger stars



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Red Antares, via Fred Espenak at AstroPixels. Used with permission.

Red Antares, via Fred Espenak at AstroPixels. Used with permission.

Bright reddish Antares – also known as Alpha Scorpii – is easy to spot on a summer night. It is the brightest star – and distinctly reddish in color – in the fishhook-shaped pattern of stars known as the constellation Scorpius the Scorpion. Follow the links below to learn more about this wonderful star.

How to see Antares

Antares science

Antares in history and myth

From northerly latitudes, look in your southern sky at nightfall for the planets Mars and Saturn, plus the star Antares, the brightest star in the constellation Scorpius.

In 2016, the planets Mars and Saturn make a noticeable triangle with the star Antares, as seen from around the globe.

Scorpius is one of the few constellations that looks like its namesake. The bright red star Antares marks the Scorpion's Heart. Notice also the two stars at the tip of the Scorpion's Tail. They are known as The Stinger.

Scorpius is one of the few constellations that looks like its namesake. The bright red star Antares marks the Scorpion’s Heart. Notice also the two stars at the tip of the Scorpion’s Tail. They are known as The Stinger.

How to see Antares. If you look southward in early evening from late spring to early fall, you’re likely to notice the fishhook pattern of Scorpius the Scorpion, with ruby Antares at its heart. If you think you’ve found Antares, aim binoculars in its direction. You should notice its reddish color. And you should see a little star cluster – known as M4 – just to the right of this star. (See images above)

Antares is the 16th brightest star in the sky, and it is located in the southern half of Earth’s sky. So your chance of seeing this star on any given night increases as you go farther southward on Earth’s globe. If you traveled to the southern hemisphere – from about 67 degrees south latitude – you’d find that Antares is circumpolar, meaning that it never sets and is visible every night of the year from Earth’s southernmost regions.

We in the northern hemisphere know Antares better than several other southern stars that are brighter. That’s because Antares is visible from throughout most of the northern hemisphere, short of the Arctic. Well, not quite the Arctic, but anywhere south of 63 degrees north latitude can – at one time or another – see Antares. (Helsinki yes, Fairbanks, no)

The midnight culmination of Antares is on or near June 1. That is when Antares is highest in the sky at midnight (midway between sunset and sunrise). It is highest in the sky at about dawn in early March and at about sunset in early September.

If Antares replaced the sun in our solar system, its orbit would extend beyond the orbit of the fourth planet, Mars. Here, Antares is shown in contrast to another star, Arcturus, and our sun. Image via Wikimedia Commons.

If Antares replaced the sun in our solar system, its orbit would extend beyond the orbit of the fourth planet, Mars. Here, Antares is shown in contrast to another star, Arcturus, and our sun. Image via Wikimedia Commons.

Antares science. Antares is truly an enormous star, with a radius in excess of 3 Astronomical Units (AU). One AU is the Earth’s average distance from the sun. If by some bit of magic Antares was suddenly substituted for our sun, the surface of the star would extend well past the orbit of Mars!

Antares is classified as an M1 supergiant star. The M1 designation says that Antares is reddish in color and cooler than many other stars. Its surface temperature of 3500 kelvins (about 5800 degrees F.) is in contrast to about 10,000 degrees F. for our sun.

Even though Antares’ surface temperature is relatively low, Antares’ tremendous surface area – the surface from which light can escape – makes this star very bright. In fact, Antares approaches 11,000 times the brilliance of our puny sun, a G2 star.

But that is just in visible light. When all wavelengths of electromagnetic radiation is considered, Antares pumps out more than 60,000 times the energy of our sun!

Red Antares is similar to but somewhat larger than another famous red star, Betelgeuse in the constellation Orion. Yet Betelgeuse appears slightly brighter than Antares in our sky. Hipparcos satellite data places Antares at about 604 light-years away, in contrast to Betelgeuse’s distance of 428 light-years, explaining why the larger star appears fainter from Earth.

