Latest solar noon comes in February

For you, if you’re time-conscious … the days around February 11 mark the latest solar noon for all of 2024, and for the entire globe, by the clock. However, solar noon isn’t a clock event, even though our clocks and calendars measure its continual shift throughout the year. So what is it? It’s a natural event. Solar noon – aka midday – refers to that passing instant when the sun reaches its highest point for the day, midway between sunrise and sunset.

At solar noon, the sun is said to cross your meridian, as depicted on the diagram below. No matter where you live worldwide, the sun can only be at one of three places in your sky at solar noon: at your zenith (straight overhead), south of zenith, or north of zenith. The noonday sun can only reach zenith in the tropics. From northern temperate latitudes, the noonday sun is always south of zenith. At southern temperate latitudes, the noonday sun is always north of zenith.

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The equation of time

We invite you to check out the graph below. It shows what’s called the equation of time. That’s a fancy name for the discrepancy between solar noon and clock noon. As the graph shows, the latest solar noon in February occurs a solid 1/2 hour later by the clock than the year’s earliest solar noon in early November.

Yearly, the latest solar noon happens on (or near) February 11 and the earliest solar noon happens on (or near) November 3. That’s true no matter where you live worldwide. North, south, east, west on the globe … it doesn’t matter. For all of us, solar noon happens over 30 minutes later by the clock on February 11 than it does on November 3.

Before the advent of time zones and standard time, the equation of time graph (below) applied to anywhere worldwide. In our day and age, the graph refers to places that reside on the center line of a given time zone. For example, Denver, Colorado – at 105 degrees west longitude – sits on the center line of the Mountain Standard Time zone. So, in Denver, solar noon reads 12:14 p.m. by the clock on February 11, and 11:43 a.m. by the clock on November 3.

Elsewhere within a given time zone, the standard clock time for solar noon differs. Keep reading to understand why.

Where are you in your time zone?

Earth is divided into around 24 time zones, and each time zone is (in theory) 15 degrees of longitude wide. Because Earth is a sphere, time zones are widest across at the equator. They reduce in width as you go north or south, until they reach to zero degrees at the poles. In other words, the time zones meet at the poles. So, at the equator, a time zone is (in theory) about 1,035 miles (1,665 km) wide. By the way, we keep saying “in theory” because time zone borders typically aren’t straight lines. They’re often drawn in a zigzag fashion to accommodate the boundaries of nations, states or provinces.

But for all of us – unless you live at Earth’s North or South Pole – your time zone has some width to it. And you might have noticed that sunrise and sunset in the sky happen later (by the clock) as you go directly west in a given time zone.

So it is for solar noon. Solar noon comes 4 minutes later by the clock for every 1 degree you live west of your time zone’s eastern edge. Solar noon comes 4 minutes earlier by the clock for every 1 degree you live east of your time zone’s western edge. No matter. It’s still the case that – in any year, and at any location – solar noon happens 1/2 hour later by the clock on February 11 than on November 3.

Based on standard time

By the way, we emphasize we’re talking about standard time. We are not talking about daylight saving time or summer time, in which we pretend that it’s one hour later than it is.

But there’s no need to go through mental gymnastics to figure out the clock time for solar noon in your location. Simply visit the Sunrise Sunset calendar site, enter your location, and look at the column marked solar noon.

In this way, you’ll know your clock time for solar noon for any day of the year.

Unequal length of solar days

The day – as measured from one solar noon to the next – rarely equals 24 hours. In fact, a 24-hour solar day happens only four times a year, on or near these dates: February 11, May 14, July 26 and November 3. Again, we invite you to study the equation of time graph above. The 24-hour solar days only take place at the turning points above (February 11 and July 26) and below (May 14 and November 3).

The sun and the clock only agree four times a year: on or near April 15, June 15, September 1 and December 25. Look at the graph above and you can see that the solar day is shorter than 24 hours on April 15 and September 1, yet longer than 24 hours on June 15 and December 25.

Shorter days at equinoxes, longer days at solstices

Earth-sun geometry dictates seasonal variation in the length of solar days. Solar days are less than 24 hours long for roughly 3 months centered around the equinoxes (March 20 and September 23). And solar days are longer than 24 hours for roughly 3 months centered around the solstices (June 21 and December 21).

Two reasons account for the unequal length of the solar day. First and foremost, the tilt of the Earth’s axis causes the solar day to be more than 24 hours long around the solstices, and less than 24 hours long around the equinoxes. But Earth’s eccentric orbit plays a role, too, either accentuating or lessening the length of the solar day.

Around the December solstice, the Earth is some 3 million miles (5 million km) closer to the sun than on the June solstice. So Earth travels most swiftly in its orbit for the year in December and January. It travels most slowly in June and July.

Hence, at and around the December solstice, the Earth must rotate farthest on its axis for the sun to return to its noontime position. That gives us the year’s longest solar days around the December solstice: 24 hours + 30 seconds.

In contrast, the solar days accompanying the June solstice are considerably shorter: 24 hours + 13 seconds.

Mean sun versus real sun

In short, the mean sun used by the clock is a fiction. The clock presumes Earth’s rotational axis stands upright as we revolve around the sun. The clock also presumes Earth goes around the sun in a perfect circle. Neither presumption is correct. Earth’s rotational axis is titled nearly 23.5 degrees out of perpendicular to its orbital plane. And, as mentioned before, Earth’s distance from the sun varies by about 3 million miles (5 million km).

The mean solar day is 24 hours long. But the real solar day (as measured by the sundial) varies in length throughout the year. The discrepancy between the clock and the sundial is never greater than 1/2 minute on any given day. Even so, the discrepancy accumulates daily for roughly three months. That’s why the latest solar noon in February comes 1/2 hour later by the clock than the earliest solar noon in early November.

