Antares and Betelgeuse may be colossal stars, but we take it to the next level of stellar monstrosity with a visit to UY Scuti, a star that makes our Sun seem no bigger than a pinpoint.
This illustration shows the approximate size of the red supergiant UY Scuti compared to the Sun. Philip Park / CC BY-SA 3.0
Stars range in size from red supergiants that if put in place of the Sun would reach beyond Saturn down to neutron stars that would fit comfortably within a limits of small city. Great examples of bright, well-known supergiants include Orion's Betelgeuse and Antares in Scorpius. The latter twinkles a fist to the lower left of Mars this week and shares its fiery color.
At ~1,000 times the size of the Sun, Betelgeuse is an impressive star to be sure, but it's no match for UY Scuti, currently the largest star known with a diameter around 1,700 times that of the Sun. It's a crazy-bright candle, too, with a luminosity 340,000 times greater than the Sun.
If you were to replace the Sun with UY Scuti, its photospheric fringes would extend outward some 735 million miles (1.2 billion kilometers) almost to Saturn. A beam of light would take some 7 hours to circle the star's circumference compared to 14.5 seconds for the Sun.
A selection of stellar giants, ranging from the orange giant Aldebaran up to the current size-record holder UY Scuti.
Jcpag2012 / CC BY-SA 4.0
You might think that such an enormous body would be easily visible with the naked eye, and it might be were it not 9,500 light-years away and squarely located in the Milky Way's Great Rift. After battling distance and dust, UY never gets brighter than magnitude +9 but can dip as low as +11.
UY Scuti shines with a ruddy glow. Haktarfone / CC BY-SA 3.0
Either way, it's still an easy catch in a 4-inch or larger telescope from reasonably dark skies. I observed it on May 22nd in a 10-inch reflector at 76× and can happily report the star hovers at the bright end of its range around magnitude +9.5. Even in full moonlight, I could detect its reddish hue.
Judging by its name, you've already guessed that UY Scuti's a variable star like so many of its supergiant brothers and sisters. Variations in the rate that the star burns helium, coupled with mass loss, cause it to undergo pulsations with a period of roughly 740 days.
UY Scuti's not difficult to find, located about 2° north of 5th-magnitude Gamma (γ) Scuti and 4° southwest of 4th-magnitude Alpha (α) Scuti just below the tail of Aquila. From the mid-United States, it climbs to 20° altitude by 11:30 p.m. local time in late May and 10:30 p.m. in mid-June.
While the map I've provided should get you right up to the star, you might also like to print out the AAVSO chart which shows the field in black-and-white reverse. Some observers find reverse maps easier to to use at the telescope.
This map, which shows stars to magnitude +10, plots the position of the luminous supergiant star UY Scuti, one of the largest stars known. Click to enlarge — pardon the pun! Stellarium
If UY Scuti whets your appetite for more monster madness, spring and summer abound with lesser though still impressive naked-eye supergiants such as Antares (750× solar), Rho Cassiopeiae (450× solar) and Alpha Herculis a.k.a. Rasalgethi (400× solar and a beautiful double star to boot). Not as well known but nearly as large as UY are V354 Cephei (1,520× solar) and RW Cephei. RW currently occupies the #3 spot in the list of largest stars with a diameter of 1,535 solar or larger than Jupiter's orbit.
Supergiants RW Cep and V354 Cep are within a stone's throw of the famed variable, Delta Cephei, an easy naked-eye star. V354 lies 45′ northeast of Delta, while RW Cep is 2.5° south of the star. All three are circumpolar from many U.S., Canadia, and European locations. Map: Bob King, Source: Stellarium
Lucky for us, both V354 Cep and RW Cep lie close to one of the most famous variables of all, Delta Cephei. Center Delta in your low power eyepiece and you're halfway there. RW shines around magnitude +6.5, so you can easily spot this fiery orange spark in binoculars; V354 will prove a little more challenging at its current magnitude of +11.7. You'll find AAVSO charts to which I've labeled the brighter stars to make a bit more intuitive here and here.
Use this wide-view locator map to point you toward RW Cep and V354 Cep, both of which sit close to Delta Cephei. The view is from latitude 40° N. Map: Bob King, Source: Stellarium
When describing stellar diameters, particularly the bloated red and yellow supergiants, determining a precise size is no easy task. Their atmospheres are so distended and vaporous, the diameters given in this article are best estimates and should be taken with a molecule of caution. Material lost through stellar winds creates shifting envelopes of gas and dust around each, making it tricky to say where star ends and winds begin.
Every one of these supergiants is a potential supernova candidate. Looking at them in the telescope, you can almost hear the sizzle of helium burning to carbon in their cores. As heat and pressure continue to forge new elements all the way up through iron, the stars will ultimately shut down, implode, and then explode as supernovae. Perhaps a tiny pulsar, a spinning neutron star the size of a city, will be left in the wake of the explosion. If so, in one fell swoop, the biggest stars will become the smallest.
My six-year old daughter is a question-asking machine. We were driving home from school a couple of days ago, and she was grilling me about the nature of the Universe. One of her zingers was, “What’s the Biggest Star in the Universe”? I had an easy answer. “The Universe is a big place,” I said, “and there’s no way we can possibly know what the biggest star is”. But that’s not a real answer.
So she refined the question. “What’s the biggest star that we know of?” Of course, I was stuck in the car, and without access to the Internet. But once I got back home, and was able to do some research, I learned the answer and thought I’d share it with the rest of you But to answer it fully, some basic background information needs to be covered first. Ready?
