Come to know the legendary Pleiades star cluster

The Pleiades star cluster is also famously known as the Seven Sisters. Or, to some, it’s known as Messier 45 (M45) on the list of Messier objects. The Pleiades is visible from almost every part of the globe. It’s seen from as far north as the North Pole and farther south than the southernmost tip of South America. It looks like a tiny misty dipper of stars.

In fact, many ancient cultures had myths and stories associated with the Pleiades. In Greek mythology, the Pleiades were the seven daughters of Atlas, a Titan who held up the sky, and the oceanid Pleione, protectress of sailing. The sisters were Maia, Electra, Alcyone, Taygete, Asterope, Celaeno and Merope. The Pleiades were sometimes said to be nymphs in the train of Artemis. They were half-sisters of the seven Hyades. The Hyades pattern is another star cluster near the Pleiades stars.

According to a Polynesian legend, the Pleiades was once a single star: the brightest in the sky. The Polynesian god Tane disliked this star bragging about its beauty. So the god smashed the star into pieces, creating the Pleiades star cluster.

The modern-day festival of Halloween originates from an old Druid rite that coincided with the midnight culmination of the Pleiades cluster. People believed the veil dividing the living from the dead is at its thinnest when the Pleiades culminates – reaches its highest point in the sky – at midnight.

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

Sibling stars traveling through space together

In both myth and science, the Pleiades are sibling stars. Modern astronomers say the stars were born from the same cloud of gas and dust some 100 million years ago. This gravitationally bound cluster of several hundred stars looms some 430 light-years distant. Also, these sibling stars drift through space together at about 25 miles per second (40 kilometers per second). Many of these stars shine hundreds of times more brightly than our sun.

How to find the Pleiades

If you’re familiar with the famous constellation Orion the Hunter, it can help you confirm you’ve found the Pleiades. See the three stars in a row in Orion? That’s Orion’s Belt. Now draw a line through these stars to the V-shaped pattern of stars with a bright star in its midst. The V-shaped pattern is the Face of Taurus the Bull. The bright star in the V – called Aldebaran – depicts the Bull’s Eye. Then, when you go a bit past Aldebaran, you’ll see the Pleiades cluster. It marks the Bull’s Shoulder.

In our Northern Hemispheres skies, the Pleiades cluster is associated with the coming winter season. It’s easy to imagine this misty patch of icy-blue suns as hoarfrost clinging to the dome of night. So frosty November is the month of the Pleiades, because it’s at this time that the Pleiades shines from dusk until dawn. But you can see the Pleiades cluster in the evening sky well into April.

The Pleiades and Aldebaran

The star name Aldebaran comes from an Arabic word for follower. It’s thought to be a reference to this star’s forever chasing the Pleiades across the heavens. As a general rule, the Pleiades cluster rises into the eastern sky before Aldebaran rises, and sets in the west before Aldebaran sets.

The only exception to this rule happens at far southern latitudes. For example, at South America’s Tierra del Fuego, Pleiades rises a short while after Aldebaran rises.

Legend of the Lost Sister

Most people see six, not seven, Pleiades stars in a dark country sky.

However, the story about the lost 7th Pleiad appears universal. The astronomer Robert Burnham Jr. found the lost Pleiad myth prevalent in the star lore of European, African, Asian, Indonesian, Native American and Aboriginal Australian populations.

Moreover, Burnham suggested that the “lost Pleiad” may have basis in fact. Modern astronomy has found that the 7th-brightest Pleiades star – Pleione – is a complicated shell star that goes through numerous permutations. Naturally, these changes can cause this star to vary in brightness.

Plus, people with exceptional eyesight have been known to see many more stars in the cluster. Claims go up as high as 20 stars. Agnes Clerke, an astronomer and writer in the late 1800s, reported that Michael Maestlin, the mentor of Johannes Kepler, mapped out 11 Pleiades stars before the invention of the telescope.

To see more than six or seven Pleiades stars, you must have very good eyesight (or a pair of binoculars). And you must be willing to spend time under a dark, moonless sky. Stephen O’Meara, a dark-sky connoisseur, claims that eyes dark-adapted for 30 minutes are six times more sensitive to light than eyes dark-adapted for 15 minutes. But the surest way to see additional Pleiades stars is to look at this cluster using some optical aid.

The Pleiades photo gallery

Bottom line: The Pleiades – or Seven Sisters – is a star cluster that’s a popular target for observers in the late fall and winter in the Northern Hemisphere.

The post The Pleiades – or 7 Sisters – known around the world first appeared on EarthSky.

Great Square of Pegasus

Look east just after dark for the Great Square of Pegasus around the time of the September equinox (in 2023, it was on September 23). Throughout late September and October evenings, the Great Square will be ascending in the eastern evening sky. The Great Square consists of four stars of nearly equal brightness. Specifically, they are Scheat, Alpheratz, Markab and Algenib. Incidentally, the constellation Pegasus represents a Flying Horse. But the Great Square – a prominent asterism within Pegasus – is a landmark of the Northern Hemisphere’s autumn sky.

