Editors of EarthSky | EarthSky

Orion the Hunter and the Milky Way on December evenings

Editors of EarthSky — Sun, 17 Dec 2023 11:01:00 +0000

On December and January evenings, you’ll find a faint band – what we in the Northern Hemisphere call the “winter” Milky Way – stretching up from the horizon and running through the constellation Orion the Hunter. Notice Orion’s 3 Belt stars. They’re easy to spot in the sky. But you’ll need a dark sky to see the Milky Way.

Orion the Hunter on December evenings

Tonight, or any December evening, find the famous constellation Orion the Hunter. It’s bright and can be seen from inside smaller cities. And the three stars that make up Orion’s Belt – in a short, straight row at the Hunter’s midsection – are very noticeable. If you have a dark sky, you can see something else: the starry band of the Milky Way – the edgewise view of our home galaxy – running behind Orion.

As seen from the Northern Hemisphere, after Orion rises, the three stars of Orion’s Belt jut more or less straight up from the horizon. Look on either side of the Belt stars for two very bright stars. One is the reddish star Betelgeuse. The other is bright, blue-white Rigel.

Throughout December, the constellation Orion is well up by mid-evening (by that we mean by midway between your local sunset and your local midnight). Like all of the starry sky, as Earth moves around the sun, Orion rises earlier each evening. So, by late December, Orion will be seen at nightfall or early evening. That’s true for both the Southern and Northern Hemispheres.

Orion is a summer constellation for the Southern Hemisphere.

But we in the Northern Hemisphere associate Orion with winter nights. That’s because this constellation is up throughout our long December and January nights.

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Orion the Hunter, captured by astrophotographer Alan Dyer. Rigel appears in the lower right of the constellation. Contrast its bluish-white light with that of reddish Betelgeuse in the upper left. Image via Alan Dyer/ AmazingSKY.com. Used with permission.

Use Orion to find the Milky Way

Because so many people are familiar with Orion, this constellation is a great jumping off spot for finding the starry pathway of the Milky Way. You’ll need a dark sky to see the hazy arc of stars running behind the bright red star Betelgeuse.

Looking at the Milky Way in our sky is looking edgewise into the disk of our galaxy. We see the galaxy as the combined glow of billions of stars. You might know that – in the month of August – the Milky Way appears broad and bright during the evening hours. At that time of year, in the evening, all of us on Earth are gazing toward the star-rich center of the galaxy.

Now Earth has traveled in its orbit around the sun, and our evening sky is pointing out in a different direction. If you see the Milky Way behind the constellation Orion this month, you might think it’s very faint in contrast to the August Milky Way. It is fainter, because now we’re looking toward the galaxy’s outer edge. There are fewer stars between us and intergalactic space.

Orion is easy to spot

At least part of Orion is visible from anywhere on the globe. It’s visible in the evening sky for Northern Hemisphere observers from late autumn through early spring. On the other hand, it’s visible in the summer evening sky from the Southern Hemisphere.

Here’s Orion higher in the sky, later at night in December, with the faint constellation Monoceros the Unicorn, plus the bright stars Sirius and Procyon. If you have a dark sky, you’ll find the faint winter Milky Way running behind them all.

View at EarthSky Community Photos. | Sergei Timofeevski shared this image from November 13, 2023. Sergei wrote: “The constellation Orion the Hunter and the star Sirius rising just above the eastern horizon in the Anza-Borrego Desert State Park, California.” Thank you, Sergei! See the orangish star marking one of Orion’s shoulders? That’s the star Betelgeuse.

Bottom line: You can find one of the most famous constellations – Orion the Hunter – plus see the Milky Way tonight.

Easily locate stars and constellations during any day and time with EarthSky’s planisphere

The post Orion the Hunter and the Milky Way on December evenings first appeared on EarthSky.

The Wright brothers succeeded 120 years ago

Editors of EarthSky — Sun, 17 Dec 2023 11:00:59 +0000

One of the world’s most famous photographs serves to commemorate the Wright brothers’ airplane on its 1st powered flight on December 17, 1903. Image via John T. Daniels/ Wikipedia (public domain).

First successful flight on December 17, 1903

On this date, 120 years ago, two Ohio brothers – Wilbur and Orville Wright – made the first bonafide, manned, controlled, heavier-than-air flight. It was the first airplane, and it took off at 10:35 a.m. with Orville Wright on board as pilot. He flew their vehicle, called the Flyer, for 12 seconds over 40 yards (about 37 meters) of sandy ground just outside Kitty Hawk, North Carolina. The Wright brothers succeeded where numerous other talented visionaries failed.

Two years later, the Wrights wrote in a patent application that their airplane design:

… provide[s] means for guiding the machine both vertically and horizontally … combining lightness, strength, convenience of construction, and certain other advantages.

The Wright brothers, Orville (left) and Wilbur (right), taken in 1905. Wilbur was about four years older than Orville. Image via Wikipedia (public domain).

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The story of the Wright brothers

Were the Wright brothers destined for the skies? It’s known that their father gave them a rubber-band-powered flying toy when they were still children. The toy was made of cork and bamboo with a paper body.

By 1899 – when Wilbur was 33 years old and Orville was 28 – the brothers were already learning everything they could about the science of aeronautics and the history of attempted human flight. Their first airplanes were gliders, which they tested on the long, isolated beaches of Kitty Hawk.

By 1902, they had built a glider that could be manned and controlled by a human pilot. It held a world record for gliding over 200 yards (about 183 meters).

Their first powered aircraft had a little over a 40-foot (12-meter) wingspan, weighed 750 lbs (340 kg), and had a 12-horsepower engine.

That first flight in December 1903 marked the beginning of a new era of global travel and interrelatedness.

By the time they received their patent for their airplane in 1906, several other aviators of the day claimed to have been the first to use the Wrights’ method of turning the airplane by warping or twisting the wings. But this part of the design, too, was included in the Wrights’ patent. In 2013, a story came to light about another would-be aviator, Gustave Whitehead, whose first flight supposedly beat the Wright brothers by two years. Thus far, that story has not been supported and is not accepted by aviation scholars.

Bottom line: The Wright brothers flew their first airplane for 12 seconds over 40 yards (about 37 meters) of sandy ground just outside Kitty Hawk, North Carolina, on December 17, 1903.

The post The Wright brothers succeeded 120 years ago first appeared on EarthSky.

Meteor shower guide: Up next the Ursids and the Quadrantids

Editors of EarthSky — Sun, 17 Dec 2023 06:27:43 +0000

Now that winter is almost here, we can look forward to the last meteor shower of the year. Next up are the December Ursids.and January Quadrantids

Meteor shower around the December solstice … the Ursids

Predicted peak: is predicted** for December 23, 2023, at 4 UTC.
When to watch: Watch for Ursid meteors in the early morning hours of December 22 and 23.
Duration of shower: Ursids range from December 13 to 24, so you might see some intermingling with the Geminids’ peak.
Radiant: Circumpolar at northerly latitudes.
Nearest moon phase: A 1st quarter moon occurs at 18:39 UTC on December 19. So the waxing gibbous moon – at 86% illumination – may interfere with the Ursids in 2023 until the moon sets about three hours before sunrise.
Expected meteors at peak, under ideal conditions: Under a dark sky with no moon, the Ursids offer perhaps five to 10 meteors per hour.
Note: This low-key meteor shower – which always peaks around the solstice – is somewhat overlooked due to the holiday season. Its hourly rate is lower than that of the popular Geminid shower, which peaks over a week before.

The Ursids are named for their radiant point in the constellation Ursa Minor, which contains the Little Dipper. And the Little Dipper contains the North Pole. So for the Northern Hemisphere, the radiant is above the horizon all night long. Chart via Chelynne Campion/ EarthSky.

Early January 2024 meteors … the Quadrantids

When to watch: The best night for the 2024 Quadrantids is January 3-4 (The predicted peak** is 12:53 UTC on January 4). A bright last quarter moon will rise around midnight and shine the rest of the night. Try late night January 3 to dawn January 4, in moonlight.
Nearest moon phase: Last quarter moon will come late on January 3, 2024 (CST).
Radiant: Rises in the north-northeast after midnight and is highest up before dawn. The radiant point for the Quadrantids is in a now-obsolete constellation, Quadrans Muralis the Mural Quadrant. Nowadays, we see the radiant near the famous Big Dipper asterism. Because the Quadrantid radiant is far to the north on the sky’s dome, this is mostly a far-northern shower, not as good for the Southern Hemisphere.
Expected meteors at peak, under ideal conditions: Under a dark sky with no moon, when the radiant is high in the sky, the Quadrantids can (briefly) produce over 100 meteors per hour.
Duration of shower: The Quadrantid meteor shower runs from mid-November through mid-January each year, according to this 2017 article in the journal Icarus. You might see a Quadrantid streak by any time during that interval. But most activity is centered on the peak.
Note: The Quadrantid shower is one of four major meteor showers each year with a sharp peak (the other three are the Lyrids, Leonids, and Ursids).

The radiant point for the Quadrantid meteor shower is far to the north in the sky and so best seen from Earth’s Northern Hemisphere. From mid-northern latitudes, the radiant point for the Quadrantid meteor shower climbs over the horizon after midnight and is highest up before dawn.