Want to know the time difference between the clock and sundial for any day of the year? Go to this online calculator and scroll down to the equation of time column (first column). Additionally, you can find out the solar day duration under the fifth column.

Zero shadow day

For those living between the Tropic of Cancer and Tropic of Capricorn, twice a year, you’ll have a zero shadow day. That’s when – from your location – the declination of the sun is equal to your latitude. So when that happens, the sun crosses your local meridian at your zenith – the point directly overhead – and does not cast a shadow. Of course, the date this occurs varies by location.

For example, the people of Bengaluru, India, celebrate zero shadow day every year on April 25 and August 18.

Bottom line: February 11 ushers in the latest noontime sun of the year by nature’s clock. And for folks living at the Earth’s equator, this date also marks the day of the year’s latest sunrise and latest sunset.

The post Year’s latest solar noon happens on February 11 first appeared on EarthSky.

Mizar and Alcor

Mizar and its fainter companion star Alcor make up one of the most famous double stars in the sky. These two stars are bound to one another by gravity. And they’re located in the famous Big Dipper, an asterism which is ascending in the northeast on February and March evenings. You can spot this pair easily, and it’s lots of fun to see them! Look at the middle star in the Dipper’s handle. You’ll spot Mizar first, because it’s brighter. Look closely, and you’ll see fainter Alcor right next to Mizar.

Historically, Mizar and Alcor are a test of eyesight. But even people with less-than-perfect eyesight can see the two stars, especially if they’re looking in a dark, clear sky. This pair of stars in the Big Dipper’s handle has the nickname of horse and rider. If you can’t see fainter Alcor with the unaided eye, use binoculars to see Mizar’s nearby companion.

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Mizar alone is a quadruple star

Mizar is perhaps the Big Dipper’s most famous star, glorified in the annals of astronomy many times over. Apart from Alcor, Mizar by itself is a double star. In fact, it was the first double star known. An Italian astronomer brought it to the attention of Galileo in 1617. A third Italian astronomer, Giovanni Battista Riccioli, wrote about Mizar as a double star.

Few, if any, astronomers back then even dreamed that double stars were anything other than chance alignments of physically unrelated stars. Yet, in 1889, a spectroscope revealed that the brighter component of Mizar’s two stars consisted of two stars itself. This made Mizar the first binary star ever discovered by spectroscopic means.

Later, Mizar’s dimmer telescopic component also showed itself to be a spectroscopic binary, meaning that Mizar consists of two sets of binaries, making it a quadruple star.

And Alcor is double

As for Alcor, scientists long believed that Mizar and Alcor were not gravitationally bound and did not form a true binary star system. Not until 2009 did our knowledge expand. Two groups of astronomers independently reported that Alcor is itself a binary, consisting of Alcor A and Alcor B. Astronomers now believe that the Alcor binary system is gravitationally bound to the Mizar quadruple system. That makes this “double” star six stars in all, but we can only see two with the unaided eye.

Mizar and Alcor have proven to not only be a test of human eyesight, but a test of the limits of our technological vision as well.

Bottom line: Famous star pair Mizar and Alcor is easy to find in the handle of the Big Dipper. Mizar is really four stars, and Alcor is two stars. So what we see as two stars are really six in one!

The post Mizar and Alcor in the bend of the Big Dipper first appeared on EarthSky.

3-point summary

ChatGPT and Deborah Byrd created this 3-point summary of the article below:

• The April 8, 2024, eclipse is part of Saros 139, which began in the year 1501 and will conclude in the year 2763.
• Saros 139 includes a total of 71 related eclipses, with the April 8 eclipse being the 30th within this series.
• Related eclipses in a single S

  aros Cycle trace similar paths across Earth’s globe. But the eclipse path – as traced by the moon’s shadow – falls at a different place on the globe for each eclipse.

Saros, the much-revered eclipse cycle

The next total solar eclipse is two months from today! Whether you intend to watch the partial, or the total eclipse, make your viewing plan now. It might seem as if eclipses happen randomly. But this coming eclipse – and every eclipse – is part of a pattern, or Saros Cycle. The April 8 eclipse belongs to Saros 139.

Saros 139 started in the year 1501. It’ll end in the year 2763. This particular saros contains 71 related eclipses. The April 8, 2024, eclipse is the 30th of these 71. What makes these eclipses related? They trace a similar pattern across the globe, albeit not in the exact same spot on the globe.

The saros is probably the most famous of the many, many eclipse cycles.

Chaldean (neo-Babylonian) astronomers left the earliest-discovered historical records of what is known today as the saros. Their records came from the last several centuries BC.

Saros period equals 18.03 years

For eclipse aficionados, the saros is useful because it organizes eclipses into families. Each saros series typically lasts 12 to 13 centuries and contains 70 or more eclipses.

Eclipses within a solar Saros series recur after 223 lunations, that is, 223 returns to new moon. And the time between new moons is 29.530589 days. So, the Saros period very nearly equals 6,585 1/3 days. That’s 18 years, plus 10, 11 or 12 (and a third) days, depending on the intervening number of leap years.

And so the immediate forerunner to the April 8, 2024 – its brother eclipse in the saros cycle – came to pass 18 years and 10 1/3 days before this coming April 8. That earlier eclipse happened on March 29, 2006. Looking ahead, the next eclipse belonging to Saros 139 – a future brother eclipse in this saros – will be in 18 years and 11 1/3 days. It’ll happen on April 20, 2042).