To find the Great Square

First of all, to find the Great Square, use the Big Dipper to star-hop to Polaris, the North Star. Then draw an imaginary line from Polaris until you land an outer star on the W or M-shaped constellation Cassiopeia the Queen.

Finally, a line from Cassiopeia faithfully escorts you to the Great Square of Pegasus.

The moon can guide you to the Great Square

The moon will often be near the Great Square. Here are charts for late September and October 2023.

Also check EarthSky’s Visible planets and night sky guide for current information.

Great Square is an asterism, not a constellation

Like the Big Dipper, the Great Square of Pegasus isn’t a constellation. Instead, it’s an asterism, or noticeable pattern on our sky’s dome. And, like the Big Dipper, the Great Square can be used to help you find other sky treasures, the most notable being the Andromeda galaxy, another famous sight on autumn evenings in the Northern Hemisphere.

Read more: 2 ways to find the Andromeda galaxy

Great Square of Pegasus: A big square of nothing

Often, at events where many are stargazing for the first time, one may hear:

… the Great Square has nothing in it.

But, of course, the Great Square isn’t empty. In fact, no part of the night sky is really empty. But because the stars inside the Great Square are so faint, the unaided eye can’t easily detect them. However, if you use binoculars or a small telescope you can see many stars within the Great Square. Counting stars inside the Great Square is a good way to determine how dark your sky is when observing.

First discovery of an exoplanet orbiting a sun-like star

One of the most famous faint stars near the Great Square is 51 Pegasi. In 1995, astronomers announced in the journal Nature they’d discovered a planet around this star, and it is now called 51 Pegasi b. After a few months of skepticism from the astronomical community, it was confirmed that the first planet beyond our solar system had been discovered.

Now we know that at least 12 stars in Pegasus have exoplanets, and astronomers have confirmed more than 5,500 exoplanets in our Milky Way galaxy. The astronomers who found 51 Pegasi b – Michel Mayor of the University of Geneva and Didier Queloz at the Cavendish Laboratory and Geneva University – received the 2019 Nobel Prize in Physics for their discovery.

Some books say that 51 Pegasi is visible with the unaided eye alone. But it’s a challenge. Using binoculars, look roughly halfway between Scheat and Markab in the Great Square of Pegasus. Note that you won’t be able to see the planets. Pegasus 51 is approximately 50 light-years away from Earth.

Mythology of the Great Square of Pegasus

You might recall that Pegasus was a winged horse in Greek mythology. The constellation Pegasus is one of seven constellations in the autumn sky that explain why it’s never a good idea to claim a mortal’s beauty is greater than that of the gods. This story is plastered all over the autumn night sky, and Pegasus figures into it prominently.

The story goes that Cassiopeia the Queen bragged that she (or her daughter Andromeda the Princess) was more beautiful than the immortal Nereids, or sea nymphs. This angered the gods, who asked the sea-god Poseidon to take revenge. The punishment was that Cepheus the King and Cassiopeia had to sacrifice Andromeda to Cetus the Whale (sometimes called a sea monster). Andromeda was chained to a rock at sea. She was about to be gobbled up by Cetus, when she saw Perseus the Hero – riding Pegasus the Flying Horse – swooping toward her.

Perseus had a trick up his sleeve. He faced Cetus, holding up the head of the Gorgon Medusa. It’s said the sight of the Medusa turned Cetus to stone. Then Perseus whacked the chains that bound Andromeda and freed her. They rode off on Pegasus the Flying Horse and lived happily ever after. Later, Zeus placed all of them in the sky as stars, along with Delphinus the Dolphin, who’d provided comfort to Andromeda.

Bottom line: How you can see the Great Square of Pegasus star pattern.

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The post Great Square of Pegasus gallops into the autumn sky first appeared on EarthSky.

Come to know the Teapot of Sagittarius

Our Milky Way galaxy is a vast collection of hundreds of billions of stars. We’re not in the galaxy’s center, but instead about 2/3s of the way out from center, in one of the Milky Way’s spiral arms. On August evenings, all of us on Earth can gaze toward the galaxy’s center in a dark sky. In fact, the band of the Milky Way gets broader and brighter in the direction toward the center. Plus, in that direction, you’ll find a famous asterism called the Teapot, in the constellation Sagittarius.

The Teapot’s pattern is distinctive. Once you spot it, it’s easy to imagine as an earthly teapot. You’ll find it southward on August evenings from the Northern Hemisphere, and overhead from the Southern Hemisphere.