April 2024 meteors … the Lyrids

When to watch in 2024: Late evening April 21 until dawn April 22 will be best. The predicted** peak is 9:23 UTC on April 22. The peak of the Lyrids is narrow (no weeks-long stretches of meteor-watching, as with some showers). In 2024, the full moon falls at 23:49 UTC on April 23. So meteor watching will be impacted by a bright waxing gibbous moon.
Radiant: Rises before midnight, highest in the sky at dawn.
Nearest moon phase: Full moon falls at 23:49 UTC on April 23. So a bright waxing gibbous moon will be in the sky during the peak morning for the 2023’s Lyrid meteor shower.
Duration of shower: April 15 to April 29.
Expected meteors at peak, under ideal conditions: In a dark sky with no moon, you might see 10 to 15 Lyrids per hour. The Lyrids are known for uncommon surges that can sometimes bring rates of up to 100 per hour! Read more about Lyrid outbursts.
Note for Southern Hemisphere: This shower’s radiant point is far to the north on the sky’s dome. So the Southern Hemisphere will see fewer Lyrid meteors. Still, you might see some!

Lyrid meteors radiate from near the bright star Vega in the constellation Lyra the Harp. You don’t need to identify Vega or Lyra in order to watch the Lyrid meteor shower. But you do need to know when the radiant rises, in this case in the northeast before midnight. That’s why the Lyrids are typically best between midnight and dawn.

May 2024 meteors … the Eta Aquariids

When to watch: New moon will fall a few days after the peak of the 2024 Eta Aquariid shower. So, mornings around the peak will be dark and moonless. The best mornings to watch are May 5 and 6, 2024, in the hours before dawn. Why before dawn? See “Radiant” below.The American Meteor Society is listing 8:43 UTC on May 5 as the shower’s predicted** peak time. But times vary between different experts. And the peak of this shower stretches out over several days. So you can expect elevated numbers of meteors a few days before and after the peak time.
Nearest moon phase: New moon will fall at 03:22 UTC on May 8. So moonlight will not obscure the 2024 Eta Aquariids.
Radiant: Will rise in the wee hours, climbing toward its highest point at dawn. That’s why before dawn will be the best time to watch this shower.
Duration of shower: April 15 to May 27.
Expected meteors at peak, under ideal conditions: In the southern half of the U.S., you might see 10 to 20 meteors per hour under a dark sky, with no moon, when the radiant is high in the sky. Farther south – at latitudes in the Southern Hemisphere – you might see two to three times that number.
Note: The Eta Aquariids’ radiant will be on the ecliptic, which will ride low in the sky on spring mornings as seen from the Northern Hemisphere. That’s why this shower favors the Southern Hemisphere. It’s often that hemisphere’s best meteor shower of the year.

The radiant point of the Eta Aquariid meteor shower will be near the star Eta Aquarii in the constellation Aquarius the Water Bearer. The radiant will rise in the wee hours after midnight and will continue climbing toward its highest point at dawn. That highest point will be in the south as viewed from the Northern Hemisphere, closer to overhead for the Southern Hemisphere. That’s why the Southern Hemisphere will see more meteors (the radiant will be higher up), and it’s why – for all of us around the globe – the hours before dawn will be best for this shower.

June 2024 daytime meteor shower … the Arietids

Most meteor showers are easy to observe. Just find a dark sky, and look up! But what about meteor showers that happen in the daytime, when the sun is up? The Arietids are sometimes said to be the most active daytime meteor shower. In 2024, their predicted** peak will be the morning of June 7. You might catch some Arietids that morning in the dark hour before dawn.

When to watch: Watch from May 29 to June 17. There’s a predicted** peak on June 7, 2024. Watch for them in the sunrise direction in the dark hour before dawn breaks.
Nearest moon phase: In 2024, a new moon occurs at 12:38 UTC on June 6. So the mornings around the peak will be completely moon free.
Radiant: The shower’s radiant point – the point in the sky from which the meteors appear to radiate – is in the constellation Aries the Ram. You’ll find this constellation in the east before sunrise.
Duration of shower: May 29 to June 17.
Expected meteors at peak: This is tricky for daytime meteor showers because once the sun comes up, you won’t be able to see them. But the Arietids have a strong zenithal hourly rate (ZHR)! Meteor counts with radar and radio echoes have indicated a rate of 60 meteors per hour, and perhaps as high as 200 meteors per hour.
Note: The Arietids are sometimes said to be the most active daytime meteor shower.

The Arietids are an active shower, but they’re visible mostly in daytime. Watch for them in the sunrise direction in the dark hour before dawn from May 29 to June 17. You’ll be looking for meteors that shoot up from the horizon. The radiant is below the constellation Aries the Ram. Chart by John Jardine Goss.

Late July to mid-August 2024 meteors … the Delta Aquariids

Predicted peak: The peak is predicted** for July 30, 2024, at 15:16 UTC. But this shower doesn’t have a noticeable peak. It rambles along steadily from late July through early August, joining forces with the August Perseids.
When to watch: Watch late July through early August, mid-evening to dawn.
Duration of shower: July 18 to August 21.
Radiant: Rises in mid-evening, highest around 2 a.m. and low in the sky by dawn. See chart below.
Nearest moon phase: In 2024, last quarter moon falls at 2:51 UTC on August 1. Take advantage of the moon-free evenings in late July for watching the Delta Aquariids (and the early Perseids).
Expected meteors at peak, under ideal conditions: The Delta Aquariids’ maximum hourly rate can reach 15 to 20 meteors in a dark sky with no moon. You’ll typically see plenty of Delta Aquariids mixed in with the Perseids, if you’re watching in early August.
Note: Like May’s Eta Aquariids, July’s Delta Aquariids favors the Southern Hemisphere. Skywatchers at high northern latitudes tend to discount it. But the shower can be excellent from latitudes like those in the southern U.S. Delta Aquariid meteors tend to be fainter than Perseid meteors. So a moon-free dark sky is essential. About 5% to 10% of the Delta Aquariid meteors leave persistent trains, glowing ionized gas trails that last a second or two after the meteor has passed.

Delta Aquariid meteors radiate from near the star Skat, aka Delta Aquarii, in the constellation Aquarius the Water Bearer. This star is near bright Fomalhaut. In late July to early August, Fomalhaut is highest around 2 a.m. (on your clock no matter where you are). It’s southward from the Northern Hemisphere, closer to overhead from the Southern Hemisphere. Fomalhaut appears bright and solitary in the sky. To find it, draw a line roughly southward through the stars on the west side of the Great Square of Pegasus.

Mid-July to mid-August 2024 meteors … the Perseids

Predicted peak: The peak is predicted** for August 12, 2024, at 14:00 UTC. So the mornings of August 11, 12 and 13 are probably your best bet.
When to watch: The moon will be a 1st quarter and 50% illuminated during 2024’s peak of the Perseid meteor shower. So the best time to watch for Perseids will be starting around midnight until dawn. This shower rises to a peak gradually, then falls off rapidly. And Perseid meteors tend to strengthen in number as late night deepens into the wee hours before dawn. The shower is often best just before dawn.
Radiant: The radiant rises in the middle of the night and is highest at dawn. See chart below.
Nearest moon phase: First quarter moon falls at 15:19 UTC on August 12. And a 1st quarter moon sets around midnight, so you’ll have dark skies after then until dawn.
Duration of shower: July 14 to September 1.
Expected meteors at peak, under ideal conditions: Under a dark sky with no moon, skywatchers frequently report 90 meteors per hour, or more. In 2023, the waning crescent moon will not interfere with the meteor shower.
Note: The August Perseid meteor shower is rich and steady, from early August through the peak. The meteors are colorful. And they frequently leave persistent trains. All of these factors make the Perseid shower perhaps the most beloved meteor shower for the Northern Hemisphere.

Perseid meteors radiate from a point in the constellation Perseus the Hero. The radiant rises in late evening and is highest at dawn. Remember … you don’t have to find a shower’s radiant point to see meteors. The meteors will be flying in all parts of the sky.

Early October meteors … the Draconids

Predicted peak: The peak is predicted** for October 8, 2024, at 3 UTC.
When to watch: The best time to watch the Draconids in 2024 is the evening of October 7 through the wee hours of the morning on October 8. The waxing crescent moon (27% illuminated) will set before 9 p.m. your local time. So you can watch for meteors in a moonless sky.
Overall duration of shower: October 6 through 10.
Radiant: Highest in the sky in the evening hours. See chart below.
Nearest moon phase: First quarter moon is 18:55 UTC on October 10.
Expected meteors at peak, under ideal conditions: Under a dark sky with no moon, you might catch 10 Draconid meteors per hour.
Note: The Draconid shower is a real oddity, in that the radiant point stands highest in the sky as darkness falls. That means that, unlike many meteor showers, more Draconids are likely to fly in the evening hours than in the morning hours after midnight. This shower is usually a sleeper, producing only a handful of languid meteors per hour in most years. But watch out if the Dragon awakes! In rare instances, fiery Draco has been known to spew forth many hundreds of meteors in a single hour. That possibility keeps many skywatchers outside – even in moonlight – during this shower.