Like all M-type giants and supergiants, Antares is close to the end of its lifetime. Someday soon (astronomically speaking), it will effectively run out of fuel and collapse. The resulting infall of its enormous mass – some 15-18 times the mass of our sun – will cause an immense supernova explosion, ultimately leaving a tiny neutron star or possibly a black hole. This explosion, which could be tomorrow or millions of years from now, will be spectacular as seen from Earth, but we are far enough away that there likely is no danger to our planet.

Scorpius, via Constellation of Words

Scorpius, via Constellation of Words

Antares in history and myth. Both the Arabic and Latin names for the star Antares mean “heart of the Scorpion.” If you see this constellation in the sky, you’ll find that Antares does indeed seem to reside at the Scorpion’s heart.

Antares is Greek for “like Mars” or “rivaling Mars.” Antares is sometimes said to be the “anti-Mars.” All of this rivalry (or equivalency … for what is rivalry, after all?) stems from the colors of Mars and Antares. Both are red in color, and, for a few months every couple of years Mars is much brighter than Antares. Most of the time, though, Mars is near the same brightness or much fainter than Antares. Every couple of years, Mars passes near Antares, which was perhaps seen as taunting the star, as Mars moves rapidly through the heavens and Antares, like all stars, seems fixed to the starry firmament.

As is typical, more mythology attends the full constellation of Scorpius than the star Antares. Perhaps the most well known story of Scorpius is that the Earth goddess, Gaia, sent him to sting arrogant Orion, who had claimed his intent to kill all animals on the planet. Scorpius killed Orion, and both were placed in the sky, although in opposite sides of the heavens, positioned as if to show the Scorpion chasing the Mighty Hunter.

Interestingly, Betelgeuse in the constellation Orion is similar in appearance to Antares, although brighter. Betelgeuse is not as associated with Mars as is Antares. Although the planet passes in the vicinity of Betelgeuse every couple of years, it never gets as close as it does to Antares.

In Polynesia, Scorpius is often seen as a fishhook, with some stories describing it as the magic fishhook used by the demigod Maui to pull up land from the ocean floor that became the Hawaiian islands. According to the University of Hawaii’s Institute for Astronomy website, the Hawaiian name for Antares, Lehua-kona, seems to have little to do with the constellation. It means “southern lehua blossom.”

Antares’ position is RA:16h 29m 24s, dec: -26° 25′ 55″.

Image via Dick Loke

The red star Antares, lower left, near the prominent star cluster M4, right. Image via Dick Locke

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Shaula and Lesath: Scorpion’s Stinger stars



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Moon approaching Jupiter on June 29

Tonight – June 29, 2017 – you can’t miss the king planet Jupiter, given a clear sky! As soon as dusk or darkness falls, look first for the rather wide waxing crescent moon. That “star” in the moon’s vicinity tonight is actually Jupiter, the brightest starlike object to adorn the evening sky. The moon is approaching Jupiter as we speak, and will be noticeably closer to Jupiter as darkness falls tomorrow, on June 30.

Do you have binoculars? You can search for the Virgo star Zavijava (Beta Virginis) in the same binocular field with the moon. Although this faint star is easily visible to the unaided eye on a clear, dark night, it might be hard to see in the glare of the June 29 moon. The sky chart below is for mid-northern North American latitudes. On this same date at mid-northern latitudes in Europe and Asia, tonight’s moon will appear farther west (right) of Jupiter and Zavijava than it does in North America.

This chart of the moon and the Virgo star Zavijava (Beta Virginis) is for North America. On this same date in Europe, the moon will be approximately 3o (6 moon-diameters ) west or right of Zavijava. In Asia, the moon will be about 6o (12 moon-diameters) farther west than it is in North America.

As evening deepens, watch for the moon, Jupiter and Zavijava to move westward across the sky. At mid-northern latitudes, all three will set by around local midnight (1 a.m. Daylight Saving Time) tonight. Click here for an almanac telling you when the moon and Jupiter set in your sky.

The star Zavijava (Beta Virginis) almost aligns with the September equinox point. Sky chart via the International Astronomical Union (IAU) and Sky & Telescope.

The star Zavijava sits almost squarely on the ecliptic – the sun’s annual pathway in front of the constellations of the zodiac. But that’s not all. This star nearly marks the September equinox point, or where the sun lodges in the constellation Virgo on the day of the September equinox, which comes this year on September 22, 2017.

