What is a day? You might casually talk about a day as a period of daylight. Or you could measure a day in relationship to the sun or the stars. Astronomers use the term solar day to describe a day relative to the sun. A solar day is the time from one solar noon – one local noon or high noon – to the next. It’s the interval between successive days as marked by the sun’s highest point in our sky. If you look at a day in that way, you can say that the longest days of the year come each year around the December solstice … no matter where you live on the globe.

Available now! 2024 EarthSky lunar calendar. A unique and beautiful poster-sized calendar showing phases of the moon every night of the year! And it makes a great gift.

The longest days are in December

What? Isn’t the shortest day for the Northern Hemisphere at the December solstice? Yes, it is, if we are talking about the period of daylight.

But, we’re talking about the (approximately) 24-hour interval from one solar noon to the next. In December, a day – one rotation of Earth relative to the noonday sun – is about half a minute longer than the average 24 hours, for the entire globe.

Keep in mind that the clocks on our walls don’t measure the true length of a day, as measured from solar noon to solar noon. To measure that sort of day, you’d need a sundial. A sundial will tell you the precise moment of local solar noon, when the sun reaches its highest point in the sky each day.

Days are always longer – as measured from one solar noon to the next – than 24 hours around the solstices, and less than 24 hours around the equinoxes.

Why are the days longer in December?

The days are at their longest now – for the entire globe – because we’re closer to the sun on the December solstice than we are at the June solstice. Earth’s perihelion – closest point to the sun – always comes in early January. So when we’re closest to the sun, our planet is moving a little faster than average in its orbit. That means our planet is traveling through space a little farther than average each day.

The result is that Earth has to rotate a little more on its axis for the sun to return to its noontime position. That effect lengthens the solar day by about eight seconds. In contrast, at aphelion, when the Earth is moving slower in its orbit, the solar day is about seven seconds shorter.

There’s another effect that happens during both the winter and summer solstices that increases the solar day by 21 seconds. It’s due to the way the sun moves mostly eastward, in relation to the stars, during solstices. Therefore, when the sun rises and moves up in the sky, it takes a bit longer to reach high noon from the previous day’s high noon.

For the winter solstice, the combined effects of these two phenomena increase the solar day by about 29 seconds.

Half a minute longer doesn’t sound like much, but the difference adds up. For instance, two weeks before the December solstice, noontime comes about seven minutes earlier by the clock than on the December solstice. And then two weeks after the December solstice, noon comes about seven minutes later by the clock than on the December solstice itself.

Sunrises and sunsets

Because the clock and sun are most out of sync right now, some befuddling phenomena cause people to scratch their heads at this time of the year. In the Northern Hemisphere, the year’s earliest sunsets precede the December winter solstice. And the year’s latest sunrises come after the December winter solstice. So the earliest sunsets came earlier in December for most of us; and the latest sunrises won’t come until early January.

In the Southern Hemisphere, the year’s earliest sunrises precede the December summer solstice, and the year’s latest sunsets come after the December summer solstice.

The fact that we’re closest to the sun in early January also means that Northern Hemisphere winter (Southern Hemisphere summer) is the shortest of the four seasons. Read more about the shortest season here.

However, at the same time … It’s the season of bountifully long solar days.

Visit Sunrise Sunset Calendars to find out the clock time for solar noon at your locality; remember to check the Solar noon box.

Bottom line: As measured from one solar noon to the next, December has the longest days – the longest interval from the sun’s highest point on one day to its highest point on the next day – for the entire Earth. And that’s true, no matter where you live on the globe.

A planisphere is virtually indispensable for beginning stargazers. Order your EarthSky Planisphere today!

The post Longest days accompany the December solstice first appeared on EarthSky.

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.

Available now! 2024 EarthSky lunar calendar. A unique and beautiful poster-sized calendar showing phases of the moon every night of the year. And it makes a great gift!

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.

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

Read More: Orion’s Belt and the Celestial Bridge

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.

Earliest sunset isn’t on the shortest day

Have you noticed your sunsets coming later now? That’s true for many of us, even though the December solstice is still more than a week away. For the mid-northern U.S. and similar latitudes – around 40 degrees north latitude – the earliest sunsets of the year came around December 8. That would be the latitude of New York City; Philadelphia, Pennsylvania; Kansas City, Missouri; Denver, Colorado; Reno, Nevada; Beijing, China; Madrid, Spain; and Naples, Italy.

For more southerly latitudes – say around 30 degrees north latitude – the earliest sunsets of the year came in late November and early December.