Even if your sky isn’t dark, once you find the Teapot, you can use it to guide your mind’s eye to the star-rich center of our galaxy. A supermassive black hole lies at the galaxy’s heart. As a matter of fact, it has some 4 million times the mass of our sun. It’s called Sagittarius A* (Sagittarius A-Star).

How to spot the Teapot

You’ll want a fairly dark sky to find the Teapot (a suburban sky will likely work, if you’re not standing under a streetlight). You can see the Teapot even if you can’t see the starry band of the Milky Way. If you’re in the Northern Hemisphere, look southward on August evenings a couple of hours after sunset. If you’re in the Southern Hemisphere, look overhead.

The Teapot and Sagittarius are best viewed during the evening hours from about July to September.

Want a more exact location for Sagittarius? Try Stellarium, which will let you set a date and time from your exact location on the globe.

The Teapot looks like its name

The constellation of Sagittarius is supposed to be a centaur, a mythical half man/half horse creature, carrying a bow and arrow. But good luck spotting the centaur in these stars.

On the other hand, the Teapot – unlike many star patterns – looks like its namesake. That’s because the Teapot appears to have a handle, spout and lid, as any earthly teapot would. And just be sure to head to a dark sky for your best views of this Milky Way region.

Once you’ve found the Teapot, assuming you have a dark sky, you can see “steam” billowing out of the spout. Gaze into the midst of this “steam” – into the thickest part of it – and you’ll be gazing toward the center of our Milky Way galaxy.

The Teapot is highest in the evening sky in August

Because the sun passes in front of Sagittarius from about December 18 to January 20, the Teapot isn’t visible then. However, about half a year later – on July 1 – the Teapot climbs to its highest point for the night around midnight (1 a.m. daylight saving time or DST), when it appears due south as seen from the Northern Hemisphere or due north as seen from the Southern Hemisphere. In August, the Teapot – and the Milky Way center – reach their highest points for the night during the evening hours.

By the way, another noteworthy point lies in the direction of the Teapot in space. It’s the point at which the sun shines on the December solstice around December 21 each year.

The center of our Milky Way

The center of our galaxy is some 30,000 light-years away. We can’t see directly into it, because this region is shrouded by dust and gas clouds. But studies of astronomers have shown that, when we look in this direction, we’re looking toward the supermassive black hole located at our galaxy’s heart. This black hole has some 4 million times our sun’s mass. It’s known as Sagittarius A*.

Now sweep the area around the Teapot with binoculars or a telescope. You’ll see many faint fuzzy objects pop into view. They’re star clusters and nebulae (gas clouds) located in the disk of our galaxy, in the direction toward the galaxy’s center.

So, find the Teapot on a dark night – when the moon is out of the way – and enjoy all it has to offer.

Bottom line: As you gaze toward the famous Teapot asterism in the constellation Sagittarius, you’re looking toward the center of our Milky Way galaxy.

The post Teapot of Sagittarius points to Milky Way center first appeared on EarthSky.

Scorpion’s Crown and associates

Scorpius the Scorpion is one of the easiest constellations to see in the sky. It is, in fact, a large J-shaped figure. The bright red star Antares lies at the Scorpion’s heart. Likewise, a curved arc of three stars – Acrab, Dschubba and Fang – mark the Scorpion’s head. They’re known as the Crown of the Scorpion. The upper part of Scorpion – Antares at the heart, and the three stars at the Crown – are beautiful to look at and fascinating to contemplate. Also, Antares and these three stars are part of a nearby grouping of young stars known as the Scorpius–Centaurus Association.

Young stars born from the same cloud

The Scorpius–Centaurus Association is an OB association. Generally speaking, that’s a term astronomers use to describe a collection of young stars formed from the same giant cloud of dust and gas. Indeed, most stars in our galaxy formed this way, without much in the way of gravitational bonds to each other. This is in contrast to stars that form in more compact gravitationally-bound open or globular star clusters. Observations of these associations provide scientists with a deeper understanding of how stars form and evolve. However, they can be a challenge to study because member stars, at least the ones relatively close to us, cover a large area in the sky.

Members of the Scorpius–Centaurus Association are, on average, about 420 light-years away. Moreover, they appear in several southern constellations, including the upper part of Scorpius, Centaurus the Centaur, Lupus the Wolf and Crux the Southern Cross. This association is of great interest to astronomers because it’s the nearest OB association to us. In Scorpius, members of the association, known as Upper Scorpius, may be just 11 million years old (this is very young in the range of stellar lifespans) while other members of the Scorpius–Centaurus Association range to as much as 15 million years in age.

The stars and their distances and temperatures

Astronomers have directly measured distances for over 400 brighter members of the Scorpius–Centaurus Association. In addition, they have identified much fainter, lower mass, stars from spectroscopic surveys. Overall, the exact number of stars in this association remains unknown but it’s likely in the few thousands.