If you look at maps of all three eclipses (2006, 2024 and 2042), you’ll see what we said above is true. They all trace a similar path across the globe, albeit not in the exact same spot on the globe. See diagrams below.

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Saros begins at one pole and ends at the other

Every saros series begins with a number of partial eclipses near one of Earth’s polar regions.

And so it was with Saros 139. Its first eclipse appeared in a far-northern part of the globe on May 17, 1501. Some 1,262 years later, the final eclipse of Saros 139 will take place along the coast of Antarctica on July 3, 2763.

Some Saros series begin at Earth’s North Pole, and others at Earth’s South Pole. Why?

The Earth’s orbit around the sun – and the moon’s orbit around Earth – aren’t on the same exact plane. The moon’s orbital plane is titled to that of Earth by about 5 degrees. The points where the moon’s orbit intersect the Earth’s orbit are called nodes. There’s an ascending node, where the moon is ascending through Earth’s orbital plane. And there’s a descending node, where the moon is passing from above the plane to below it.

The new moon must be at a node in order for a solar eclipse to take place. Otherwise, the moon can’t come between us and the sun.

And there lies the trick to where a saros series begins on Earth. Any saros series that starts at the moon’s ascending node starts near the North Pole and ends near the South Pole. Conversely, any saros series coinciding with the moon’s descending node starts in the south polar regions and ends north.

Saros 139 – containing the April 8, 2024, eclipse – started at an ascending node, and therefore at the North Pole.

Some eclipses in the series are partial

The early and late stages of any solar saros cycle present a rather poor alignment between the new moon and sun.

For this reason, the first seven eclipses and last nine solar eclipses of Saros 139 are only partial eclipses.

In short, no central solar eclipses – total, annular or hybrid – happen in the beginning and ending stages of any saros.

For Saros 139, the moon’s dark umbral shadow first landed on Earth and totally eclipsed the sun (though extremely briefly) on August 11, 1627. Since then, the central duration of these eclipses has been getting progressively longer.

April 8 eclipse: Saros 139’s longest solar eclipse to date

The eclipse on April 8, 2024, will present the longest total solar eclipse of the series to date (central duration: 4 minutes, 28 seconds). In comparison, the previous total solar eclipse on March 29, 2006, was somewhat shorter (central duration: four minutes, seven seconds). The next one on April 20, 2042, will be somewhat longer (central duration: four minutes, 51 seconds).

Longest totality yet to come

For the next 162 years, each following eclipse in this series will feature a longer total solar eclipse than its predecessor. Nine saros periods from now – July 16, 2186 – will showcase the longest total solar eclipse of Saros 139.

That’s not all, however! With a central duration of seven minutes and 29 seconds, it’ll present the longest total solar eclipse within a period of 10,000 years (4000 BCE to 6000 CE).

Convergence of factors for a long eclipse

Any total solar eclipse lasting seven minutes or longer is lengthy to the extreme. Indeed, a “perfect storm” of factors is necessary for a seven-minute total eclipse of the sun to take place:

The sun needs to be at or near apogee (farthest from Earth)
The moon needs to be at or near perigee (closest to Earth)
The greatest eclipse must happen in the tropics, rather close to the equator

Saros 139 can boast that five of its 43 total eclipses last over seven minutes. Although 40 solar saros series are in play at any one time, Saros 139 is head and shoulders above the rest for staging long totalities. In fact, this is the one and only solar saros series to provide seven-minute eclipses in the five-century period from 2001 to 2500:

2150 June 25 (seven minutes, 14 seconds)
2168 July 05 (seven minutes, 26 seconds)
2186 July 16 (seven minutes, 29 seconds)
2204 July 27 (seven minutes, 22 seconds)
2222 Aug 08 (seven minutes, 6 seconds)

Another total solar eclipse lasting seven minutes or better won’t happen again until June 14, 2504. After that – until 6000 CE – no solar saros will duplicate Saros 139’s feat of five seven-minute total solar eclipses.

The last time a solar saros produced five seven-minute total eclipses was 1,823 years previous to solar Saros 139. Saros 81 performed the trick from the years 327 to 399:

327 June 6 (seven minutes, 3 seconds)
345 June 16 (seven minutes, 17 seconds)
353 June 27 (seven minutes, 24 seconds)
381 July 08 (seven minutes, 22 seconds)
399 July 19 (seven minutes, 2 seconds)

The April 8 eclipse is the 30th of 71 members making up the grand succession of the Saros 139 solar eclipses.

Three times a charm: triple saros

Oftentimes, a given eclipse cycle is actually a combination of eclipse cycles. The saros eclipse cycle of 223 lunations stands as no exception. For example, the Tzolkinex Cycle with a period of 88 lunations and Tritos Cycle with a period of 135 lunations nicely add up to one saros period of 223 lunations.

Moreover, three saros periods add up to one exeligmos period of 669 lunations. The exeligmos has the advantage of sporting an integral number of days: 19,756 days (54 years and 33 days).

The longest solar eclipse of Saros 139 will come exactly three exeligmos periods after the April 8, 2024, total solar eclipse. That’s in 162 years and 99 days, on July 16, 2186.

Bottom line: Enjoy the April 8 eclipse as you witness the 30th of 71 member eclipses in the illustrious procession known as Saros 139.

The post The April 8 eclipse is part of Saros 139. What does that mean? first appeared on EarthSky.

Taurus the Bull

The constellation Taurus the Bull is visible during the fall through spring in the Northern Hemisphere (or spring through fall in the Southern Hemisphere). It sits in the evening sky close to the easy-to-see constellation Orion.