And what about the Southern Hemisphere? At this same time, the year’s earliest sunrises have happened or are happening, as you progress toward your longest day at the December solstice.

Then, closer to the Arctic and Antarctic Circles, the earliest sunset and earliest sunrise happen nearer the solstice.

Want to know the date of your earliest sunset (or sunrise)? Sunrise-sunset.org provides the sunrise/sunset times to the second for locations around the globe.

The exact date of the Northern Hemisphere’s earliest sunset and the Southern Hemisphere’s earliest sunrise varies by latitude.

But at temperate latitudes, both of these annual hallmarks in our sky come a few to several weeks before the December solstice, not at the solstice as you might expect.

Available now! 2024 EarthSky lunar calendar. A unique and beautiful poster-sized calendar showing phases of the moon every night of the year! And it makes a great gift.

Why?

The next solstice in 2023 comes at 3:27 UTC on December 22 and marks an unofficial beginning for winter in the Northern Hemisphere. So for the Northern Hemisphere, this upcoming solstice brings the shortest day and longest night of the year. Then why isn’t the earliest sunset on the year’s shortest day?

Basically, it’s because of the discrepancy between the clock and the sun. A clock ticks off exactly 24 hours from one noon to the next. But an actual day – as measured by the spin of the Earth, from what is called one solar noon to the next – rarely equals 24 hours exactly.

Also, solar noon is simply called midday, because it refers to that instant when the sun reaches its highest point for the day. Thus, in the month of December, the time period from one solar noon to the next is actually half a minute longer than 24 hours. For example, in Philadelphia, Pennsylvania on December 7 the sun reaches its noontime position at 11:52 a.m. local standard time. Then, two weeks later – on the winter solstice – the sun will reach its noontime position around 11:58 a.m. So that’s six minutes later than on December 7.

Visit Sunrise Sunset Calendars to know the clock time for sunrise, solar noon and sunset plus day length in your part of the world, remembering to check the solar noon and day length boxes.

Another key point is that the later clock time for solar noon means a later clock time for sunrise and sunset. This can be seen in the table below.

For Philadelphia, Pennsylvania

Latest sunrise and earliest sunset aren’t on the solstice

As you might have guessed, the latest sunrises aren’t on the day of the solstice either. For middle latitudes in the Northern Hemisphere, the latest sunrises come in early January.

Although there’s variation in the exact dates, the sequence is always the same for both hemispheres. First, earliest sunset before the winter solstice, the winter solstice itself, latest sunrise after the winter solstice. Then, half a year later, earliest sunrise before the summer solstice, the summer solstice itself, latest sunset.

So by all means, check out the earliest and latest sunsets and sunrises in your area. They are always lovely and happen around every solstice.

Sunsets from the EarthSky Community

Bottom line: The solstice comes on December 22, 2023, at 3:27 UTC. Does that coincide with the earliest sunsets? It depends on where you live. The earliest sunsets at mid-northern latitudes happen weeks before the solstice. By comparison, latitudes closer to the equator have their earliest sunsets in late November, or earlier in December. And then latitudes closer to the Arctic Circle will have their earliest sunsets closer to the December solstice.

Solstice tale of two cities: New York, New York, and St. Augustine, Florida

EarthSky’s monthly night sky guide: Visible planets and more

The post The earliest sunset comes before the winter solstice first appeared on EarthSky.

Check out these Comet Nishimura photos from around the world.

Nishimura and the Sigma-Hydrid meteors

Comet C/2023 P1 (Nishimura) burst into our consciousness in August of 2023. It never got as bright as some hoped, but it still made a glorious target for astrophotographers. But is there still a chance to see parts of Comet Nishimura? Yes, only not as the comet itself, but instead as the dust it left behind in our atmosphere. Astronomers think Nishimura may be the parent comet of an annual meteor shower known as the Sigma-Hydrids. This minor annual shower is active each year between December 9 and 12. Scientists will be closely monitoring the shower this year to see if there’s an uptick in meteors. And it might be worth it for us to go out and look, too!

So, if Nishimura is indeed related to the Sigma-Hydrids, then the comet might have “refilled” its path with icy comet particles. While this is normally a very quiet shower, it might be more active this year.

The video below is from December 2022, taken in the Caribbean. It’s a Sigma-Hydrid meteor, a possible Nishimura-related meteor!

Videos of Nishimura

Professional observatories that peer at the sun have caught the comet in their images. You’ll find some amazing videos of the comet below.

Comet Nishimura – that great icy ball moving through space, which so many have captured on film – was closest to Earth on September 12. It was then closest to the sun (perihelion) on September 17.