Most stars visible to us are massive hot blue stars, like those in the Scorpion’s Crown. For example, the largest star in the Upper Scorpius sector is Antares, with a mass almost 15 times that of our sun. However, the masses of stars in the association run the gamut from very massive stars to very low mass brown dwarf stars.

Generations of stars: Dead stars cause new star birth

Much larger stars once existed throughout the Scorpius–Centaurus Association. They’re now long gone, having exploded as supernovae. Still, they continue to be important players in subsequent star formation. Indeed, these supernovae left ghostly traces of their presence – bubble-like cavities within the cloud complexes – when powerful shockwaves from the explosions initially swept through the massive molecular cloud. Farther away from the supernovae, the shockwaves, their power a bit muted from traveling large distances, passed through some cloud regions. Thus, triggering new rounds of star formation as their energy compressed dust and gas in their paths.

On his website, astronomer Thomas Preibisch wrote about the Scorpius-Centaurus Association’s possible history. (Some dates written here are modified based on new research). About 15 to 17 million years ago, star formation began in a region of the massive cloud located in what is today’s constellations of Centaurus and Lupus. Then, around 12 million years ago, a very massive star in that region exploded as a supernova, creating a tremendous shockwave. Finally, about 11 million years ago, energy from that shockwave reached molecular clouds in the upper part of Scorpius, triggering star formation. That’s how the Scorpion Crown stars and Antares were born.

Supernova in Scorpion’s crown triggered a shockwave

Massive stars in this new family emitted powerful ultraviolet radiation and stellar winds that cleared out much of the remaining cloud material, putting a stop to further star formation. However, the most massive star of that family exploded as a supernova, sending out another shockwave. Now, that shockwave is moving through a neighboring cloud complex, called Rho Ophiuchi, triggering another cycle of star formation.

Bottom line: The three stars that make up the head of Scorpius the Scorpion are part of a young collection of stars formed from the same cloud of gas and dust, called the Scorpius-Centaurus Association.

The post The Scorpion’s Crown and its stellar neighborhood first appeared on EarthSky.

How to find the Northern Cross

The Northern Cross is a clipped version of the constellation Cygnus the Swan. It’s an asterism, or pattern of stars that’s not a recognized constellation. It lies embedded within another much larger asterism: the Summer Triangle. You’ve got to have a dark sky and a good imagination to see a swan in the stars of Cygnus. But the Northern Cross is easy to see, even if your sky is less than pristine.

Here’s step one for finding the Northern Cross. Look for the asterism’s most brilliant star, Deneb. Deneb marks the top of the Northern Cross. It’s also well known as one of the three bright stars of the Summer Triangle, along with Vega and Altair.

Now, look for a bright star roughly halfway between Altair and Vega and slightly offset toward Deneb. That’ll be Albireo. Although only a modestly bright star, Albireo is easy to see on a clear, dark night. There are no similarly bright stars near Albireo, so it’s fairly easy to find.

Once you locate Deneb and Albireo, you’re halfway to piecing together the Northern Cross. All you need now is the crossbar, which most people see as three moderately bright stars. As you can see in the illustration above, these three stars extend about halfway out into the wings of Cygnus the Swan.

Backbone of the Milky Way

When you look at the Northern Cross, you’re looking directly into the flat disk of our galaxy, the Milky Way. In fact, the galactic plane (equator) runs right through the Northern Cross, encircling the sky above and below the horizon. So the Northern Cross serves as a great signpost for a view of our home galaxy. In a dark sky on a northern summer evening, the Milky Way appears as a luminescent river of haze passing directly along the length of the Northern Cross. You can see this hazy band stretching all the way across the sky on late July and August evenings.

You probably know that this haze is actually countless stars. So, these stars will emerge beautifully through binoculars, as will the star fields, star clusters and nebulae that abound within the disk of the Milky Way!

Northern Cross as a marker of seasons

As seen from mid-northern latitudes, the Northern Cross is out for at least part of the night all year around. Plus, it’s out all night in summer. On Northern Hemisphere summer nights, the Northern Cross shines in the east at nightfall, sweeps high overhead after midnight, and swings to the west by daybreak. When you see the Northern Cross in the east on summer evenings, it’s sideways to the horizon.

By the time northern autumn arrives, the Northern Cross is still out from nightfall until midnight, but it appears high overhead in the evening and sets in the northwest after midnight.

And when winter comes, the Northern Cross is standing upright over your northwest horizon before midnight.

Bottom line: The Northern Cross is an asterism – or recognizable pattern of stars – within the constellation Cygnus the Swan. Here’s how to find it in your sky.

The post The Northern Cross: Find the backbone of the Milky Way first appeared on EarthSky.

On any evening from July until about November – if you have a dark sky – you can look within the famous Summer Triangle for a tiny but recognizable cluster of stars. Most people call it the Coathanger cluster. Two other names are Brocchi’s cluster and Collinder 399. The Coathanger is a tiny asterism, or pattern of stars (not a constellation).