The radiant point for the Draconid meteor shower almost coincides with the head of the constellation Draco the Dragon in the northern sky. That’s why you can view the Draconids best from the Northern Hemisphere. This chart faces northward at nightfall in October. The Big Dipper sits low in the northwest. From the southern U.S. and comparable latitudes, in October, obstructions on your northern horizon might hide the Big Dipper from view. From farther south – say, the Southern Hemisphere – you won’t see the Dipper at all in the evening at this time of year. But, if you can spot it low in the sky, use the Big Dipper to star-hop to the star Polaris. Polaris marks the end star in the handle of the Little Dipper. Got all these stars? Then you should also be able to spot Eltanin and Rastaban, the Draconids’ radiant point, high in the northwest sky at nightfall in early October. Draconid meteors radiate from near these stars, which are known as the Dragon’s Eyes.

Late October meteors … the Orionids

Predicted peak: The peak is predicted** for October 20, 2024, at 18:14 UTC.
When to watch: Watch for Orionid meteors on both the mornings of October 20 and 21, starting after midnight through the wee hours before dawn.
Overall duration of shower: September 26 to November 22.
Radiant: The radiant rises before midnight and is highest in the sky around 2 a.m. See chart below.
Nearest moon phase: The full moon falls at 11:26 UTC on October 17. So, at the Orionids’ peak, the the waning gibbous moon will interfere with the meteor shower.
Expected meteors at peak, under ideal conditions: Under a dark sky with no moon, the Orionids exhibit a maximum of about 10 to 20 meteors per hour.
Note: These fast-moving meteors occasionally leave persistent trains. The Orionids sometimes produce bright fireballs.

If you trace Orionid meteors backward on the sky’s dome, they seem to radiate from the upraised club of the famous constellation Orion the Hunter. This is the shower’s radiant point. The bright star near the radiant point is reddish Betelgeuse. Chart via Chelynne Campion/ EarthSky.

October into early November … the South and North Taurids

Predicted peak: The South Taurids’ predicted** peak is November 5, 2024, at 7:00 UTC. The North Taurids’ predicted** peak is November 12, 2024, at 6:00 UTC. Both the South and North Taurids don’t have very definite peaks. They ramble along in October and November and are especially noticeable from late October into early November, when they overlap.
When to watch: Best around midnight, and on the days around November 5 when the moon won’t interfere.
Overall duration of shower: The South Taurids run from about September 23 to November 12. North Taurids are active from about October 13 to December 2.
Radiant: Rises in early evening, highest in the sky around midnight. See chart below.
Nearest moon phases: In 2024, the first quarter moon falls on November 9. The new moon is November 1, and it’s before the predicted peak of the South Taurids on November 5, so the days around then will be the best days to watch for Taurid meteors. However, the waxing crescent moon – 3 days before a full moon – will interfere with most meteors around the November 12 peak of the North Taurids. You’ll catch Taurid meteors throughout October and November. Visit Sunrise Sunset Calendars to see moon rising times for your location. Be sure to check the moon rising time box.
Expected meteors at peak, under ideal conditions: Under dark skies with no moon, both the South and North Taurid meteor showers produce about five meteors per hour (10 total when they overlap). Also, watch for fireballs.
Note: Taurid meteors tend to be slow-moving but sometimes very bright. The showers sometimes produce fireballs, which made their cyclical reappearance in 2022. The American Meteor Society pointed to “a seven-year periodicity” with Taurid fireballs. 2008 and 2015 both produced them. 2022 did as well. The Taurid fireball display, in 2015, was really fun! Photos and video of 2015 Taurid fireballs here.

The Taurid meteors consist of 2 streams, the South Taurid meteors and North Taurid meteors. Both streams appear to originate from the constellation Taurus the Bull. Typically, you see the maximum numbers at or around midnight, when Taurus is highest in the sky.

Mid-November meteors … the Leonids

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Predicted peak: The peak is predicted** for November 18, 2024, at 5:00 UTC.
When to watch: Watch late on the night of November 17 until dawn on November 18. The morning of November 17 might be worthwhile, too.
Duration of shower: November 3 through December 2.
Radiant: Rises around midnight, highest in the sky at dawn.
Nearest moon phase: In 2024, the full moon falls on November 15. So the bright waning gibbous moon will wash out some meteors in 2024.
Expected meteors at peak, under ideal conditions: Under a dark sky with no moon, you might see 10 to 15 Leonid meteors per hour.
Note: The famous Leonid meteor shower produced one of the greatest meteor storms in living memory. Rates were as high as thousands of meteors per minute during a 15-minute span on the morning of November 17, 1966. That night, Leonid meteors did, briefly, fall like rain. Some who witnessed it had a strong impression of Earth moving through space, fording the meteor stream. Leonid meteor storms sometimes recur in cycles of 33 to 34 years. But the Leonids around the turn of the century – while wonderful for many observers – did not match the shower of 1966. And, in most years, the Lion whimpers rather than roars.

Leonids stream from a single point in the sky – their radiant point – in the constellation Leo the Lion. Leo rises just before midnight in mid-November. Regulus, the brightest star in Leo the, dots a backwards question mark of stars known as the Sickle.

Early to mid-December meteors … the Geminids

Predicted peak: is predicted** for December 13, 2024, at 21:00 UTC.
When to watch: Since the radiant rises in mid-evening, you can watch for Geminids all night around the peak dates of December 13. However, an almost full moon will compete with the Geminids in 2024. Luckily, a lot of Geminid meteors are bright. Find a way to block out the bright moon when watching the sky.
Overall duration of shower: November 19 to December 24.
Radiant: Rises in mid-evening, highest around 2 a.m. See chart below.
Nearest moon phase: In 2024, the full moon falls on December 15. So there will be a moonlit sky during the peak of the 2023 Geminid meteor shower.
Expected meteors at peak, under ideal conditions: Under a dark sky with no moon, you might catch 120 Geminid meteors per hour.
Note: The bold, white, bright Geminids give us one of the Northern Hemisphere’s best showers, especially in years when there’s no moon. They’re also visible, at lower rates, from the Southern Hemisphere. The meteors are plentiful, rivaling the August Perseids.

Geminid meteors radiate from near the bright star Castor in the constellation Gemini the Twins, in the east on December evenings.

Meteor shower-watching resources

How high up are meteors when they begin to glow?

Find a Dark Sky Place, from the International Dark Sky Association

Heavens-Above: Satellite predictions customized to your location

Stellarium Online: Star maps customized to your location

Dark Site Finder, from astrophotographer Kevin Palmer

Blue Marble Navigator

EarthSky’s tips for meteor-watchers

Why do meteor showers have a radiant point?

RASC Observer’s Handbook, an indispensable tool for stargazers. The peak dates dates and times listed in this article are (mostly) from there

Meteor shower guide: photos from the EarthSky community

View at EarthSky Community Photos. | Photographer Thomas Hollowell in Colorado caught these Lyrid meteors on the morning of April 22, 2020, and said: “The 6 meteors in this frame were stacked in Photoshop on a set of 3 background frames.” Thanks, Thomas!

Draconids near Tucson, Arizona, in 2013, by our friend Sean Parker Photography.

James Younger sent in this photo during the 2015 peak of the Leonid meteor shower. It’s a meteor over the San Juan Islands in the Pacific Northwest.

View at EarthSky Community Photos. | William Mathe captured this image on December 20, 2019, in Lindon, Colorado. He wrote: “My wife and I made a 100-mile jaunt out into the eastern plains to try to capture one or more meteors from the Ursid meteor shower. We took this image facing due north. As you can see, just to the right of the little white church is Ursa Major pointing up to Polaris, and just to the left is a green ‘fireball’ meteor that lit up the sky for a second or two.” Thank you, William!

Quadrantid radiant composite via Scott MacNeill of Frosty Drew Observatory in Charleston, Rhode Island.

Meteor shower words of wisdom

A wise person once said that meteor showers are like fishing. You go, you enjoy nature … and sometimes you catch something.

Bottom line: We’ve got several more meteor showers this year. Next up are the Geminds followed by the Ursids. Your 2023 meteor shower guide here.

**Peak times for meteor showers provided by Robert Lunsford of the American Meteor Society. Note that predictions for meteor shower peak times may vary. Back to top.

The post Meteor shower guide: Up next the Ursids and the Quadrantids first appeared on EarthSky.

What’s a green flash and how can I see one?

Editors of EarthSky — Thu, 07 Dec 2023 10:00:44 +0000

What’s a green flash? Watch this video to learn more.

What is a green flash?

A sunset walk on a beach – looking west – is a great time to catch a green flash. What is it? The green flash is an optical phenomenon that you can see shortly after sunset or before sunrise. It happens when the sun is almost entirely below the horizon, with the upper edge still visible. For a second or two, that upper rim of the sun will appear green in color (or sometimes blue). It’s a brief flash of the color green, and quite exciting to see, especially if you’ve been looking for one!

Green flashes do play a role in some legends. In fact, it’s said that once you’ve seen a green flash, you’ll never again go wrong in matters of the heart.

The 2024 lunar calendars are here! Best Christmas gifts in the universe! Check ’em out here.

Mock mirage and green flash over the Pacific, seen by Jim Grant in San Diego. Published with permission.

How can you see one?