Meanwhile, the comet is also expected to reappear in our dawn skies toward the end of 2023. But by then it’ll be too distant, and too dim, to view, as it sweeps farther away. But we may get to see some of what it left behind in December, however, with the Sigma-Hydrids meteor shower!

Wondering what happened to comet Nishimura? It's still quite happily sunbathing in the field of view of our @USNRL HI-1 camera on @NASA STEREO-A! Lots of great ion tail / solar wind interaction happening! ????

Download the full-res movie here: https://t.co/gkv2HCpIUS pic.twitter.com/xzHvdgBfjt

— Karl Battams (@SungrazerComets) September 26, 2023

The story of comet Nishimura

Hideo Nishimura of Kakegawa, Japan, was photographing the night sky on August 11 and 12, 2023, when he captured a new comet that now bears his name: comet C/2023 P1 (Nishimura). In fact, the comet was hiding in the sun’s glare before Nishimura picked it up in his images.

It continued to brighten as it closed in on the sun (perihelion was September 17). Later, after passing closest to Earth on September 12, it emerged low in the evening sky. Some saw it with binoculars in the western evening twilight.

A local comet

On September 1, 2023, NASA/ JPL made new orbital calculations that indicated that comet Nishimura orbits the sun every 435 years, which suggests this is a “local comet” from our solar system and not an interstellar comet.

Closest approach to Earth occurred on September 12, 2023, when the comet passed 78 million miles (125 million km) from Earth.

Perihelion – or closest approach to the sun – was on September 17, 2023, at 27 million miles (43 million km) from our star.

In fact, during perihelion, comet Nishimura passed closer to the sun than Mercury’s orbit.

Sightings of comet Nishimura

Comet Nishimura (C/2023 P1) on Sept 5, 2023. For this single shot I used my A7s and a 135mm lens.

Nishimura is a new comet that was discovered on August 11, 2023. It's expected to brighten to a magnitude of 1.8. Its closest approach to us will be on Sep 12 and its perihelion on… pic.twitter.com/BXhDo0IOpq

— Dr. Sebastian Voltmer (@SeVoSpace) September 6, 2023

comet C/2023 P1 (Nishimura) from Belfast, N Ireland at around 5am on 4th Sept 2023. Cropped from a 100mm image – stack of 50 x 3secs at ISO800. (Some problems with stacking caused a halo above neighbour's roof!) @martinastro2005 pic.twitter.com/jCuuZa3egN

— Philip?EcotrakNI (@EcotrakNI) September 4, 2023

comet C/2023 P1 (Nishimura): Such a strong solar wind. The disconnection event on September 2nd – the spectacular development in a 20-minute animation (RASA 11 QHY600) and 4x80sec red Michael Jäger pic.twitter.com/qf43YqhBbl

— Michael Jäger (@Komet123Jager) September 2, 2023

Bottom line: Comet Nishimura may be the parent comet to the Signma-Hydrid meteor shower, which peaks between December 9 and 12. Will the shower be more active this year? The only way to know is to go look!

See photos of comet Nishimura from the EarthSky community

Via:

NASA

Harvard

IAU Minor Planet Center

Star Walk

The post Comet Nishimura and the Sigma-Hydrid meteors first appeared on 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?

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

Finder charts for Northern Hemisphere evenings

Finder charts for November Southern Hemisphere evenings

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

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.

More Mercury elongation comparisons for 2023

Mercury photos from our community

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.

Look for Mintaka in Orion’s Belt

See the three stars at Orion the Hunter’s midsection? These stars are Alnitak, Alnilam and Mintaka. In fact, they’re very noticeable and famous in many cultures as Orion’s Belt. In the Southern Hemisphere, the Aymara people of Bolivia, Peru and Chile saw the Belt as a celestial bridge or a staircase to the world of souls. But astronomers see the Belt as a type of bridge, too. These stars link the sky’s northern and southern hemispheres.

Consider Mintaka, which is the Belt’s westernmost star. It sits almost directly astride the celestial equator: the projection of Earth’s equator onto the stellar sphere.

So where can you find Mintaka and the constellation Orion? In late November, from around the world, Orion rises in your eastern sky around 9 p.m. and climbs highest for the night around 1 to 2 a.m. local time.

When dawn is breaking, or about to break, say around 5 to 6 a.m., the Hunter sits low in your western sky.