It isn’t a true open star cluster, but only a chance alignment of physically unrelated stars.

It looks like its namesake, making it easy to spot with binoculars and a dark sky. But you have to know just where to look. It’s visible from both the Northern and Southern Hemispheres.

Coathanger cluster within the Summer Triangle

Do you already know the Summer Triangle stars? If not, click here. The Summer Triangle is easy to spot as a large triangle in the east on northern summer evenings. Three bright stars mark its corners: Deneb in the constellation Cygnus the Swan, Vega in Lyra the Harp, and Altair in Aquila the Eagle.

The Milky Way – the edgewise view into the flat disk of our galaxy – runs right through the Summer Triangle. So there are many beautiful little clusters here, plus, of course, the great and glorious Dark Rift of the Milky Way.

If you can find the Summer Triangle, you can find the Coathanger. Just be sure to look from a dark rural location, and have some binoculars handy. The cluster is located along a line between two Triangle stars, Vega and Altair. The image below illustrates the view.

Albireo can help you find the Coathanger

First – to find the Coathanger – you need to find a slightly fainter star, beloved Albireo. This star is located in the midst of the Summer Triangle. It’s also seen as the bottom of a second asterism within the Summer Triangle, called the Northern Cross.

Albireo is found at the base of the Northern Cross.

Albireo to Alpha Vulpeculae to the Coathanger

Got Albireo? Now for some specifics on finding the Coathanger. With binoculars, look for the brightest star in the vicinity of Albireo. That star is called Alpha Vulpeculae, which appears as a double star through binoculars (though the two stars are not gravitationally bound).

Draw an imaginary line from Albireo through Alpha Vulpeculae to locate the Coathanger. In most binoculars, Alpha Vulpeculae and the Coathanger fit within the same binocular field of view, though just barely.

Notice that six stars form the bar of the Coathanger, while four stars make up the hook. From mid-northern latitudes, the Coathanger often appears upside-down. That’s why some people call it the Ski Lift.

When should you look?

Our sky chart above shows the stars as they appear from the Northern Hemisphere in middle July around midnight (1 a.m. daylight saving time).

Because the stars return to the same place in the sky some two hours earlier with each passing month, this sky chart also shows star positions for about 10 p.m. (11 p.m. daylight time) in mid-August, 8 p.m. (9 p.m. daylight time) in mid-September and 6 p.m (7 p.m daylight time) in mid-October.

Since these stars shine from south to overhead at these times (as seen from the Northern Hemisphere), you might want to sprawl out on a reclining lawn chair, with your feet pointing southward. A reclining position saves neck strain.

The Coathanger’s position is RA: 19h 26.47′; Dec: 20^o 11.93′

Bottom line: Star-hop to the Coathanger – a tiny asterism that really looks like its namesake – via the stars Albireo and Alpha Vulpeculae.

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The post Coathanger cluster: It does look like its name first appeared on EarthSky.

Summertime is Summer Triangle time

It’s summer here in the Northern Hemisphere. The days are long. The sun is at its height in the midday sky. And the summer sky is with us, too. Watch for the famous Summer Triangle, now ascending in the eastern sky on these late June and July evenings.

The Summer Triangle isn’t a constellation. It’s an asterism, or noticeable pattern of stars. This pattern consists of three bright stars in three separate constellations – Deneb in the constellation Cygnus the Swan, Vega in the constellation Lyra the Harp, and Altair in the constellation Aquila the Eagle.

Learn to recognize the Summer Triangle asterism now, and you can watch it all summer as it shifts higher in the east, then finally appears high overhead in the late northern summer and early northern autumn sky.

How to find the Summer Triangle

As night falls in June or July, look east for a sparkling blue-white star. That will be Vega, in Lyra. Reigning at the apex of the celebrated Summer Triangle, Vega is also the brightest of the Summer Triangle’s three stars, which are all bright enough to be seen from many light-polluted cities.

Look to the lower right of Vega to locate the Summer Triangle’s second brightest star. That’s Altair, the brightest star in the constellation Aquila the Eagle. A ruler (12 inches, 30 cm) held at arm’s length fills the gap between these two stars.

Look to the lower left of Vega for another bright star: Deneb, the brightest in the constellation Cygnus the Swan and the third brightest in the Summer Triangle. An outstretched hand at arm’s length approximates the distance from Vega to Deneb.

It’s difficult to convey the huge size of the Summer Triangle. But you’ll see it. These three bright stars – Vega, Deneb and Altair – will become summertime favorites.