Basically, Taurus the Bull takes the shape of a two-pronged fork, with the center V-shape consisting of an actual star cluster – a family of stars in space – that we call the Hyades. The Hyades marks the face of the Bull. The bright red star Aldebaran shines in the V and represents the Bull’s fiery eye. In addition, Taurus holds another famous star cluster, which we call the Pleiades or Seven Sisters. You’ll notice it has the shape of a tiny dipper.

Moreover, Taurus is also the radiant point for the annual Taurid meteor shower, which happens every year in November.

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Locating Taurus the Bull

Taurus is a constellation of the zodiac, which means the sun, moon and planets travel through it regularly. In fact, the sun passes through the constellation Taurus from about May 14 to June 21. However, you can’t see Taurus when the sun is within its borders.

Generally speaking, Taurus is easy to find on its own. That’s because of the two star clusters, the V-shaped Hyades and small but distinctive stars of the Pleiades. Also, if you orient yourself with the famous constellation of Orion, you’ll know you’re looking in the right place.

First find Orion by looking for its three Belt stars. Orion and Taurus are next-door neighbors on the sky’s dome. In fact, Taurus rises above the horizon first. So by the time Orion is risen, you can use its Belt stars to draw a line upward to find Aldebaran and the two clusters of Taurus.

The stars of the Bull

Furthermore, Taurus is home to two particularly bright stars: Aldebaran and Elnath. Aldebaran is the easier of the two to find because it’s brighter, it’s part of the V-shape of the Hyades and it has a reddish hue.

For good reason, stargazers think of Aldebaran as the Bull’s fiery eye. Aldebaran is the 14th brightest star in the sky. It shines at magnitude 0.85. Although it may look like part of the Hyades cluster, it’s much closer. Aldebaran lies 65 light-years distant. The other stars of the Hyades are about 150 light-years away.

Elnath marks the end of one of Taurus the Bull’s horns. It’s on the opposite side of the Bull’s head from Aldebaran. Elnath is the 2nd brightest star in Taurus after Aldebaran. It shines at magnitude 1.68. Relatively nearby, Elnath lies about 130 light-years away, in the direction of the Milky Way’s anticenter.

The Crab Nebula

In addition, Taurus holds an excellent deep-sky target that you can spot with binoculars or a small telescope. Messier 1, or the Crab Nebula, is what’s left of a star after it exploded in a supernova. As a result, it lit up the daytime sky for over a month in 1054 CE.

Now, the Crab Nebula shines at magnitude 8.4. Plus, it’s easy to find since it lies near a star in Taurus named Zeta Tauri. While Elnath is the point of one of the Bull’s Horns, Zeta Tauri is the other.

Taurus the Bull in mythology and timekeeping

According to Greek mythology, the constellation Taurus commemorates the god Zeus. That’s because Zeus changed himself into a beautiful white Bull to win the affections of the Phoenician princess Europa. After Europa hopped onto the Bull’s back, the Bull swam across the Mediterranean Sea, taking Europa all the way to the island of Crete. Later, Zeus and Europa became the parents of Minos, the legendary king of Crete.

Meanwhile, the Zuni of New Mexico used the Pleiades cluster as an agricultural calendar. When the Pleiades – which the Zuni called the Seed Stars – disappeared into the western dusk in spring, they knew it was safe to plant their seeds, as the danger of frost had passed. However, the Zuni also knew the planting must be done before the Pleiades reappeared in the east before sunrise. Otherwise, immature plants would succumb to autumn frosts.

And the Zuni were hardly alone in their reverence for the Pleiades star cluster. Indeed, probably no other star formation has enjoyed such worldwide renown for timekeeping, celebration and storytelling.

Bottom line: Taurus the Bull resides near the constellation Orion. It contains two famous star clusters that are easy to spot: the Pleiades and the Hyades.

The constellations of the zodiac

Taurus the Bull in the evening sky
Gemini the Twins, home to 2 bright stars
Cancer the Crab and its Beehive Cluster
Leo the Lion and its backward question mark
Virgo the Maiden in northern spring skies
Libra the Scales, a zodiacal constellation
Scorpius the Scorpion is a summertime delight
Sagittarius the Archer and its famous Teapot
Capricornus the Sea-goat has an arrowhead shape
Aquarius the Water Bearer and its stars
Pisces the Fish, 1st constellation of the zodiac
Say hello to Aries the Ram
Born under the sign of Ophiuchus?

The post Meet Taurus the Bull in the February evening sky first appeared on EarthSky.

The Hyades: a nearby star cluster

With the exception of the Ursa Major Moving Group, the Hyades cluster is the closest star cluster to Earth, at a distance of 150 light-years. This cluster is very easy to spot in the night sky, because it has a compact and distinctive shape of the letter V. The bright star Aldebaran is part of the V.

The V shape represents the Face of the Bull in the constellation Taurus. Aldebaran represents the Bull’s fiery red eye.

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In fact, the Hyades cluster is easy to find by using Orion’s Belt, a compact and noticeable line of three blue-white stars in the constellation Orion the Hunter. Draw a line westward (generally toward your sunset direction) through the Belt stars, and you will come to the bright reddish star Aldebaran, the Bull’s fiery red eye.

Although Aldebaran isn’t a true member of the Hyades star cluster, this bright star is a great guide to this cluster. In fact, Aldebaran is only about 65 light-years distant. The Hyades lies about 2 1/2 times farther off. This is what we call a “line-of-sight coincidence.”