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

Mintaka shines on the celestial equator

Mintaka’s location on the celestial equator makes it a good guidepost for finding directions here on Earth. That is, Mintaka and the other stars of the Celestial Bridge are visible worldwide. From all over the world, Mintaka rises due east, sets due west, and remains in the sky for 12 hours. It climbs to its highest point in the sky midway between rising and setting.

When it’s highest in the sky, if this star shines at your zenith (your straight-overhead point), then you must be at the equator.

If this star shines in the southern half of your sky, then you must be north of the equator.

If this star shines in the northern half of your sky, then you must be south of the equator.

The story of the Celestial Bridge is one of many about the constellation Orion. That’s because it’s so noticeable on our sky’s dome. So watch for it when you’re outside one evening soon!

Bottom line: The indigenous Aymara people of the Andes and Altiplano regions of South America see the famous sky feature we know as Orion’s Belt as a celestial bridge between the sky’s Northern and Southern Hemispheres. In fact, its westernmost star, Mintaka, lies directly on the celestial equator.

The post See Orion’s Belt as a celestial bridge between hemispheres first appeared on EarthSky.

Sometimes we get notes from people in Australia and New Zealand – who are across the International Date Line – that they wish we’d provide our charts a day earlier. This chart is for you!

Via Guy Ottewell’s blog. Re-printed with permission. Edits by EarthSky.

There’ll be a pretty gathering of three objects low in the west after sunset on November 15, 2023. But the meetup is more likely to be seen from Earth’s Southern Hemisphere. As the young moon – a waxing crescent in the evening sky – climbs away from the sun, it’ll pass close to Mercury and the red star Antares.

Why Southern Hemisphere? Don’t we all see the same sky? We do, to a large extent. But our orientation – from our various parts of Earth – gives us a varying perspective on the sky. And – for all of us around the globe right now – the moon, Antares and Mercury are now low in the evening sky, in the west only shortly after sunset. From the Southern Hemisphere now, the ecliptic (pathway of the sun, moon and planets) makes a reasonably steep angle with the western evening horizon, placing the trio above the sunset. But the moon, Mercury and Antares are all on a part of the ecliptic that slopes south from where the sun now is. And this fact depresses the view still more for Northern Hemisphere observers.

So our scene this time is drawn for a location that approximates Australia and New Zealand.

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

The moment when this trio of bright bodies is tightest – fitting within a circle of diameter just over 4 degrees – is at 21 UTC on November 14. But they are then still so low in the western sky, only about 17 degrees from the sun, that the following evening probably gives a better chance of spotting them.

What’s more, on November 15, the crescent of the moon will be slightly thicker and easier to see. Good luck spotting this pretty sky scene.

Bottom line: A tight grouping of the waxing crescent moon, planet Mercury and red star Antares appears in this chart showing the trio as seen from Australia and New Zealand on the evening of November 15, 2023. Be sure to look as soon as possible after sunset!

The post Sky trio for you, Southern Hemisphere friends first appeared on EarthSky.

Orion the Hunter’s season in the sky

November evenings are a great time to say hello to everyone’s favorite constellation: Orion the Hunter. Find Orion now and enjoy it for months to come! Without a doubt, Orion is the easiest-to-identify of all constellations. Look for it in the eastern sky this month, say, between the hours of 10 p.m. and midnight (that’s your local time, the time on your clock no matter where you are). You’ll notice Orion’s Belt first. The Belt is made of three stars in a short, straight row. The Belt stars aren’t the brightest in the sky. But they’re the reason Orion will catch your eye.

And you’ll also notice Orion’s two brightest stars – Betelgeuse and Rigel – shining on opposite sides of the Belt.

You can find this constellation easily. You can point it out to your friends!

So look for Orion. It’s at this time of year – say, around mid-November and into early December – that casual skywatchers start to notice Orion and comment on it.

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

As the weeks pass …

In mid-November, Orion doesn’t reach its highest point until an hour or two after midnight your local time. Northern Hemisphere skywatchers will find it high in the south at its highest point. Southern Hemisphere skywatchers will find it generally northward.

Like all the stars, Orion’s stars rise some four minutes earlier with each passing day, or about two hours earlier with each passing month. If you see Orion shining in the east at 10 p.m. tonight, look for this constellation to be in the same place in the sky at about 8 p.m. a month from now. Or if Orion is due south at 2 a.m. tomorrow, look for Orion to be due south at midnight one month later.

This shift in Orion’s location is due to Earth’s movement in orbit around the sun. As we move around the sun, our perspective on the stars surrounding us shifts. At the same hour daily, all the stars in the eastern half of the sky climb up a bit higher. And at the same time on your clock each day, all the stars in the western half of the sky sink a bit closer to the western horizon.