Summer Triangle as a road map to the Milky Way

If you’re lucky enough to be under a dark starry sky on a moonless night, you’ll see the great swath of stars passing between the Summer Triangle’s Vega and Altair. The star Deneb bobs in the middle of this river of stars, which arcs across dark summer skies. This sky river is, of course, the edgewise view into our own Milky Way galaxy. Although every star you see with the unaided eye is a member of the Milky Way. And at this time of year we can see clearly into the galaxy’s flat disk, where most of the stars congregate. By August and September, we will have a good view toward the galaxy’s center.

Once you master the Summer Triangle, you can always locate the Milky Way on a clear, dark night. How about making the most of a dark summer night to explore this band of stars, this starlit boulevard with its celestial delights? Use binoculars to reveal the gossamer beauty of the haunting nebulae and bejeweled star clusters along this starlit trail.

Nature’s seasonal calendar

Also, the Summer Triangle serves as a stellar calendar, marking the seasons. So when the stars of the Summer Triangle light up the eastern twilight dusk in middle to late June, it’s a sure sign of the change of seasons, of spring giving way to summer. However, when the Summer Triangle is high in the south to overhead at dusk and early evening, the Summer Triangle’s change of position indicates that summer has ebbed into fall.

A word about asterisms

As we mentioned above, asterisms aren’t constellations; they’re just patterns on the sky’s dome. Constellations generally come to us from ancient times. In the 1930s, the International Astronomical Union officially drew the boundaries of the 88 constellations we recognize today.

Meanwhile, you can make up and name your own asterisms, in much the same way you can recognize shapes in puffy clouds on a summer day.

Of course, some asterisms are so obvious that they’re recognized around the world. And the Summer Triangle is one of these.

Bottom line: On June and July evenings, you’ll find the Summer Triangle in the east at nightfall. It swings high overhead after midnight and sits in the west at daybreak.

The post Summer Triangle: Star pattern of the season first appeared on EarthSky.

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The Southern Cross – also known as Crux – is an iconic constellation for people south of the equator. It’s visible every clear night, and its stars shine brightly enough to be picked out pretty easily even from urban locations.

If you’re in the Northern Hemisphere, you too can see the famous Southern Cross. You just need to be far enough south, and know where and when to look.

Where can you see the Southern Cross?

At 35 degrees south latitude and all latitudes farther south, you can see the Southern Cross all night, all year round. In that part of the Southern Hemisphere, the Southern Cross is circumpolar: it is always above the horizon, as it circles the sky close to the celestial pole.

However, for much of the Northern Hemisphere – including most of the United States – the Southern Cross can never be seen. It never rises above the horizon.

You can see see all of Crux from the U.S. state of Hawaii. In the contiguous U.S., you need to be in southern Florida or Texas (about 26 degrees north latitude or farther south). Even from the far-southern contiguous U.S., you have a limited viewing window for catching the Southern Cross. It has to be the right season of the year. It has to be the right time of night. And you have to look in the right direction: south!

When to look?

For the Northern Hemisphere’s tropical and subtropical regions, May is a good time to find Crux in the evening sky. It is visible in other months, but not at such a convenient time. In March, you have to wait until about 1 a.m. to catch the Southern Cross at its highest elevation. In December and January, you have to catch it before dawn.

No matter the hour or date, Crux climbs to its highest point in the sky when it’s due south. The Cross is fairly easy to visualize, because it stands upright over the horizon.

Use the Big Dipper as a guide.

Although the Big Dipper is a fixture of Northern Hemisphere skies, it has a close kinship with the Southern Cross. The Big Dipper and the Southern Cross are highest in the sky at the same time of year.

Remember, spring up and fall down: the Big Dipper soars highest in the sky during the Northern Hemisphere’s spring. When the Big Dipper is seen above Polaris, the North Star, the Southern Cross can be seen standing over the southern horizon in Texas and southern Florida.

In the Southern Hemisphere it works the same way, just in reverse. The Big Dipper can be seen in the Southern Hemisphere from about 26 degrees south latitude and all latitudes farther north. But to spot it, it has to be the right season and the right time of night. When the Southern Cross sails highest in the Southern Hemisphere sky, the “upside-down” Big Dipper is seen just above the northern horizon at latitudes near the tropic of Capricorn (23.5 degrees south latitude).

The Southern Cross in navigation.

When European sailors journeyed south of the equator, they found that the North Star had disappeared below the horizon. As they sailed even farther south, the Big Dipper dropped out of sight as well. Unlike the Northern Hemisphere, the Southern Hemisphere has no bright pole star to highlight the celestial pole. Fortunately, the Southern Cross acts as a navigational aid.

There are various ways to find the direction due south using the Southern Cross as a guide. For example, a line drawn from the star Gacrux through the star Acrux points in the general direction of the south celestial pole (the point in the sky directly above Earth’s south pole). Discover more ways to locate south using the Southern Cross.

Bottom line: The Southern Cross can be seen from the Northern Hemisphere, as long as you’re below 26 degrees north and know when and where to look!