Use binoculars or telescope to see the Hyades star cluster

The V-shaped figure of stars (except Aldebaran) highlights the brightest of the Hyades’ few hundred stars. A dozen or more Hyades stars are visible to the unaided eye in a dark country sky, but several dozen of the cluster’s stars can be resolved through binoculars or low power in a telescope. From the Northern Hemisphere, the Hyades are best seen in the evening sky from around January to April.

The constellation Taurus the Bull is home to another bright star cluster, the Pleiades. The Pleiades cluster is more distant than the Hyades at some 430 light-years away. Both the Hyades and Pleiades are easily visible to the unaided eye. Also, both are enhanced by viewing with binoculars.

History and mythology of the Hyades star cluster

According to sky lore, the teary Hyades are the daughters of Atlas and Aethra, who are forever crying for their brother Hyas, who was killed by a lion or a boar. The Hyades are the half-sisters to the Pleiades, the daughters of Atlas and Pleione. The gods purposely kept Atlas’ daughters – the Hyades and the Pleaides – out of reach of Orion, giving them a safe haven from his lustful pursuits.

So the gods transformed Hyas into the constellation Aquarius, and the lion that killed him into the constellation Leo. The gods placed Aquarius and Leo on opposite sides of the sky for Hyas’ protection. That’s why Aquarius and Leo do not appear in the same sky together. As one constellation sets in the west, the other rises in the east, and vice versa.

Hyades science

Although the Hyades and Pleaides are half-sisters in mythology, science finds no close relationship in space between these two star clusters.

Astronomers find that the Pleiades are composed of hot blue-white suns in the heyday of youth. So that puts the age of the cluster at about 100 million years. In contrast, the cooler red giant and white dwarf stars found in the Hyades indicate a vastly older cluster over 600 million years old.

Interestingly, astronomers suspect an actual kinship between the Hyades cluster and the Beehive Star Cluster in the constellation Cancer the Crab. Even though these two star clusters are separated from one another by hundreds of light-years, they are akin in age and travel in a similar direction in space. This leads astronomers to believe that these clusters might have originated from the same gaseous nebula some 700 to 800 million years ago.

Is the Hyades cluster being destroyed?

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Bottom line: On January and February evenings, look for a V-shaped pattern of stars. The Hyades star cluster represents the face of Taurus the Bull. The cluster is easy to spot and beautiful through binoculars.

The post The Hyades star cluster: The Face of Taurus the Bull first appeared on EarthSky.

The Winter Circle or Winter Hexagon

The Winter Circle (or Hexagon) is a large circular pattern, made of some of the brightest stars in the Northern Hemisphere’s winter sky (or the Southern Hemisphere’s summer sky). It isn’t a constellation. It’s an asterism, or prominent group of stars that form a noticeable pattern. In addition, the Winter Circle has a smaller asterism inside it, called the Winter Triangle.

The Winter Circle is big! Strictly speaking, you’ll see this circular pattern of 1st-magnitude stars – the brightest stars in our sky – from six different constellations: Rigel in Orion the Hunter, Aldebaran in Taurus the Bull, Capella in Auriga the Charioteer, Pollux (and its forever companion Castor) in Gemini the Twins, Procyon in Canis Minor the Lesser Dog and Sirius in Canis Major the Greater Dog. Also, an additional 1st-magnitude star, Betelgeuse in Orion the Hunter, lies toward the center of the Circle.

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When is the Winter Circle (or Hexagon) visible?

So, like all stars, those in the Winter Circle rise and set some four minutes earlier with each passing night. Indeed, by late January, the Winter Circle will have risen high enough above the northeastern horizon so it’s visible by about 7 p.m. local time. Then, if you look around midnight, the Winter Circle will be high above the southern horizon. And later, after about 3 a.m. local time, it sinks toward the southwestern horizon, with some of it setting in the west before sunrise.

Then, in late February and early March, the Winter Circle is in your southern sky at nightfall and early evening.

Finding the Winter Circle

First, to find the Winter Circle (or Hexagon), find the easily recognizable constellation of Orion the Hunter. Indeed, its three belt stars give it away. Then, look for the bright bluish star to the lower right. This star is Rigel, the southwest corner of the Winter Circle and the first of the six stars in the Circle. By the way, Rigel is the brightest star in Orion and the seventh brightest star in the night sky.

Now draw a line through Orion’s Belt stars upward to find Aldebaran, the ruddy eye of Taurus the Bull. Aldebaran is the second star in the Circle and the brightest star in Taurus. As a matter of fact, Aldebaran is the fourteenth brightest star in the sky.

Next, continue upward in a counterclockwise direction to find the next bright star, Capella in Auriga the Charioteer. Capella is the third star on our journey and the northernmost point of the Winter Circle. In fact, Capella is the sixth brightest star in the heavens.

Completing the Circle

Then, as we start to wind down the other side of the Circle, we run into two bright stars, the Twins Stars in Gemini the Twins. Pollux, the brighter of the two, is our fourth corner in the Circle, and you’ll notice its “twin,” Castor, is just a bit fainter. Pollux is the sky’s 17th brightest star, and Castor is the 24th.

Our second-to-last stop around the Winter Circle is the bright star below the Twins Stars, Procyon. Procyon is the brightest star in Canis Minor the Lesser Dog, and in fact one of only two named stars in the constellation. For such a “minor” constellation, Procyon shines brilliantly as the seventh brightest star in the sky.

Finally, we come down to the southernmost star in the Winter Circle and the brightest of them all: Sirius in Canis Major the Greater Dog. Sirius is the brightest star in the Winter Circle and in the entire night sky. In fact, only the moon and some planets can outshine Sirius.