Purportedly, this star also played a pivotal role in helping to confirm Einstein’s general relativity theory during the total solar eclipse of September 21, 1922.

Earth’s spin causes the moon and Jupiter to go westward throughout the night. Meanwhile, due to its own motion in orbit, the moon travels eastward relative to the backdrop stars and planets of the zodiac. Tonight – June 29, 2017 – the moon will move eastward, toward Jupiter, at the rate of about ½ degree (the moon’s own angular diameter) per hour. That’s why everyone around the world will see the moon closer to Jupiter on the sky’s dome tomorrow, as darkness falls on June 30.

Bottom line: Tonight – June 29, 2017 – you can’t miss the moon and king planet Jupiter, given a clear sky!



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Tonight – June 29, 2017 – you can’t miss the king planet Jupiter, given a clear sky! As soon as dusk or darkness falls, look first for the rather wide waxing crescent moon. That “star” in the moon’s vicinity tonight is actually Jupiter, the brightest starlike object to adorn the evening sky. The moon is approaching Jupiter as we speak, and will be noticeably closer to Jupiter as darkness falls tomorrow, on June 30.

Do you have binoculars? You can search for the Virgo star Zavijava (Beta Virginis) in the same binocular field with the moon. Although this faint star is easily visible to the unaided eye on a clear, dark night, it might be hard to see in the glare of the June 29 moon. The sky chart below is for mid-northern North American latitudes. On this same date at mid-northern latitudes in Europe and Asia, tonight’s moon will appear farther west (right) of Jupiter and Zavijava than it does in North America.

This chart of the moon and the Virgo star Zavijava (Beta Virginis) is for North America. On this same date in Europe, the moon will be approximately 3o (6 moon-diameters ) west or right of Zavijava. In Asia, the moon will be about 6o (12 moon-diameters) farther west than it is in North America.

As evening deepens, watch for the moon, Jupiter and Zavijava to move westward across the sky. At mid-northern latitudes, all three will set by around local midnight (1 a.m. Daylight Saving Time) tonight. Click here for an almanac telling you when the moon and Jupiter set in your sky.

The star Zavijava (Beta Virginis) almost aligns with the September equinox point. Sky chart via the International Astronomical Union (IAU) and Sky & Telescope.

The star Zavijava sits almost squarely on the ecliptic – the sun’s annual pathway in front of the constellations of the zodiac. But that’s not all. This star nearly marks the September equinox point, or where the sun lodges in the constellation Virgo on the day of the September equinox, which comes this year on September 22, 2017.

Purportedly, this star also played a pivotal role in helping to confirm Einstein’s general relativity theory during the total solar eclipse of September 21, 1922.

Earth’s spin causes the moon and Jupiter to go westward throughout the night. Meanwhile, due to its own motion in orbit, the moon travels eastward relative to the backdrop stars and planets of the zodiac. Tonight – June 29, 2017 – the moon will move eastward, toward Jupiter, at the rate of about ½ degree (the moon’s own angular diameter) per hour. That’s why everyone around the world will see the moon closer to Jupiter on the sky’s dome tomorrow, as darkness falls on June 30.

Bottom line: Tonight – June 29, 2017 – you can’t miss the moon and king planet Jupiter, given a clear sky!



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Rainbow reflected at sunset

Rainbow reflected at sunset, via Fotograf Göran Strand. He captured this image in Vansbro, Sweden, over a river known as the Västerdalälven.

Göran Strand of Östersund, Sweden wrote:

The height of a rainbow depends on the height of the sun. When the sun is high in the sky we get a low rainbow and when the sun is low in the sky we get a higher rainbow.

In this picture taken by sunset, when the sun is at its lowest, the rainbow is the highest. With the reflection in the water you see that there is a perfect circle, this can only happen at sunset. If the sun was higher in the sky, we would have seen the rainbow and the reflection had the shape of an ellipse.

Outside the primary rainbow, it’s possible to suspect the secondary bow. It was a little more visible during shorter periods, but then the water wasn’t as cool.