The post How to see the Southern Cross from the Northern Hemisphere first appeared on EarthSky.

The Big and Little Dipper

The Big Dipper is one of the easiest star patterns to locate in Earth’s sky. It’s visible just about every clear night in the Northern Hemisphere, looking like a big dot-to-dot of a kitchen ladle. As Earth spins, the Big Dipper and its sky neighbor, the Little Dipper, rotate around the North Star, also known as Polaris.

From the northern part of the Northern Hemisphere, the Big and Little Dippers are in the sky continuously. In fact, they are always above your horizon, circling endlessly around Polaris. So given an unobstructed horizon, latitudes north of the 35th parallel (the approximate location of the Mediterranean Sea and Tennessee’s southern border) can expect to see the Big Dipper at any hour of the night every day of the year.

As for the Little Dipper, it’s circumpolar – always above the horizon – as far south as the Tropic of Cancer (23.5 degrees north latitude).

If you can spot the Big Dipper, then you’re on your way to finding the Little Dipper and the North Star, Polaris, too.

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The Big Dipper rotates around Polaris every night and changes by season

Just remember the old saying spring up and fall down. So on spring and summer evenings in the Northern Hemisphere, the Big Dipper shines at its highest in the evening sky. Then, on autumn and winter evenings, the Big Dipper sweeps closer to the horizon.

The Big Dipper rotates around the North Star or Polaris during the different seasons. Do you ever wonder why you can see the same stars night after night? Did you ever wonder why when you see a double rainbow, the rainbow on the top has the colors in reverse? pic.twitter.com/dTSOy7kAab

— Samantha Burns (@SamanthaRose369) November 27, 2022

Here’s how to find Polaris and the Little Dipper

Notice that the Big Dipper has two parts, a bowl and a handle. Next, look for the two outer stars in the bowl of the Big Dipper. They are called Dubhe and Merak, and they’re known as The Pointers. An imaginary line drawn between them points to Polaris, the North Star. And, once you have Polaris, you can find the Little Dipper, too … if your sky is dark enough.

That’s because Polaris marks the end of the Little Dipper’s Handle.

So why isn’t the Little Dipper as easy to pick out as the Big Dipper? That’s because the stars between Polaris and the outer bowl stars – Kochab and Pherkad – are rather dim. As a matter of fact, you’ll need a dark country sky to see all seven of the Little Dipper’s stars.

The Big and Litter Dipper are not constellations

Also, the Big Dipper isn’t a constellation. It’s an asterism, or noticeable pattern of stars. The Big Dipper is a clipped version of the constellation Ursa Major the Greater Bear. And the stars of the Big Dipper outline the Bear’s tail and hindquarters.

The Little Dipper is also an asterism, these stars belonging to the constellation Ursa Minor the Little Bear.

The Big Dipper will change over time

Astronomers sometimes speak of the fixed stars, but know the stars aren’t truly fixed. Stars move in space. Thus the star patterns that we see today as the Big and Little Dippers will, slowly but surely, drift apart over time.

But even 25,000 years from now, the Big Dipper pattern will look nearly the same as it does today. Astronomers have found that the stars of the Big Dipper (excepting the pointer star, Dubhe, and the handle star, Alkaid) belong to an association of stars known as the Ursa Major Moving Cluster. These stars, loosely bound by gravity, drift in the same direction in space.

In 100,000 years, this pattern of Big Dipper stars (minus Dubhe and Alkaid) will appear much as it does today! But there will be some differences, as illustrated in the video below:

Star lore behind the Big and Little Dipper

In the star lore of the Mi’kmaq nation in northern Canada, the Big Dipper is also associated with a bear, but with a twist. The Mi’kmaq see the Big Dipper bowl as a Celestial Bear, and the three stars of the handle as hunters chasing the Bear. In the Mi’kmaq tale of the Celestial Bear, in autumn, the hunters finally catch up with the Bear, and it’s said that the blood from the Bear colors the autumn landscape

In another version of the story, the Celestial Bear hits its nose when coming down to Earth, with its bloody nose giving color to autumn leaves. When the Celestial Bear is seen right on the northern horizon on late fall and early winter evenings, it’s a sure sign that the hibernation season is upon us.

In ancient times, the Little Dipper formed the wings of the constellation Draco the Dragon. But when the seafaring Phoenicians met with the Greek astronomer Thales around 600 B.C., they showed him how to use the Little Dipper stars to navigate. Thereby, Thales clipped Draco’s wings, to create a constellation that gave Greek sailors a new way to steer by the stars.

In Thales’ day, the stars Kochab and Pherkad (rather than Polaris) marked the approximate direction of the north celestial pole. That’s the point in the sky that is directly above the Earth’s North Pole.

To this day, Kochab and Pherkad are still known as the Guardians of the Pole.