Star map of Orion

Bottom line: By mid-to-late November, the famous constellation Orion the Hunter is back in the evening sky! Its most recognizable feature is called Orion’s Belt: a short, straight line of three medium-bright stars.

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The post Orion the Hunter is back in the evening sky first appeared on EarthSky.

The Summer Triangle and its 3 stars

The Summer Triangle is the signature star formation in the Northern Hemisphere’s summer sky. However, as the September equinox comes and goes – and as the weeks of autumn begin to slide by – you’ll still notice this famous trio of stars. So, look for the Summer Triangle after dark in early November. It will actually continue to shine after dark in November and December, and is even visible still in January. Look for it tonight in the early evening, high in your western sky.

By the way, the Summer Triangle isn’t a constellation. It’s an asterism, or an obvious pattern or group of stars with a popular name. In fact, the Summer Triangle consists of three bright stars in three separate constellations. The bright star Vega is in Lyra the Harp. Deneb is in Cygnus the Swan. And Altair is in Aquila the Eagle.

In the month of June – around the June solstice – the Summer Triangle pops out in the east as darkness falls and shines all night long. But now – after sunset in November – the Summer Triangle appears high in the western evening sky. As evening deepens, the Summer Triangle descends westward, with all three of its stars staying above the horizon until mid-to-late evening.

Altair – the Summer Triangle’s southernmost star – will set around 10 to 11 p.m. tonight at mid-northern latitudes. Notice where you see the Summer Triangle at a given time this evening. The Summer Triangle will return to this same place in the sky some four minutes earlier with each passing day, or two hours earlier with each passing month.

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

Look for Orion, too

Then as the Summer Triangle sinks close to the western horizon around mid-evening, turn around to see Orion the Hunter – the signpost constellation of winter – rising in the east.

Bottom line: Look westward this evening for the three brilliant stars of the humongous Summer Triangle: Vega, Deneb and Altair. In fact, you can still see the Summer Triangle through January.

EarthSky astronomy kits are perfect for beginners. Order yours from the EarthSky store.

The post See the Summer Triangle in northern autumn first appeared on EarthSky.

Watch for the brightest star, Sirius

The planet Venus is up at dawn now. And it’s very bright, much brighter than any other planet or star. But – at this time of year – we always get questions about another bright object in the dawn sky. Andy wrote:

Early this morning, looking south, I saw a beautiful star, bright and multicolored … Can you identify it for me?

And Paula wrote:

This morning two of us got up early. We found a pulsing star straight down the sky below Orion’s Belt. It was pulsing the colors of green, yellow, blue and red like a strobe light. I will search for it every morning as it was so enchanting.

If you’re up before daybreak on these October mornings, take a moment to see this star, which is the sky’s brightest star, Sirius. This star is so brilliant that you can even see it from a light-polluted city. And you can see it if you stay up late, too! It’s rising in the middle of the night now, as seen from around the globe, and is high in the sky – at its best – by dawn.

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What is that bright twinkling star?

This star is enchanting, so much so that – every year, beginning in Northern Hemisphere autumn – we get many, many questions about a multicolored star twinkling in the southeastern to southern sky after midnight. This star typically turns out to be Sirius, which is in the constellation Canis Major the Greater Dog and is sometimes called the Dog Star.

Why does Sirius twinkle so much?

Sirius appears to flash different colors when it’s low in the sky. Really, all the stars are flashing different colors, because light is composed of all the colors of a rainbow, and the journey through our atmosphere breaks starlight into its component colors via refraction. But you don’t notice the colors of the other stars much, because they’re not as bright as Sirius, which is the brightest star visible from anywhere on Earth.

Since our atmosphere is causing the light to break into its colors, and since Sirius is often seen low in the sky now (where you are peering at it through a thicker layer of atmosphere than when it’s overhead), the flashing colors of Sirius are very obvious. When Sirius is higher in the sky – which it is close to dawn in the month of October – or in the evening sky in January and February – you’ll find that Sirius shines with a steadier, whiter light.

So, on these October mornings, watch as Sirius winks at you in the wee hours before dawn!

Bottom line: We get many questions about a bright, colorful, twinkling star on these October mornings. It’s the star Sirius in the constellation Canis Major, and the brightest star in the sky. Plus, you’ll know it’s Sirius, because Orion’s Belt always points to it.

Read more: Flashing star in autumn? Here are 3 candidates

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The post Brightest star, Sirius, high on October mornings first appeared on EarthSky.