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Rainbow reflected at sunset, via Fotograf Göran Strand. He captured this image in Vansbro, Sweden, over a river known as the Västerdalälven.

Göran Strand of Östersund, Sweden wrote:

The height of a rainbow depends on the height of the sun. When the sun is high in the sky we get a low rainbow and when the sun is low in the sky we get a higher rainbow.

In this picture taken by sunset, when the sun is at its lowest, the rainbow is the highest. With the reflection in the water you see that there is a perfect circle, this can only happen at sunset. If the sun was higher in the sky, we would have seen the rainbow and the reflection had the shape of an ellipse.

Outside the primary rainbow, it’s possible to suspect the secondary bow. It was a little more visible during shorter periods, but then the water wasn’t as cool.

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Be Cool this Summer with Hot Ice Cream

A new kitchen chemistry project at Science Buddies guides students in an exploration of a fun dessert that melts as it cools.

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A new kitchen chemistry project at Science Buddies guides students in an exploration of a fun dessert that melts as it cools.

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An upside down rainbow?

Photo taken May 13, 2017 by Tony Bowman in Surrey, England.

People who look up a lot may occasionally see the rainbow-like arcs depicted in the photos on this page. They’re called circumzenithal arcs, and they’re not really rainbows. Instead, they’re caused by ice crystals in the upper atmosphere. These arcs are related to the frequently seen halos around the sun or moon. Les Cowley of the great website Atmospheric Optics says of these graceful and colorful arcs:

The circumzenithal arc, CZA, is the most beautiful of all the halos. The first sighting is always a surprise, an ethereal rainbow fled from its watery origins and wrapped improbably about the zenith. It is often described as an “upside down rainbow” by first timers. Someone also charmingly likened it to “a grin in the sky”.

Look straight up near to the zenith when the sun if fairly low and especially if sundogs are visible. The centre of the bow always sunwards and red is on the outside.

Les says that the most ideal time to see a circumzenithal arc is when the sun is at a height of 22 degrees in the sky. Look here to see Les Cowley’s illustration of the various kinds of halo phenomena, related to circumzenithal arcs. And enjoy the photos below, contributed by members of the EarthSky community. Thanks to all who contributed!

Patricia Chambers caught this circumzenithal arc from Potomac, Maryland on August 5, 2016. She wrote:

Patricia Chambers caught this circumzenithal arc from Potomac, Maryland on August 5, 2016. She wrote: “It had rained not too long before I took the pic. I went out in my deck and saw an unbelievable sight – an upside down rainbow! I was truly mesmerized … Enjoy!”


Circumzenithal arc captured September 16, 2015 in Lancashire, UK by Amanda Cross.

Dan Szulewski captured a circumzenithal arc from Hermiston, Oregon on June 22, 2014.

Dan Szulewski captured a circumzenithal arc from Hermiston, Oregon on June 22, 2014.

Dorothy caught this circumzenithal arc on January 9, 2014.

Dorothy caught this circumzenithal arc on January 9, 2014.

Julie Gurnhill caught this one on February 27, 2013.

Julie Gurnhill caught this one on February 27, 2013.

John Gravell captured this circumzenithal arc from Boston on October 17, 2012.

John Gravell captured this circumzenithal arc from Boston on October 17, 2012.

Duke Marsh caught this circumzenithal arc on October 3, 2012 from New Albany, Indiana. Thanks, Duke.

Duke Marsh caught this circumzenithal arc on October 3, 2012 from New Albany, Indiana. Thanks, Duke.

Rene Pennings captured this circumzenithal arc on May 21, 2012.

Rene Pennings captured this circumzenithal arc on May 21, 2012.

A lovely circumzenithal arc amidst high clouds by Dudley Williams on December 18, 2011.

A lovely circumzenithal arc amidst high clouds by Dudley Williams on December 18, 2011.

Here's that same circumzenithal arc from Andrew R. Brown again, minus the jet!

Andrew R. Brown caught a circumzenithal arc in Ashford Kent in the UK, on November 19, 2010.

Bottom line: When you see an upside-down rainbow in the sky, you are likely seeing a circumzenithal arc. It’s related the halos often seen around the sun or moon, caused by ice crystal in the upper atmosphere.