Big Dipper images from EarthSky Community Photos

Bottom line: You can find the Big Dipper and Little Dipper in northern skies any time of year. The North Star, Polaris, is located at the end of the Little Dipper’s handle.

The post The Big and Little Dipper: How to find them first appeared on EarthSky.

The Spring Triangle heralds warmer weather

Around the time of the March equinox, a trio of wide-spread stars rises in the east after dark. The Spring Triangle announces the slide into shorter nights and warmer weather. Regulus in Leo the Lion is the first to rise above the horizon, having risen before the sun has even set. It’s followed by Arcturus in Boötes the Herdsman. And, just a bit later, Spica in Virgo the Maiden joins the group. These three bright stars create a narrow pyramid stretching up from the horizon.

The Spring Triangle is entirely above the horizon before midnight in March. And by early April, its three stars are visible by mid-evening (midway between sundown and midnight).

Once you come to know it, when you see the Spring Triangle stars above the houses across the street, you can almost feel the warm springtime air.

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The Spring Triangle is an asterism

Like the sky’s other seasonal shapes (for instance, the Summer Triangle and Winter Circle or Hexagon), the Spring Triangle isn’t a constellation. It’s not one of the 88 regions of the sky officially recognized as constellations by the International Astronomical Union.

Instead, it’s an asterism, an unofficial but recognizable pattern of stars that can be in one constellation or in multiple constellations. Asterisms are what many of us would pick out as constellations, if we didn’t know any constellations. That’s because they’re often the sky’s most recognizable patterns.

Let’s look at how to find these stars so we can watch them move across the night sky.

Regulus

As soon as it’s dark in March, look for a bright yellowish star twinkling above the eastern horizon. That’s Regulus, and it’s easy to confirm if you’ve spotted the right star. If the star you’re targeting marks the period in a backward question mark pattern of stars, you’ve got it. This question mark shape is another asterism known as the Sickle in Leo. The curve of the question mark traces the head of the lion and Regulus is the Lion’s heart.

When we look at Regulus we only see one star, but it’s actually a four-star system. From about 79 light-years away, the light from the four stars makes one point of light in the night sky. The brightest star in this system is a yellow supergiant about three times the size of our sun.

Arcturus

Next up is Arcturus, the brightest star of the three in the Spring Triangle. For those at northerly latitudes, Arcturus is the second-brightest star visible on the sky’s dome, after Sirius, which is currently in the southwestern sky. (Those at more southerly latitudes, like the southern U.S., can see the sky’s actual second-brightest star, Canopus, in the south.) Arcturus is a gorgeous old red giant about 37 light-years away. Billions of years in the future, when the sun has burnt up its own hydrogen fuel supply, it will turn into a star similar to the type Arcturus is now.

Spica

If Arcturus has risen, Spica is not far behind. Look for Spica lower in the sky than Arcturus – and father toward the south, or right – of the others. From a distance of 262 light-years away, Spica appears to us on Earth to be a lone bluish-white star in a quiet region of the sky. But Spica consists of two stars and maybe more. The pair are both larger and hotter than our sun, and they’re separated by only 11 million miles (less than 18 million km). They orbit their common center of gravity in only four days.

A triangle inside the triangle

If you can spot the Spring Triangle, you may notice there’s a second triangle inside the larger triangle. The smaller triangle excludes Regulus but includes yellowish Denebola, a double star about 36 light-years away that marks the Lion’s tail. Denebola is the second brightest in Leo. To see this second triangle, see the chart below.

The Spring Triangle is less attention-grabbing than the Winter Circle (or Hexagon) and the Summer Triangle. If you’re having trouble finding it, there’s another way. Use the Big Dipper for extra help.

Finding the Spring Triangle

Toward the north, look for the Big Dipper, called the Plough in the United Kingdom. This time of year, by mid-evening, it’s ascending in the northeast. If you draw a line from the two stars at the end of the Dipper’s bowl or blade – Dubhe and Merak – and extend it toward the south, you’ll reach Regulus.

Then, follow the curve of the Dipper’s handle away from the bowl to arc to Arcturus and continue the line downward to speed on down to Spica.

Surprisingly enough, the Spring Triangle is bigger than its more famous summertime cousin, and it’s almost as big across as the Winter Hexagon. Yet it’s not one of the best-known star patterns.

Once you’ve found the Spring Triangle, you’ll enjoy it year after year. Maybe because it appears as spring is about to arrive, this pattern seems full of optimism for good things to come!

Bottom Line: Look for a sign of the changing seasons in the heavens as the Spring Triangle, made up of the stars Regulus, Arcturus and Spica, rises above the horizon in the east over the next couple of months.

Read more: Arc to Arcturus, the springtime star

The post Spring Triangle rises late at night, heralding the season first appeared on EarthSky.