You just need two things to see a green flash:

1. A clear day with no haze or clouds on the horizon.
2. A distant horizon, and a distinct edge to the horizon. In particular, you can see the green flash from a mountaintop or high building. But usually, people on the beach or in boats see them over the ocean.

Important tip: Don’t look at the sun until it is nearly entirely below the horizon. If you do, you will dazzle (or damage) your eyes and ruin your green flash chances for that day.

Because you need to know exactly where to look along the horizon, and because most of us aren’t up before dawn, green flashes are most often seen after sunset. Diligent observers, however, can see them before dawn, too. And it’s possible to see green flashes over land, too, if your horizon is far enough away.

View at EarthSky Community Photos. | Jan Null took this photo on July 21, 2023, from Pigeon Point, California. Jan wrote: “Photographing Pigeon Point Lighthouse and capturing the green (and occasionally blue) flash are 2 of my favorite subjects on the San Mateo County Coast of California. There was slight inversion on one of the few fog-free days this summer. I drove there hoping to possibly catch one or the other. Fortunately, I was able to get both with probably the most distinct blue color I have seen, with a very strong blue spike on the histogram.” Thank you, Jan!

What makes a green flash?

According to Les Cowley at Atmospheric Optics:

As the sun’s disk diminishes, the green light becomes concentrated and separates from the other colors, creating the brilliant green flash that captivates observers.

During a green flash, our atmosphere distorts light from the sun as it sets, and the green rays are what reaches our eyes. Image via John Jardine Goss/ EarthSky/ Patrick Meyers.

Les explains that the green flash is part of a mirage:

Inferior mirages are produced by warm air at the ocean or earth’s surface and an air temperature gradient changing rapidly with height. Rays from a low sun are refracted back upward as they pass between the cool and warm layers. Refraction always tends to deflect rays toward the denser layer. An observer above the layer sees two solar images or parts of them … (1) an erect image from rays that pass relatively undeflected above the warm layer and (2) a lower inverted image from rays mirrored upward by the warm layer. Each sun image is as ‘real’ as the other. The effect is not dissimilar to the mirage seen above a hot road surface.

As the sunset proceeds, the upper and lower images approach, touch and eventually overlap to form an ‘omega’ shaped sun.

A green flash occurs because at a later stage the deflection by the warm layer/cooler air boundary becomes very sensitive to the angle of incidence of the sun’s rays. Small deviations are vertically magnified including the difference in deflection between red and green rays. This amplification provides the separation between green and red that refraction through a normal atmosphere cannot accomplish.

What is the green ray?

The flash can be like a flame that shoots above the horizon. In that case, it’s called a green ray. I’ve seen lots of green flashes, but never a green ray, although I was once walking on a beach in Mexico and turned away just as my companion saw one.

I did not find any photos of flamelike green rays (if you know of one, let me know), but the photo below suggests the beginnings of a ray.

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Mock mirage (explained at Atmospheric Optics) and green flash seen from San Francisco. Image via Brocken Inaglory/ Wikimedia Commons (CC BY-SA 4.0).

A green flash on other planets?

Well … Yes! You can also see a green flash on very bright planets – like Venus or Jupiter – from Earth. Check these amazing videos, and don’t miss the comment section below them. People had some very interesting questions to ask, and the authors gave them the answers they were looking for.

Green flash photos from the EarthSky community

View at EarthSky Community Photos. | Julee Vaughan in Ocean Beach, San Diego, California, captured this green flash on November 11, 2023. Julee wrote: “This was one of three green flash shots I got Saturday, Mother Nature put on a show!” Thank you, Julee!

View at EarthSky Community Photos. | Luka Milevoj in Skitaca, Croatia, captured this green flash on November 23, 2023. Thank you, Luka!

View at EarthSky Community Photos. | Julee Vaughan caught this green flash at Ocean Beach Fishing Pier, San Diego, California, on July 14, 2023. She commented: “A lot of people think the flash is just a myth, but it isn’t. It’s very real.” So true! Thanks, Julia!

View at EarthSky Community Photos. | Jim Grant caught this green flash at the Ocean Beach Pier in San Diego, California, on July 19, 2023. Jim wrote: “This sailboat was drifting close to the Ocean Beach Pier, I knew the sunset was going to be stunning, and I started tracking the boat, hoping to get it centered in the sun. The green rim and green flash above were a bonus.” Thank you, Jim!

A few more green flash photos

View at EarthSky Community Photos. | Jim Grant in San Diego, California, captured this green flash on July 12, 2023. Jim wrote: “I took this from an elevated deck directly across the street from the Ocean Beach Pier. I was 40 feet above sea level on a pretty clear day with a slight inversion layer in place.” Thank you, Jim!

View larger at EarthSky Community Photos. | Bill Miller caught this green flash in Sint Maarten on April 27, 2020. He wrote: “We see green flashes frequently, but it is always a challenge to get a good picture of one … timing is everything.” Thanks, Bill!

Green flash atop sun pyramid, in 2014, via Colin Legg. Used with permission.

View at EarthSky Community Photos. | Jim Grant at the Ocean Beach Pier, San Diego, California, captured took this image on December 8, 2023, and wrote: “I have been trying to capture the green flash with birds in the image for a few months finally all the pieces fell into place.” You nailed it! Thank you, Jim.

More great green flash photos

View at EarthSky Community Photos. | Meiying Lee in Mount Hehuan, Nantou, Taiwan, captured these images on January 31, 2023. Meiying wrote: “The last 6 seconds of sunset. When the sun has fallen below the horizon, we can continue to see sunlight because of atmospheric refraction. In the last few seconds, when there is only 1 line of sunlight left, because of the different refractive indices of various colors of light, we can see different colors of light … yellow, green and blue are arranged on that line like pearls!” Thank you, Meiying!

View at EarthSky Community Photos. | Jim Grant in San Diego, California, captured this series showing the green flash on February 19, 2020. Thank you, Jim!

View at EarthSky Community Photos. | Cecille Kennedy on the Oregon Coast captured this image on September 21, 2023. Cecille wrote: “The green flash appeared on top of the fiery red sun as it was setting on the ocean horizon. Over the sun the birds flying south are brown pelicans migrating to South California and Mexico.” Thank you, Cecille!

Bottom line: Learn what a green flash is and how to see one here. Plus, enjoy great photos and watch a video!
The post What’s a green flash and how can I see one? first appeared on EarthSky.

Kelvin-Helmholtz clouds look like ocean waves

Editors of EarthSky — Sun, 03 Dec 2023 11:33:40 +0000

Watch this video to learn more about wave clouds, or Kelvin-Helmholtz clouds.

Clouds that look like waves are rare and beautiful. These clouds – known as Kelvin-Helmholtz clouds, billow clouds, or shear-gravity clouds – might have been the inspiration for Van Gogh’s painting Starry Night. The next time you spot one of these remarkable wave clouds, capture a photograph and submit it to us!

Kelvin-Helmholtz clouds are named for Lord Kelvin and Hermann von Helmholtz, who studied the physics of the instability that leads to this type of cloud formation. A Kelvin-Helmholtz instability forms where there’s a velocity difference across the interface between two fluids: for example, wind blowing over water.

The 2024 lunar calendars are here! Best Christmas gifts in the universe! Check ’em out here.

How to see Kelvin-Helmholtz clouds

When might you get to see these beautiful clouds? Your odds are better on windy days, when there’s a difference in densities of the air – for example, during a temperature inversion – when warm air flows over cooler air. You’re also more likely to see these clouds near sunrise or sunset, another time when the bottom of the clouds are cooler and the air above is warmer. The clouds take on this wave shape when the air above is moving more quickly than the air below, pushing over the tops of the clouds and creating the rolling wave appearance. As you might have guessed, Kelvin-Helmholtz clouds are a sign that aircraft in the area will be experiencing turbulence.

View at EarthSky Community Photos. | EarthSky’s own Raúl Cortés captured these Kelvin-Helmholtz clouds from an airplane near Amsterdam on February 21, 2023. See the wave-shaped clouds above the gap? Thank you, Raúl!

Wave clouds from the EarthSky community

View at EarthSky Community Photos. | Grant Spratt in Surfers Paradise, Queensland, Australia, captured this view of wave clouds on November 29, 2023. Grant wrote: “View to south, chance of severe thunderstorm warning.” Thank you, Grant!

View at EarthSky Community Photos. | Lori Mendez in Saint Helena, California, captured these Kelvin-Helmholtz clouds on November 13, 2023. Lori wrote: “Always beautiful sunsets from my work view. Leaving work tonight, everyone was taking pictures of these clouds. I have never seen clouds like this. I posted to Facebook and someone sent your link saying what they are called.” Thank you, Lori!

View at EarthSky Community Photos. | Karen Gord in Mosheim, Tennessee, captured these wave clouds on November 15, 2023. Karen wrote: “A frosty, crisp 29-degree morning. The clouds caught my attention out the window. Beautiful. Never seen this before.” Thank you, Karen!

View at EarthSky Community Photos. | Linda K. Tilley in Wyoming captured these Kelvin-Helmholtz clouds on November 11, 2023. Thank you, Linda!

View at EarthSky Community Photos. | Kevin Horath took this image on October 12, 2023. Kevin wrote: “While sailing off the coast of Maine, I saw clouds that looked like waves.” Thank you, Kevin!