Finding the Winter Triangle

After you’ve found the Winter Circle, look inside it to find another asterism. That’s the Winter Triangle. First, take the last two stars of the Circle, Sirius and Procyon, then head toward the center of the Circle. That’s where you’ll find reddish star Betelgeuse, marking the shoulder of Orion. Betelgeuse makes the third corner of the Winter Triangle. Betelgeuse is the 10th brightest star in the sky and second brightest star in Orion.

The Circle is big and contains areas of the Milky Way

Furthermore, to get an idea of the Circle’s humongous size, the span from the southernmost star, Sirius, to the northernmost star, Capella, covers about 1/3 of the dome of the sky.

Then for a bonus, on a dark and clear moonless night, you can see the soft-glowing river of stars that we call the Milky Way meandering right through the center of the Winter Circle.

Bottom line: The Winter Circle, aka the Winter Hexagon, is a giant shape made from some of the brightest stars in the sky, including Rigel, Aldebaran, Capella, Pollux, Procyon and Sirius.

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The post Meet the Winter Circle, aka the Winter Hexagon first appeared on EarthSky.

On August evenings, we look toward the center of our Milky Way galaxy. And in January and February, we do the opposite. We look opposite the galaxy’s center, toward the galactic anticenter and the galaxy’s nearest outer edge. The star Elnath (aka Beta Tauri, and sometimes called Alnath) in the constellation Taurus the Bull is the closest bright star on our sky’s dome to the galactic anticenter.

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How to find Taurus’ 2nd brightest star

Elnath is easy to find if you learn to recognize the Face of the Bull in the constellation Taurus. The Face of the Bull in Taurus is shaped like the letter V. The V-shape is fairly easy to pick out from the background stars. These stars are members of the Hyades Cluster. By mid-January, you can find the V-shape nearly overhead about three hours after sunset. This V-shape includes the brightest star in Taurus, red Aldebaran.

If you extend the right side of the letter V (the side that’s opposite Aldebaran), you come to the star Elnath. Elnath represents the Northern Horn of Taurus the Bull. It’s the 2nd-brightest star in Taurus after Aldebaran, which represents the Bull’s bloodshot eye.

So, Elnath isn’t quite as bright as Aldebaran. But it’s also part of a noticeable pattern, and it’s blue-white in color.

Use Orion to find Taurus and Elnath

Can’t find the Face of the Bull? Try finding Orion the Hunter first, an extremely prominent constellation. You can recognize Orion for its Belt, a short, straight row of three medium-bright stars.

Draw a line upward through Orion’s Belt to find Aldebaran and the V-shape group of stars outlining the Bull’s Face. Extend the lines off the top of the V to locate the two stars marking the tips of the Bull’s horns. The northern and brighter horn star is Elnath.

When and where to look for Elnath

In the Northern Hemisphere, we see Taurus and its stars on winter evenings. Elnath stands opposite the sun around mid-December and thus rises around sunset and sets around sunrise. In January and February, Elnath is already up in the southeast at sunset. By June, Elnath will be lost to the sun’s glare and won’t be seen at all. Excepting June, however, you can see Elnath for at least part of the night throughout the year.

Elnath stands a bit north of the ecliptic, the annual pathway of the sun in front of the background stars. Because the moon’s path is always near the ecliptic, the moon swings close to Elnath every month. Generally, the moon swings to the south of Elnath. On occasion, the moon swings far enough north that it occults – passes directly in front of – Elnath. We are currently in the midst of a series of occultations that will last until April 11, 2027.

How to locate the Milky Way’s anticenter

The galactic anticenter lies about 3 degrees to the east of the star Elnath. Three degrees is about the amount of sky that your thumb covers when held at arm’s length. The galactic anticenter isn’t a place, it’s just a direction in the sky from our perspective on Earth. Elnath is about 130 light-years away, whereas the outskirts of our galaxy’s disk are many thousands of light-years away. So Elnath is much closer and just shows the direction.

While the closest bright star to the galactic anticenter is Elnath in Taurus, the anticenter isn’t in Taurus. Instead, it lies in a neighboring constellation, Auriga the Charioteer.

Science of the star Elnath

Elnath sparkles white and is tinged in blue. This star’s color indicates that it has a hot surface temperature of about 13,600 Kelvin (13,300 Celsius or 24,000 Fahrenheit). Contrast this to the surface temperature of our yellow-colored sun, which is 5,800 Kelvin (5,500 C or 10,000 F).

According to the star expert Jim Kaler, Elnath has 4.5 times the sun’s mass and shines with the firepower of 700 suns.

Elnath’s position is RA: 5h 26m 17.5s, dec: +28° 36′ 27″

Bottom line: The galactic anticenter is the position opposite the Milky Way’s center from our viewpoint on Earth. If you want to look toward the anticenter, gaze toward Elnath. This star is the 2nd-brightest star in the constellation Taurus the Bull and is just 3 degrees from the galactic anticenter, which lies nearby in the constellation Auriga.

The post Elnath is a bright star close to the galactic anticenter first appeared on EarthSky.

November 3, 2024, ushers in the earliest solar noon – for the whole year and for the entire globe – by the clock. Solar noon is a natural rather than artificial construct, although our clocks and calendars measure its continual shift throughout the year. Solar noon – aka midday – refers to that passing instant when the sun reaches its highest point for the day, midway between sunrise and sunset. If you reside along the center line of your time zone, then solar noon – or midday – comes at 11:43 a.m. by your clock every year in early November. If you’re not on your time zone’s center line – and most of us aren’t – solar noon happens a bit earlier or later by your clock, depending on your offset from your time zone’s center line.

Obscure? Possibly. But the shift in solar noon is tied to a phenomenon that many people around the world might notice in the coming weeks. That is, the earliest solar noon of the year is a prelude to the year’s earliest sunset in the Northern Hemisphere – and the year’s earliest sunrise in the Southern Hemisphere.