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Photo taken May 13, 2017 by Tony Bowman in Surrey, England.

People who look up a lot may occasionally see the rainbow-like arcs depicted in the photos on this page. They’re called circumzenithal arcs, and they’re not really rainbows. Instead, they’re caused by ice crystals in the upper atmosphere. These arcs are related to the frequently seen halos around the sun or moon. Les Cowley of the great website Atmospheric Optics says of these graceful and colorful arcs:

The circumzenithal arc, CZA, is the most beautiful of all the halos. The first sighting is always a surprise, an ethereal rainbow fled from its watery origins and wrapped improbably about the zenith. It is often described as an “upside down rainbow” by first timers. Someone also charmingly likened it to “a grin in the sky”.

Look straight up near to the zenith when the sun if fairly low and especially if sundogs are visible. The centre of the bow always sunwards and red is on the outside.

Les says that the most ideal time to see a circumzenithal arc is when the sun is at a height of 22 degrees in the sky. Look here to see Les Cowley’s illustration of the various kinds of halo phenomena, related to circumzenithal arcs. And enjoy the photos below, contributed by members of the EarthSky community. Thanks to all who contributed!

Patricia Chambers caught this circumzenithal arc from Potomac, Maryland on August 5, 2016. She wrote:

Patricia Chambers caught this circumzenithal arc from Potomac, Maryland on August 5, 2016. She wrote: “It had rained not too long before I took the pic. I went out in my deck and saw an unbelievable sight – an upside down rainbow! I was truly mesmerized … Enjoy!”


Circumzenithal arc captured September 16, 2015 in Lancashire, UK by Amanda Cross.

Dan Szulewski captured a circumzenithal arc from Hermiston, Oregon on June 22, 2014.

Dan Szulewski captured a circumzenithal arc from Hermiston, Oregon on June 22, 2014.

Dorothy caught this circumzenithal arc on January 9, 2014.

Dorothy caught this circumzenithal arc on January 9, 2014.

Julie Gurnhill caught this one on February 27, 2013.

Julie Gurnhill caught this one on February 27, 2013.

John Gravell captured this circumzenithal arc from Boston on October 17, 2012.

John Gravell captured this circumzenithal arc from Boston on October 17, 2012.

Duke Marsh caught this circumzenithal arc on October 3, 2012 from New Albany, Indiana. Thanks, Duke.

Duke Marsh caught this circumzenithal arc on October 3, 2012 from New Albany, Indiana. Thanks, Duke.

Rene Pennings captured this circumzenithal arc on May 21, 2012.

Rene Pennings captured this circumzenithal arc on May 21, 2012.

A lovely circumzenithal arc amidst high clouds by Dudley Williams on December 18, 2011.

A lovely circumzenithal arc amidst high clouds by Dudley Williams on December 18, 2011.

Here's that same circumzenithal arc from Andrew R. Brown again, minus the jet!

Andrew R. Brown caught a circumzenithal arc in Ashford Kent in the UK, on November 19, 2010.

Bottom line: When you see an upside-down rainbow in the sky, you are likely seeing a circumzenithal arc. It’s related the halos often seen around the sun or moon, caused by ice crystal in the upper atmosphere.



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Solar eclipse safe viewing tips

It is never safe to look directly at the sun’s rays – even if the sun is partly obscured. When watching a partial eclipse you must wear eclipse glasses at all times if you want to face the sun, or use an alternate indirect method. This also applies during a total eclipse up until the time when the sun is completely and totally blocked.

Total eclipse of sun: August 21, 2017

Purchase solar eclipse viewing glasses here

Bottom line: Safety tips for watching the August 21, 2017 total solar eclipse.

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It is never safe to look directly at the sun’s rays – even if the sun is partly obscured. When watching a partial eclipse you must wear eclipse glasses at all times if you want to face the sun, or use an alternate indirect method. This also applies during a total eclipse up until the time when the sun is completely and totally blocked.

Total eclipse of sun: August 21, 2017

Purchase solar eclipse viewing glasses here

Bottom line: Safety tips for watching the August 21, 2017 total solar eclipse.

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



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