More photos of Kelvin-Helmholtz clouds

View at EarthSky Community Photos. | Early on the morning of May 23, 2021, Angus Weller spotted these Kelvin-Helmholtz clouds over the Coastal Mountain Range just north of Vancouver, British Columbia. Angus said: “It’s only the 2nd time I’ve seen this cloud formation.” Thank you, Angus!

View at EarthSky Community Photos. | Michelle Berger in Sandpoint, Idaho, captured this photo of Kelvin-Helmholtz clouds on December 27, 2020. She wrote: “We were driving home one evening in December, 2 days after Christmas, and saw this beautiful image in the sky east of our way home.” Thank you, Michelle!

View at EarthSky Community Photos. | Suzanne Kelley of Littleton, Colorado, caught these Kelvin-Helmholtz clouds – clouds that look like ocean waves – at sunset over the Rocky Mountains on New Year’s Eve, December 31, 2019. Thank you, Suzanne!

View at EarthSky Community Photos. | Matty Hammersley in the UK wrote: “Taken by my wife Ems whilst I was driving south on M5, south of Birmingham/Black Country toward Worcestershire area.” The image is from around sunset, on March 28, 2022. The clouds are known as Kelvin-Helmholtz clouds. Thank you, Matty!

Kelvin-Helmholtz clouds from 2 sides of Earth

These photographers both captured Kelvin-Helmholtz clouds on the same day, from two sides of Earth.

View at EarthSky Community Photos. | Tim Hunter in Waitara, Taranaki, New Zealand, captured this photo of wave clouds on October 6, 2021. He wrote: “Was chatting to my father on the phone in my lounge, stood up from the couch, looked out the window and saw 2 waves and more forming. The formations lasted about a minute and a half before fading away. It was a beautiful sight. One I may never get to witness again.” Thank you, Tim!

View at EarthSky Community Photos. | Julie Hinder in Slapton, Devon, UK, captured this photo of wave clouds on October 6, 2021. Thank you, Julie!

Wave clouds on other planets

Earth isn’t the only planet with Kelvin-Helmholtz clouds. Here they are on Saturn; Jupiter has them, too. Image via NASA/ Wikimedia Commons (public domain).

Bottom line: Clouds that look like waves across the sky are known as Kelvin-Helmholtz clouds. These clouds form from winds moving at two different speeds.
The post Kelvin-Helmholtz clouds look like ocean waves first appeared on EarthSky.

Look for Mercury after sunset, early December 2023

Editors of EarthSky — Fri, 01 Dec 2023 11:00:34 +0000

On December 4, Mercury reaches its farthest angular distance from the sun, known as greatest eastern elongation. On this date, it lies low in the southwest. Chart via John Jardine Goss/ EarthSky.

Mercury will reach its greatest elongation – its greatest apparent distance from the sun on the sky’s dome for this evening apparition – on December 4, 2023.

Mercury after sunset in late 2023

Where to look: Look west, in the sunset direction – shortly after sunset – for Mercury. The sun’s innermost planet will be challenging, even when Mercury is farthest from the sunset, and even for the more favored view from the Southern Hemisphere.
Greatest elongation: Mercury is farthest from the sun on ou4 sky’s dome – at greatest elongation – at 14 UTC on December 4, 2023 (8 a.m. CDT on December 4). At that time, Mercury is 21 degrees from the sun in our sky.
Brightness: Mercury was bright when it emerged in the evening sky during the second week of November. At that time, it was shining at -0.5 magnitude. At greatest elongation, Mercury shines only slightly more faintly at magnitude -0.3. It’s still brighter than most stars! In the evenings after greatest elongation, the innermost planet will rapidly fade as it sweeps up from behind Earth, in orbit around the sun, causing its illuminated side, or day side, to turn away from us. It’ll probably disappear by mid-December 2023 and will reach inferior conjunction – when it will pass between Earth and the sun – on December 22.
Through a telescope: Mercury will appear about 62% illuminated, at greatest elongation. It’ll measure 6.7 arcseconds across.
Constellation: Mercury will lie in front of the constellation Sagittarius the Archer at this elongation. Doubtless, most of the stars in this constellation will be lost in the twilight.
Note: As the innermost planet, Mercury is tied to the sun in our sky. As a result, it never ventures very far above the horizon after sunset. So as soon as the sun disappears below your horizon, your clock starts ticking. Will you see the glowing point of light that is Mercury before it drops below the horizon, following the setting sun?

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At greatest elongation, Mercury is to one side of the sun and is at its greatest distance from the sun on our sky’s dome. Mercury reaches greatest eastern (evening) elongation from the sun on December 4, 2023. It is 21 degrees from the sun in the evening sky. Chart via John Jardine Goss/ EarthSky.

Finder charts for Northern Hemisphere evenings

For viewers in the Northern Hemisphere, Mercury will lie just above the horizon in the bright twilight shortly after sunset in the second half of November 2023. The Teapot asterism of Sagittarius is nearby but it will be difficult to spot in the bright evening twilight. Chart via John Jardine Goss/ EarthSky.

For viewers in the Northern Hemisphere, Mercury will lie just above the horizon in the bright twilight shortly after sunset in the first half of December 2023. Chart via John Jardine Goss/ EarthSky.

Viewers with a low southwestern horizon and clear skies will spot the very thin crescent moon floating in the bright twilight shortly after sunset on December 14 and 15, 2023. Mercury will lie to the moon’s lower right, very close to the horizon. Chart via John Jardine Goss/ EarthSky.

Finder charts for November Southern Hemisphere evenings

During the second half of November 2023, Mercury will lie low in the west below the Teapot asterism of Sagittarius shortly after sunset. Chart via John Jardine Goss/ EarthSky.

For viewers in the Southern Hemisphere, during the first half of December 2023, Mercury lies low in the west immediately below the Teapot asterism of Sagittarius shortly after sunset. Chart via John Jardine Goss/ EarthSky.

For precise sun and Mercury rising times at your location:

Old Farmer’s Almanac (U.S. and Canada)
timeanddate.com (worldwide)
Stellarium (online planetarium program)

Mercury events in 2023 and 2024

Note: Times are in UTC

Jan 7, 2023: Inferior conjunction (races between Earth and sun)
Jan 30, 2023: Greatest elongation (morning)
Mar 17, 2023: Superior conjunction (passes behind sun from Earth)
Apr 11, 2023: Greatest elongation (evening)
May 1, 2023: Inferior conjunction (races between Earth and sun)
May 29, 2023: Greatest elongation (morning)
Jul 1, 2023: Superior conjunction (passes behind sun from Earth)
Aug 10, 2023: Greatest elongation (evening)
Sep 6, 2023: Inferior conjunction (races between Earth and sun)
Sep 22, 2023: Greatest elongation (morning)
Oct 20, 2023: Superior conjunction (passes behind sun from Earth)
Dec 4, 2023: Greatest elongation (evening)
Dec 22, 2023: Inferior conjunction (races between Earth and sun)

Jan 12, 2024: Greatest elongation (morning)
Feb 28, 2024: Superior conjunction (passes behind sun from Earth)
Mar 24, 2024: Greatest elongation (evening)
Apr 11, 2024: Inferior conjunction (races between Earth and sun)
May 9, 2024: Greatest elongation (morning)
Jun 14, 2024: Superior conjunction (passes behind sun from Earth)
Jul 22, 2024: Greatest elongation (evening)
Aug 19, 2024: Inferior conjunction (races between Earth and sun)
Sep 5, 2024: Greatest elongation (morning)
Sep 30, 2024: Superior conjunction (passes behind sun from Earth)
Nov 16, 2024: Greatest elongation (evening)
Dec 5, 2024: Inferior conjunction (races between Earth and sun)
Dec 25, 2024: Greatest elongation (morning)

Heliocentric view of Mercury December 2023

View larger. | Heliocentric view of solar system, December 2023. Chart via Guy Ottewell Used with permission.

A comparison of elongations

The farthest from the sun that Mercury can ever appear on the sky’s dome is about 28 degrees. And the least distance is around 18 degrees.

Also, elongations are better or worse depending on the time of year they occur. So in 2023, the Southern Hemisphere had the best evening elongation of Mercury in August 2023. And the Northern Hemisphere had the best evening apparition in April.

In the autumn for either hemisphere, the ecliptic – or path of the sun, moon and planets – makes a narrow angle to the horizon in the evening. But it makes a steep slant, nearly perpendicular, in the morning. So, in autumn from either hemisphere, morning elongations of Mercury are best. That’s when Mercury appears higher above the horizon and farther from the glow of the sun. However, evening elongations in autumn are harder to see.

In the spring for either hemisphere, the situation reverses. The ecliptic and horizon meet at a sharper angle on spring evenings and a narrower angle on spring mornings. So, in springtime for either hemisphere, evening elongations of Mercury are best. Meanwhile, morning elongations in springtime are harder to see.

View larger. | Mercury elongations compared. Here, gray areas represent evening apparitions (eastward elongation). Blue areas represent morning apparitions (westward elongation). The top figures are the maximum elongations, reached at the top dates shown beneath. Curves show the altitude of the planet above the horizon at sunrise or sunset, for latitude 40 degrees north (thick line) and 35 degrees south (thin). Maxima are reached at the parenthesized dates below (40 degrees north in bold type). Chart via Guy Ottewell’s 2023 Astronomical Calendar. Used with permission.