You thought the earliest sunset for the Northern Hemisphere came at the December solstice? It doesn’t. It happens well before that solstice, for a reason that’s related to the earliest solar noon on November 3.

Earliest and latest solar noons, and the length of the day. The first several days of November, from everywhere worldwide, the days (as measured from one solar noon to the next) are almost exactly 24 hours in duration. Thereafter, day by day, solar noon comes later and later by the clock, lessening the discrepancy between sun time and clock time. At long last – on December 25, 2024 – the sun and the clock agree with one another, with solar noon coming at 12 noon by the clock (for those at the center line of a given time zone).

Although the sun and clock will agree on December 25, 2024, the duration of the solar day – as measured from one solar noon to the next – will continue to exceed 24 hours each day for another six weeks.

Finally, the latest solar noon will arrive on or near February 11, at 12:14 p.m. by the clock (at the time zone center line).

And, for everyone, everywhere worldwide, solar noon comes some 30 minutes earlier by the clock on November 3, 2024, than it will on February 11, 2025.

Want to know the clock time for solar noon (midday) at your location? Visit Sunrise Sunset Calendars, remembering to check the solar noon box.

Want to know the time difference between sun and clock for any date? Go to AstroPixels.com and look under the equation of time column.

Solar noon and earliest sunset (and/or sunrise). So … November 3, 2024, marks the earliest solar noon of the year for the whole globe. What’s more, residents at the Earth’s equator have their earliest sunrise and sunset on November 3. That’s because, at the equator, the daylight hours remain virtually the same throughout the year – so the earliest sunrise, earliest solar noon and earliest sunset all fall on the same day.

Elsewhere – within the tropical and temperate regions of the world – the shortest period of daylight happens on the day of the winter solstice, and the longest period of daylight on the summer solstice. So if you live near the Arctic Circle, your earliest sunset doesn’t happen until around the December (winter) solstice; or if you live near the Antarctic Circle, your earliest sunrise doesn’t take place until around the December (summer) solstice.

That’s in spite of the earliest solar noon coming in early November all over the world.

Read more: December solstice starts shortest season

If you live north of the equator but south of the Arctic Circle, your earliest sunset occurs somewhere between November 3, 2024, and December 21, 2024. In the Northern Hemisphere, those living closer to the equator have an earlier date for their earliest sunset; and those lodging closer to the Arctic Circle have a later date for their earliest sunset.

We give the approximate dates for the earliest sunset in the Northern Hemisphere:

15 degrees north latitude
Earliest sunset on or near November 23

30 degrees north latitude
Earliest sunset on or near December 1

45 degrees north latitude
Earliest sunset on or near December 10

60 degrees north latitude
Earliest sunset on or near December 17

In the Southern Hemisphere, it’s your earliest sunrise that takes place between November 3, 2024, and December 21, 2024. The closer you live to the equator, the earlier the date for the earliest sunrise; and the closer you live to the Antarctic Circle, the later the date for the earliest sunrise. Because comparable latitudes north/south of the equator have the same approximate dates for earliest sunset/earliest sunrise, the dates for the Southern Hemisphere’s earliest sunrises can be gleaned from the listing above.

In the Northern Hemisphere, the latest sunrise must wait till after the Northern Hemisphere’s December winter solstice; and in the Southern Hemisphere, it’s the latest sunset that must wait till after the Southern Hemisphere’s December summer solstice. Those living closer to the Arctic or Antarctic Circles have an earlier date for their latest sunrise/latest sunset; and those lodging closer to the Earth’s equator have a later date for their latest sunrise/latest sunset. Here are the approximate dates for the Northern Hemisphere’s latest sunrise/Southern Hemisphere’s latest sunset at various latitudes:

60 degrees latitude: December 27
45 degrees latitude: January 2
30 degrees latitude: January 11
15 degrees latitude: January 23

Two reasons account for the unequal length of the solar day over the year. First and foremost, the tilt of the Earth’s axis causes the solar day to be more than 24 hours long around the solstices yet less than 24 hours long around the equinoxes. However, Earth’s eccentric orbit plays a secondary role, either accentuating or lessening the effect. At the December solstice, the Earth is some 3 million miles (5 million km) closer to the sun, and moving more swiftly in its orbit, than on the June solstice. Therefore, the longer-than-average solar day at the December solstice (24 hours + 30 seconds) outlasts the longer-than-average solar day at the June solstice (24 hours + 13 seconds).

Bottom line: November 3 brings the year’s earliest solar noon – that is, earliest midday – by nature’s clock. It’s a harbinger of the Northern Hemisphere’s earliest sunset.

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The post Year’s earliest solar noon on November 3 first appeared on EarthSky.

Want to entertain your friends on New Year’s Eve? Give them a quick tour of the heavens, and show them Sirius, the brightest star in the sky. It has the nickname the Dog Star, because it’s part of the constellation Canis Major the Greater Dog. Sirius might also be called the New Year’s star. It’ll ring in 2024 by reaching its highest point in the sky around the stroke of midnight. That’s true for every New Year’s Eve.

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How to find the star Sirius

So how can you find Sirius? Well, for starters, it’s the brightest star in Earth’s night sky. In fact, its name means sparkling or scorching.

The only points of light that can shine brighter than Sirius are some of the planets. If you’re scanning the dark sky and aren’t sure which point of light is Sirius, here’s a sure-fire way to know. Look for the prominent Belt stars of the constellation Orion the Hunter. Because Orion’s Belt always points to Sirius, you can identify Sirius easily.