More Mercury elongation comparisons for 2023

View larger. | Mercury’s greatest evening elongations in 2023 from the Northern Hemisphere as viewed through a powerful telescope. The planet images are at the 1st, 11th, and 21st of each month. Dots show the actual positions of the planet for every day. Chart via Guy Ottewell. Used with permission.

View larger. | Mercury’s greatest evening elongations in 2023 from the Southern Hemisphere as viewed through a powerful telescope. The planet images are at the 1st, 11th, and 21st of each month. Dots show the actual positions of the planet for every day. Chart via Guy Ottewell. Used with permission.

Mercury photos from our community

View at EarthSky Community Photos. | Joel Weatherly in Edmonton, Alberta, Canada, took this image on April 23, 2022. Joel wrote: “Lonely little Mercury is making an appearance in our evening skies. Despite being elusive, it was easy to see without optical aid once sighted.” Thank you, Joel!

View at EarthSky Community Photos. | Chix RC captured this image on January 3, 2022, from Hermosa Beach, California. See Mercury to the upper right of the crescent? Chix wrote: “A faint young moon at 1% illumination and Mercury.” Thank you, Chix!

View at EarthSky Community Photos. | Alexander Krivenyshev of the website WorldTimeZone.com captured this photo of the moon together with Mercury and Venus on May 13, 2021, from Newport, Rhode Island. Thank you, Alexander!

Bottom line: Mercury is visible in the evening sky. Look in the west as the sky is darkening. The planet will reach its greatest elongation overnight on December 4, 2023.

Submit your photos to EarthSky here.

Read about greatest elongations, superior and inferior conjunctions: Definitions for stargazers
The post Look for Mercury after sunset, early December 2023 first appeared on EarthSky.

EarthSky’s lunar calendar: How to use this great gift!

Editors of EarthSky — Fri, 01 Dec 2023 10:30:28 +0000

As your can see, EarthSky’s lunar calendar shows the moon phases for each day of the year.

The 2024 lunar calendars are here! Best Christmas gifts in the universe! Check ’em out here.

How to use EarthSky’s lunar calendar

EarthSky’s lunar calendar is a unique, beautiful, poster-sized calendar printed in lush silver on deep blue, providing the phases of the moon for every day of the year, and noting each month’s new and full moons. In fact, it shows the moon waxing from new to full, and waning from full to new. Plus, it’s gorgeous and it’s the best gift ever! What’s more, it’ll help you get in touch with nature. So what more could you ask for in a calendar?

Read the five tips below and enjoy your moon calendar.

1. First, get to know your lunar calendar

The horizontal row at the top represents the months of the year, and the vertical rows to the right and left give you the date. Yes, it’s just that simple.

The lunar calendar shows every day in every month of 2024. Available now!

2. Enjoy the moon’s cycle.

By the way, one cycle, from new moon to new moon, is called a lunar month or synodic month. The mean length of the phase cycle is 29.53059 days (29 days, 12 hours, and 44 minutes), though it can vary from about 29.3 to 29.8 days.

3. Each night, the lunar calendar shows the moon’s phase.

As a matter of fact, the phase of the moon will let you know if the moon will be out tonight, and when. At new moon the moon is not visible (unless it “blocks” out all or part of the sun during a solar eclipse). At first quarter the moon lights up the evening hours, setting in the west around midnight. Then at full moon the moon stays out all night long. Finally, at last quarter the moon rises in the east around midnight, and can be found in the morning sky. And it sets around noon.

4. Realize that the moon is a world in space.

Like Earth, it’s always half-lit by sunshine and half-engulfed in its own shadow. But the percentage of the moon’s daylight side that we see from Earth changes. The moon’s night side faces us at new moon. And its totally illuminated day side faces us at full moon. Then the terminator – the shadow line dividing the lunar day from the lunar night – shows you where it’s sunrise on the moon as the moon waxes from new to full. Conversely, it shows you where it’s sunset on the moon as the moon wanes from full to new.

Phases of the moon as it revolves around the Earth. Click here to see an animation. Image and animation via NASA/ Wikipedia (public domain).

5. Collect ’em.

Hold on to your EarthSky lunar calendars, even after the year has passed. Then, if you post them on your wall side by side, they make a very cool wave pattern. Plus … consider that the ancients discovered that 235 lunar (synodic) months almost exactly equal 19 years. That means the phases of the moon will recur – or nearly recur – on the same calendar dates 19 years from now. Cool!

So what are you waiting for?

Order your EarthSky lunar calendar today and enjoy a newfound appreciation for the lunar month and the intriguing cycle of lunar phases.

Order your EarthSky lunar calendar here.

View at EarthSky Community Photos. | Chantal Torchia from Old Bridge, New Jersey, took this image of the moon on December 29, 2022. She wrote: “As one year ends, going out of focus, the next one comes beautifully INTO focus.” Thank you, Chantal!

Bottom line: The EarthSky lunar calendar is beautiful. Plus, it’s the best gift ever! And it’ll help you get in touch with nature. Here’s why you need an EarthSky lunar calendar, the top tips for using it, and how to order one.

Order your EarthSky lunar calendar here.

Find EarthSky astronomy tools and gear at the EarthSky Store.
The post EarthSky’s lunar calendar: How to use this great gift! first appeared on EarthSky.

December birthstone: turquoise, zircon or tanzanite

Editors of EarthSky — Fri, 01 Dec 2023 10:01:01 +0000

The December birthstone, turquoise, from Nishapur in northeastern Iran. Image via Sonia Sevilla/ Wikimedia Commons.

If you’re born in December, you have a choice of three birthstones: turquoise, zircon and tanzanite. Turquoise, a soft gemstone used in jewelry and ornaments, has a rich history dating to antiquity. Zircons are not well-known gemstones, but they make absolutely stunning jewelry. Tanzanite is an exquisite clear blue-violet crystal found only in Tanzania.

Why do some months have one birthstone but others have two or three? According to the website onecklace.com, multiple stones for some months allow more affordable options in addition to the traditional and more expensive stones.

The 2024 lunar calendars are here! Best Christmas gifts in the universe! Check ’em out here.

December birthstone: turquoise

To chemists and geologists, turquoise is copper aluminum phosphate. It forms when rainwater or melted snow percolates through copper ore deposits called copper porphyry. Water interacts with copper sulfides in the ore to form an acidic solution. This copper-carrying acidic water, when it reacts with aluminum and potassium in the rocks, precipitates turquoise into cavities. You can find turquoise in weathered volcanic rock and sedimentary rock in arid locations.

Turquoise is a relatively soft gemstone, with a Mohs scale hardness of five to six. You can scratch or break turquoise with moderate force. Oil and pigments easily discolor this porous opaque stone. It also changes color when it loses some of its water content.

Hard, relatively non-porous, compact stones have the best appearance because the stone can be finely polished. “Softer” varieties that are more porous are treated with oil, paraffin, liquid plastic or water glass to enhance its durability and color.

Copper gives a sky-blue shade to turquoise, while iron gives it a greener tone. The most valued variety of turquoise is an intense sky-blue color, like the color of a robin’s egg. Ochre and brown-black veins, often found in the gemstones, are inclusions from the surrounding rock matrix.

Turquoise facts

Some of the best turquoise in the world comes from Iran, famous for its sky-blue stones from Neyshabur. In Egypt, people have mined turquoise in the Sinai Peninsula for over 5,000 years. Turquoise is found in many U.S. southwestern states: Arizona, California, Colorado, New Mexico and Nevada. This stone also occurs in Afghanistan, Australia, China, India, Tibet, Mexico and Brazil.

Turquoise from Cerillos, New Mexico, part of a collection at the Smithsonian Museum of Natural History. Image via Tim Evanson/ Wikimedia Commons.

The word turquoise originated from the French phrase pierre turquoise, meaning Turkish stone. That’s because Venetian traders brought the gemstone to Europe after acquiring it from traders in Turkey.

In antiquity, turquoise was used as jewelry by the ruling classes of civilizations in Africa, Asia and the Americas. People have found beads dating to the late 6th millennium BCE in ancient Iraq. Turquoise bracelets were on the arm of a woman in the tomb of Zer, a pharaoh that ruled Egypt around 3000 BCE. A 3,700-year-old dragon relic from the Xia Dynasty, made from over 2,000 pieces of turquoise, was in the tomb of a nobleman in central China.

Turquoise in the Americas

Turquoise has a rich history in the American Southwest. Native Americans have been using this gemstone to create jewelry and ornamental pieces for several thousand years. The Apache, Navajo, Pueblo, and Zuni are known for their turquoise jewelry.

In the Zuni language, the word for turquoise is sky stone. During the growing season in summer, Pueblo dancers wear turquoise to encourage rainfall. The Navajo associate turquoise with health and protection, using the stone in important rites of passage. While the Apache believed that turquoise lay at the end of a rainbow, and that turquoise attached to a bow or gun ensured an accurate aim.

Turquoise was a part of pre-Columbian cultures in Mexico, Central America, and South America. In Peru, prehistoric tribes made small objects such as beads, figurines and artifacts with turquoise inlays. For the Aztecs, turquoise was popular in ornaments. It also had important religious and ceremonial uses. For example, a high priest involved in human sacrifice wore a turquoise pendant hung from his underlip. A notable Aztec art form was intricate turquoise mosaics, like that of a turquoise mosaic mask used in the interment of a king.