Sirius is up late for the party

So Sirius is highest in the sky at midnight during every turn of the year. In short, astronomers call this a midnight culmination of Sirius. Thus, as the New Year rings in, Sirius is at its highest point in the sky.

To clarify, by midnight, we mean the middle of the night, that is, midway between sunset and sunrise. Like the sun, the stars rise in the east and travel westward across the sky. When the sun or any star is in the eastern half of the sky, it’s climbing upward or ascending. When the sun or any star is in the western sky, it’s descending downward. Therefore, midway between rising and setting, the sun or any star reaches its highest point in the sky.

Because the stars rise and set two hours earlier with each passing month, Sirius will be highest up for the night around 10 p.m. local time on February 1.

Bottom line: Look for the star Sirius at midnight culmination – highest in the sky around midnight, that is, midway between sunset and sunrise – every New Year’s Eve.

The post The star Sirius rings in the New Year first appeared on EarthSky.

Aries the Ram isn’t a noticeable constellation. It ranks as the 11th smallest out of the 12 zodiacal constellations. And its stars are only moderately bright. But the giant planet Jupiter lies in front of Aries now. And December and January are great months to spot this faint constellation, with Jupiter’s help. Although Aries has few bright stars, there’s much to see telescopically within this constellation. And it figures prominently into the history of astronomy.

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How to see Aries the Ram

The best time to behold the Mighty Ram is when the Earth is on the other side of the sun from this constellation. The months around the December solstice are especially good for viewing Aries the Ram in all his starlit majesty. During those months, this constellation shines above the eastern horizon at nightfall and stays out for most of the night. Aries culminates – reaches its highest point in the sky – at about 10 p.m. your local time in late November, 8 p.m. your local time in late December and 6 p.m. your local time in late January.

Because Aries isn’t a particularly prominent constellation, you’ll want a dark country sky, on a night when there’s no moon. The three stars depicting the Ram’s bust – Hamal, Sheratan and Mesartim – suddenly brighten in a dark sky. In fact, it’s as if someone had turned up the dimmer switch. By the way, a small telescope reveals that Mesartim is a double star.

Fortunately, the head of the Ram is fairly easy to locate. You’ll find it midway between these two signposts: the Pleiades star cluster to the east and the Great Square of Pegasus to the west. The Ram’s head is turned backward, as if admiring the Pleiades, or perhaps his own golden fleece.

What is the First Point of Aries?

The First Point of Aries marks the sun’s position in front of the constellations of the zodiac on the Northern Hemisphere’s spring equinox or Southern Hemisphere’s autumnal equinox. This equinox happens yearly on or near March 20, as the sun crosses the celestial equator, going from south to north.

Also, the First Point of Aries, which is actually in the constellation Pisces nowadays, defines the coordinate system on the celestial sphere. The First Point of Aries always coincides with zero degrees right ascension and zero degrees declination. Right ascension is the equivalent of longitude here on Earth. Declination on the sky’s dome is the equivalent of latitude.

In addition, the First Point of Aries is one of two places on the celestial sphere where the ecliptic and celestial equator intersect. Then the First Point of Libra resides 180 degrees east of the First Point of Aries, marking the September equinox point on the celestial sphere.

What is the First Point in Pisces?

Since the Earth’s rotational axis wobbles full circle relative to the backdrop stars in about 26,000 years, Polaris doesn’t remain the North Star forever. In turn, that means the equinox points don’t remain fixed relative to the stars of the zodiac. So, the March equinox point drifts westward (along the ecliptic) through the constellations of the zodiac at about one degree (two sun diameters) in 72 years, or 30 degrees in 2,160 years.

Hence, the March equinox point passed out of the constellation Aries and into the constellation Pisces in 68 B.C. Even so, we still call this equinox point the First Point of Aries.

Hamal, brightest star in Aries

Hamal, or Alpha Arietis, is the brightest star in Aries. This orange giant star shines at magnitude 2 and lies a bit more than 65 light-years from Earth.

In fact, Hamal means head of the ram, a fitting name. Also, sailors once used Hamal to help in navigation. And the star is the 50th brightest in the sky.

The celestial Ram in star lore

In Greek mythology, Aries represents the supernatural Ram that was sent by Zeus to rescue the children of Athamus, the King of Thebes, from political intrigue. Phrixus and his sister Helle were about to meet their demise, but the flying Ram, which could both speak and reason, took them away in the nick of time.

The children held on tight as the Ram flew them away for the safety of Colchis, an ancient kingdom bordering the eastern shore of the Black Sea. Unfortunately, Helle fell into the sea and drowned before reaching their destination. Hellespont – the ancient name for the Dardanelles Strait near Istanbul, Turkey – marks the place of her death, named in her honor.

Phrixus survived the long trip to Colchis. He gave thanks by sacrificing the Ram to Zeus, hanging it in a sacred grove where the fleece turned to gold. Later, Jason and the Argonauts recovered the Golden Fleece.

Bottom line: How to see the constellation Aries the Ram, plus info about this constellation in the history of astronomy and mythology.

All 12 (13) zodiac constellations

Taurus? Here’s your constellation
Gemini? Here’s your constellation
Cancer? Here’s your constellation
Leo? Here’s your constellation
Virgo? Here’s your constellation
Libra? Here’s your constellation
Scorpius? Here’s your contellation
Sagittarius? Here’s your constellation
Capricornus? Here’s your constellation
Aquarius? Here’s your constellation
Pisces? Here’s your constellation
Aries? Here’s your constellation

The post Aries the Ram – and Jupiter – in the evening sky first appeared on EarthSky.