Turquoise lore

Some people consider turquoise a love charm. When received as a gift, it is supposed to symbolize a pledge of affection. Shakespeare used this lore in “The Merchant of Venice.” In it, Leah gave a turquoise ring to Shylock when he was a bachelor, hoping it would win his affections so he would ask her to marry him.

There are many other superstitions associated with turquoise. In the twelfth century, an Arabian writing declared: “the turquoise shines when the air is pure and becomes pale when it is dim.” They also believed that its color changed with the weather. In the 13th century, people believed it would protect its owner from injury if he fell off a horse.

George Frederick Kunz’s book, The Curious Lore of Precious Stones, stated that diamonds and turquoises supposedly lost their powers if sold:

The spirit dwelling in the stone was thought to take offence at the idea of being bought and sold, and was supposed to depart from the stone, leaving it nothing more than a bit of senseless matter. If, however, the diamond (or turquoise) were offered as a pledge of love or friendship, the spirit was quite willing to transfer its good offices from one owner to another.

There were also health myths associated with turquoise. People believed the stone changed color when its wearer became ill. Some said it was an effective treatment for scorpion stings and pain from evil influences. Just looking at turquoise supposedly strengthen the eyes.

December birthstone: zircon

Several red zircon crystals embedded in a mostly quartz matrix. The entire piece measures about 2.1 cm (0.8 inches) in diameter. Image via Robert M. Lavinsky/ Wikimedia Commons.

Zircon is a mineral formed of the elements zirconium and silicon (zirconium silicate). Small crystals, just a few millimeters in size, are commonly found in most igneous rock. With a Mohs scale hardness of 7.5, zircon is hard enough to survive the geologic forces that create metamorphic and sedimentary rock. But large zircon crystals are rare. They’re formed mainly in pegmatites (coarse-grained igneous rock) and carbonatites. But due to weathering of gem-bearing rocks, most zircons are in alluvial and beach deposits.

The name zircon may have come from the Arabic words zarquin, meaning red. Or perhaps from the Persian word zargus, meaning gold-colored.

Major sources of gemstone-quality zircon are Thailand, Cambodia, Vietnam and Sri Lanka. The gemstones also occur in Myanmar, France, Norway, Australia and Canada.

Colors of zircon

Over vast spans of geologic time, forces have worked within zirconium silicate crystals to change their molecular structure and color. Uranium and thorium inclusions emit radiation that alters the original crystal structure. A glass-like material forms, with colors of red to brown, orange and yellow. Green is the rarest of the natural colors. Since the 1920s, most gemstones have undergone heat treatment to bring out their colors. This produces colorless zircons, as well as blue and golden stones.

Cut zircon stones from Vietnam. Image via Robert M. Lavinsky / Wikimedia Commons.

The creation of blue stones is in an interesting story relayed in “Gems and Crystals” by Anna S. Sofianides and George E. Harlow:

In the 1920s, a new blue gemstone suddenly appeared in the market. Endowed with spectacular brilliance, it was an immediate hit.

The creation of the blue zircon

The gems, it turned out, were zircons, normally brown to green, but never before blue. George F. Kunz, the legendary Tiffany gemologist, immediately suspected trickery; not only were there extraordinary stones available in abundance, but they were available all over the world! Upon Kunz’s behest, a colleague made inquiries during a trip to Siam (Thailand) and learned that a large deposit of unattractive brown zircon had stimulated color-improvement experimentation by local entrepreneurs. Heating in an oxygen-free environment made the drab material into “new” blue stones, which vendors sent to outlets worldwide. Even after finding out about the deception, the market simply accepted the information and the demand for the new gems continued unabated.

Among zircon customers, blue stones are a clear favorite. Red and green colors are also valuable. Colorless zircons are excellent imitators of diamonds, in appearance only, with a brilliant fire almost as dazzling as the real thing. However, zircon can be brittle and cutting takes great care. It breaks with a well-placed knock, due to internal stresses in the crystal caused by radiation damage and heat treatment. But it remains in demand for its stunning beauty. In addition, other factors that affect pricing of the gemstones are clarity and an absence of visible inclusions.

Zircon lore

Green zircon was among the stones of the Kalpa Tree of the Hindu religion, where it represented the tree’s foliage. This tree was a symbolic offering to the gods. Hindu poets of the 19th century described it as part of a glowing ensemble of precious stones that also included sapphires, diamonds and topaz.

The hyacinth and jacinth, reddish-brown and orange-red varieties of zircon, were a favorite stone of ancient Arabs, even mentioned in the famed “Arabian Nights.”

During the 14th century, zircon was popular as a safeguard against the Black Death, the great plague that wiped out a quarter of the population of Europe. People believed the stone possessed healing powers: to induce sleep, as an antidote against poison, and as an aid to digestion.

A rare olive-green zircon, measuring about 3.4 cm (1.3 inches) in length, from Myanmar. Image via Robert M. Lavinsky/ Wikimedia Commons.

December birthstone: tanzanite

A tanzanite crystal from the Merelani Hills, Arusha Region, Tanzania. Image via Parent Géry/ Wikimedia Commons.

Tanzanite is an unusual form of the mineral zoisite (calcium aluminium hydroxyl sorosilicate). Its colors, blue and violet, are due to the presence of vanadium in the zoisite crystals. This gemstone formed 585 million years ago under extreme heat during intense plate tectonic activity, in a place that would someday become Mount Kilimanjaro in northern Tanzania.

Today, you can only find tanzanite in the Merelani Hills near the foot of Mount Kilimanjaro.

Colors from different angles

In its natural form, tanzanite appears brown, yellowish green, blue and violet, flashing these colors when viewed from different angles. This phenomenon is pleochroism, where you can see different colors depending on how light hits the gemstone.

The type of lighting can also make a difference. Under fluorescent lights, tanzanite appears bluer, while under incandescent light, more violet hues emerge.

However, most crystals used in jewelry received doses of heat to remove the brownish color found in the natural tanzanite. The results are more intensely blue and violet gems. On rare occasions, heated stones can produce a green gem with secondary blue and violet colors. For cut gems, cutters can influence their overall color by how they craft the gem.

Tanzanite’s recent history

While most birthstones have histories spanning hundreds and even thousands of years, tanzanite’s story began in 1967. A Masai tribesman found unusual clear violet-blue crystals in the Merelani Hills in northern Tanzania. He notified a local tailor and prospector, Manuel d’Souza, who, upon finding the gemstones, filed the first of many mining claims.

Initially, d’Souza thought they were sapphires. But no one knew for sure. The stones made their way to geologists at the Gemological Institute of America where they identified them as an unusual form of zoisite.

And then, the famed jewelry purveyors, Tiffany & Company, took an interest in the gem. In 1968, they began a marketing campaign. To make the gems more appealing to buyers, they renamed blue zoisite to tanzanite, in honor of its country of origin. Finally, in 2002, the American Gem Trade Association selected tanzanite to join turquoise and zircon as December birthstones.

Beyond the December birthstone: birthstones for all months

January birthstone
February birthstone
March birthstone
April birthstone
May birthstone
June birthstone
July birthstone
August birthstone
September birthstone
October birthstone
November birthstone
December birthstone

Bottom line: As a matter of fact, December babies have three choices for their birthstone. Turquoise, zircon and tanzanite are the birthstones for December.
The post December birthstone: turquoise, zircon or tanzanite first appeared on EarthSky.

Achernar is the End of the River of Eridanus constellation

Editors of EarthSky — Wed, 22 Nov 2023 11:45:28 +0000

In a dark sky, you can see that Achernar marks the end of a great stream of stars known to the ancients as a celestial River. This is the constellation Eridanus the River, and Achernar is its brightest star. Chart via Chelynne Campion/ EarthSky.

Look for Achernar from southerly latitudes

The 9th-brightest star in all the heavens, Achernar, is well known to observers in the Southern Hemisphere. But many northern stargazers know this star by its name only. That’s because – although it shines at magnitude +0.45, making it one of our sky’s brightest stars – it’s extremely far south on the dome of stars surrounding Earth. If you’re north of about 33 degrees north latitude, Achernar never rises above your horizon at all. And yet this star remains one of the sky’s most famous stars as the star at the end of the River.

The River is – of course – the constellation Eridanus, which is large and easy to see in a dark-enough sky, even if you’re fairly far north on Earth’s globe. The northern part of this constellation is located near the extremely prominent constellation Orion the Hunter. Eridanus appears to swell up in a great loop near Orion, then meander southward. Finally – for most in the Northern Hemisphere – it drops out of sight below the southern horizon before it reaches its end.

But if you are far enough south – below 33 degrees north latitude – you’ll easily spot the River’s end as the bright star Achernar.

The 2024 lunar calendars are here! Best Christmas gifts in the universe! Check ’em out here.

A more detailed chart showing Achernar’s location in southernmost Eridanus, via Zwergelstern/ Wikimedia Commons (public domain).

How to see Achernar

For all practical purposes, you must be even further south – around 25 degrees north latitude – to see Achernar well. That is a line drawn around the entire globe passing through Miami in the U.S. and Taipei in Taiwan.

Nowhere in North America has it easy, seeing this star. For example, from Key West, Florida, Achernar rises only about 8 degrees above the southern horizon. Even farther south, from the southern tip of Hawaii’s Big Island, Achernar never quite makes it to 14 degrees.

And yet, if you are far-enough south, you can see Achernar easily. After all, this star is very bright!

Just as Achernar marks the end of the River, the River also has a beginning. The star Beta Eridani or Cursa, which itself is easily visible from the Northern Hemisphere, shines near Orion’s brightest star, Rigel.

It is visible from North America?

On most nights of the year, Achernar is not visible from anywhere in North America. However, around October 20 it skirts the southern horizon around midnight, never getting very high. Then as the months pass, it is visible earlier at night, around 10 p.m. in November, 8 p.m. in December and just after sunset in January. Being far to the south with no bright stars around it, Achernar stands out in its isolation. If you have a dark sky, and are far enough south, you’ll easily see Achernar’s constellation Eridanus making its loop under the constellation Orion.

@GEO101SUNY Here is a beautiful image of the meandering Owens River out in California!https://t.co/NbKG4o7GYt pic.twitter.com/XHawVHkoKr

— hayden (@haydenmhoyt) November 18, 2023

Earthly rivers are sometimes known for meandering. In the sky, the stars representing Eridanus the River – Achernar’s constellation – have a similar quality.

Achernar’s history and mythology

In fact, the name Achernar derives from an Arabic phrase meaning End of the River.

Interestingly, in early classical times the name Achernar was given to the star we now know as Theta Eridani, or Acamar. At that time Acamar was the brightest star of the constellation visible from Greece, and thus was considered the River’s end.

When voyagers discovered the brighter star farther to the south, it became Achernar, and the former Achernar became Acamar.

Apparently both names derive from the same phrase, “Al Ahir al Nahr,” according to Richard Hinckley Allen, whose 1899 book Star Names: Their Lore and Meaning is still the best around.

Science of Achernar

Data from the Hipparcos mission placed Achernar at about 144 light-years away. It is a B3V star, meaning that it belongs to the main sequence of stars. And, the B means the star is blue and it’s the bluest star among the top 10 brightest stars.

Achernar is much hotter and brighter than our sun. In fact, it’s estimated to be over 3,100 times the luminosity, of our sun. It’s about six times the mass of the sun.

Brighter, hotter (and bluer) than the sun, Achernar produces more energy in the non-visible ultraviolet (UV) wavelengths. When you take this into consideration, it pumps out some 3,000 to 5,000 times the solar energy level. The discrepancy is due to an uncertainty in the amount of UV radiation it produces.

Achernar is also a binary star system. The companion star – called Alpha Eridani B – is a white main sequence star with about two solar masses. It orbits the primary star at a distance of 12 astronomical units every 14 to 15 years.

Its rapid rotation results in a flattened star

As mentioned above, Achernar’s mass is about six times that of our sun, and its average diameter is nearly eight to 10 times that of the sun. But, while our sun spins on its axis once about every 25 days, Achernar completes one rotation in slightly more than two days, or nearly 15 times faster than our sun. This fast rotation produces an odd, flattened shape, first discovered by the European Southern Observatory’s Very Large Telescope (VLT) in 2003. Up close, Achernar would look more like a blue M&M, while our sun would look more like an orange. Read more about Achernar’s flattened shape from ESO.

This flattening of Achernar makes an exact surface temperature for this star hard to determine. The flattening causes the star’s poles to be hotter than the equator. Estimates range from about 14,500 to 19,300 kelvin (about 14,200 to 19,026 C or around 26,000 to 34,200 F).

In today's episode of fun space objects:

Archernar. The currently "least spherical" known star in the Milky Way, owning its shape to its rapid rotation.

Here it is compared in shape (and size) with our Sun. pic.twitter.com/CTXPckWsSs

— George Ioannidis (@Qupeplex) February 6, 2023

Achernar’s position is RA: 01h 37m 42.8s, dec: -57° 14′ 12″.

Bottom line: Achernar is the 9th brightest star and flattest star known. It marks the end of Eridanus the River. Here’s why much of Earth never sees it … and how you can.

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The post Achernar is the End of the River of Eridanus constellation first appeared on EarthSky.

Meet Hamal, an ancient equinox star

Editors of EarthSky — Sun, 19 Nov 2023 10:07:47 +0000

Most people see the constellation Aries the Ram as 3 stars in a compact grouping. The stars are Hamal (brightest), Sheratan and Mesarthim. Chart via Chelynne Campion/ EarthSky.

Start watching for Hamal in November

Hamal – also known as Alpha Arietis – shines as the brightest star in the constellation Aries the Ram. This star and two others – Sheratan and Mesarthim – make up the Head of the Ram. Aries is small. But the compact pattern of these three stars makes Aries relatively easy to find.

As seen from mid-northern latitudes, Hamal lights up the eastern sky on November evenings, will shine high in the southern sky by January evenings, and will sit low in the west by March evenings. This star is easily visible from Earth’s Southern Hemisphere, too. Try Stellarium to find Hamal’s height in your sky from your exact location on the globe.

As seen from the whole Earth, Hamal disappears from the night sky around April. It returns to the eastern sky before sunrise by about June, to begin another cycle of visibility.

The 2024 lunar calendars are here! Best Christmas gifts in the universe! Check ’em out here.

Aries finder charts

In 2023, bright Jupiter will lie in the dim constellation of Aries the Ram. So once you find Jupiter – and it’s easy to see right now in the evening sky – look for the 3 stars of Aries. Nearby you will find the open star cluster the Pleiades as well. Chart via EarthSky.

Bright Jupiter shines in the southeast in the constellation Aries after sunset in December 2023. Chart via EarthSky.

Constellation chart of Aries the Ram. Nowadays the sun passes in front of the constellation Aries from about April 19 to May 13. Image via IAU/ Wikimedia (CC BY 4.0).

Hamal was an equinox star

It’s fun to spot Hamal and its brother stars in the night sky. As an ancient equinox star, Hamal also has a profound significance in the history of astronomy.

In our modern era, if you could see the stars in daytime, you’d see the sun and Hamal in conjunction – lined up with one another, due north and south in right ascension – on or near April 24.

But, long ago, they were in conjunction exactly at the March equinox.

Nowadays, April 24 – the date of Hamal’s conjunction with the sun – is a little more than a month after the March equinox, which always takes place around March 20. This is the Northern Hemisphere’s spring equinox, and it’s a time of renewal throughout the northern half of Earth. So of course this time of year had significance to our ancestors, who were very much aware of their connection to the land and sky.

As the Earth orbits the sun, the sun appears to move across our sky, passing stars on the celestial sphere, including Hamal. In the past, the sun was in conjunction with Hamal at the March equinox. But no more. In our time, the sun is in front of the stars of Aries from April 18 until May 13. Image via John Goss.

Precession of the equinoxes

If you could backtrack some 2,500 years, you’d find the annual conjunction of the sun and Hamal happening on the March equinox. In fact, if you could backtrack 2,200 years, we’d also find the March equinox sun in conjunction with another star in Aries, Sheratan.

So you see that the location of the sun at the March equinox sun drifts in front of the stars. It moves westward in front of the backdrop constellations by about one degree (two sun diameters) every 72 years. This drifting is due to a well-known motion of Earth called precession, or sometimes the precession of the equinoxes.

The March equinox sun shone in front of the constellation Aries from about 2,000 to 100 BCE. At present, the sun shines in front of the constellation Pisces on the March equinox.

The 26,000-year cycle of precession. It’s caused by a wobble of Earth. Over this cycle, Earth’s northern axis can be imagined to trace out a circle on the celestial sphere. Therefore, precession causes Earth’s northern axis to point to different stars. Thus the identity of Earth’s pole star, or North Star, shifts over the cycle of 26,000 years. Image via Tfr000/ Wikimedia Commons (CC BY-SA 3.0).

First point of Aries

Even though the sun is no longer in front of Aries at the time of the March equinox, many people pay homage to the Ram and still refer to the March equinox point as the First Point of Aries.

This point on the celestial sphere – now in Pisces, due to precession – is one of the two points on the celestial sphere at which the celestial equator crosses the ecliptic. The other point – not as well known – is called the First Point of Libra (although it is now in Virgo), located exactly 180 degrees from it.

The First Point of Aries is considered to be the celestial “prime meridian” from which right ascension (like longitude in earthly coordinate systems) is calculated.

View larger. | The First Point of Aries is the point on the celestial equator at both the left and right extremes of this sky chart. The ecliptic (orange dotted sine curve) also passes through it. The First Point of Aries defines the ecliptic coordinate of 0 degrees longitude (or right ascension) and 0 degrees latitude (or declination). And note that the First Point of Aries is no longer in Aries. Now, due to precession, it’s in Pisces. Chart via Cmglee/ Timwi/ CC0/ NASA/ Wikimedia Commons (public domain).

Bottom line: The star Hamal is the brightest star in Aries the Ram. Thousands of years ago, the sun was in conjunction – or aligned north and south – with this star at the time of the March equinox.

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The post Meet Hamal, an ancient equinox star first appeared on EarthSky.