Solar Radius and Mass:
When talking about the size of stars, it’s important to first take a look at our own Sun for a sense of scale. Our familiar star is a mighty 1.4 million km across (870,000 miles). That’s such a huge number that it’s hard to get a sense of scale. Speaking of which, the Sun also accounts for 99.9% of all the matter in our Solar System. In fact, you could fit one million planet Earths inside the Sun.
Using these values, astronomers have created the terms “solar radius” and “solar mass”, which they use to compare stars of greater or smaller size and mass to our own. A solar radius is 690,000 km (432,000 miles) and 1 solar mass is 2 x 1030 kilograms (4.3 x 1030 pounds). That’s 2 nonillion kilograms, or 2,000,000,000,000,000,000,000,000,000,000 kg.
Artist’s depiction of the Morgan-Keenan spectral diagram, showing the difference between main sequence stars. Credit: Wikipedia Commons
Another thing worth considering is the fact that our Sun is pretty small, as stars go. As a G-type main-sequence star (specifically, a G2V star), which is commonly known as a yellow dwarf, its on the smaller end of the size chart (see above). While it is certainly larger than the most common type of star – M-type, or Red Dwarfs – it is itself dwarfed (no pun!) by the likes of blue giants and other spectral classes.
Classification:
To break it all down, stars are grouped based on their essential characteristics, which can be their spectral class (i.e. color), temperature, size, and brightness. The most common method of classification is known as the Morgan–Keenan (MK) system, which classifies stars based on temperature using the letters O, B, A, F, G, K, and M, – O being the hottest and M the coolest. Each letter class is then subdivided using a numeric digit with 0 being hottest and 9 being coolest (e.g. O1 to M9 are the hottest to coldest stars).
In the MK system, a luminosity class is added using Roman numerals. These are based on the width of certain absorption lines in the star’s spectrum (which vary with the density of the atmosphere), thus distinguishing giant stars from dwarfs. Luminosity classes 0 and I apply to hyper- or supergiants; classes II, III and IV apply to bright, regular giants, and subgiants, respectively; class V is for main-sequence stars; and class VI and VII apply to subdwarfs and dwarf stars.
The Hertzspirg-Russel diagram, showing the relation between star’s color, AM. luminosity, and temperature. Credit: astronomy.starrynight.com
There is also the Hertzsprung-Russell diagram, which relates stellar classification to absolute magnitude (i.e. intrinsic brightness), luminosity, and surface temperature. The same classification for spectral types are used, ranging from blue and white at one end to red at the other, which is then combined with the stars Absolute Visual Magnitude (expressed as Mv) to place them on a 2-dimensional chart (see above).
On average, stars in the O-range are hotter than other classes, reaching effective temperatures of up to 30,000 K. At the same time, they are also larger and more massive, reaching sizes of over 6 and a half solar radii and up to 16 solar masses. At the lower end, K and M type stars (orange and red dwarfs) tend to be cooler (ranging from 2400 to 5700 K), measuring 0.7 to 0.96 times that of our Sun, and being anywhere from 0.08 to 0.8 as massive.
Based on the full of classification of our Sun (G2V), we can therefore say that it a main-sequence star with a temperature around 5,800K. Now consider another famous star system in our galaxy – Eta Carinae, a system containing at least two stars located around 7500 light-years away in the direction of the constellation Carina. The primary of this system is estimated to be 250 times the size of our Sun, a minimum of 120 solar masses, and a million times as bright – making it one of the biggest and brightest stars ever observed.
Eta Carinae, one of the most massive stars known, located in the Carina constellation. Credit: NASA
There is some controversy over this world’s size though. Most stars blow with a solar wind, losing mass over time. But Eta Carinae is so large that it casts off 500 times the mass of the Earth every year. With so much mass lost, it’s very difficult for astronomers to accurately measure where the star ends, and its stellar wind begins. Also, it is believed that Eta Carinae will explode in the not-too-distant future, and it will be the most spectacular supernovae humans have ever seen.
In terms of sheer mass, the top spot goes to R136a1, a star located in the Large Magellanic Cloud, some 163,000 light-years away. It is believed that this star may contain as much as 315 times the mass of the Sun, which presents a conundrum to astronomers since it was believed that the largest stars could only contain 150 solar masses. The answer to this is that R136a1 was probably formed when several massive stars merged together. Needless to say, R136a1 is set to detonate as a hypernova, any day now.
In terms of large stars, Betelgeuse serves as a good (and popular) example. Located in the shoulder of Orion, this familiar red supergiant has a radius of 950-1200 times the size of the Sun, and would engulf the orbit of Jupiter if placed in our Solar System. In fact, whenever we want to put our Sun’s size into perspective, we often use Betelgeuse to do it (see below)!
Yet, even after we use this hulking Red Giant to put us in our place, we are still just scratching the surface in the game of “who’s the biggest star”. Consider WOH G64, a red supergiant star located in the Large Magellanic Cloud, approximately 168,000 light years from Earth. At 1.540 solar radii in diameter, this star is currently one of the largest in the known universe.
But there’s also RW Cephei, an orange hypergiant star in the constellation Cepheus, located 3,500 light years from Earth and measuring 1,535 solar radii in diameter. Westerlund 1-26 is also pretty huge, a red supergiant (or hypergiant) located within the Westerlund 1 super star cluster 11,500 light-years away that measures 1,530 solar radii in diameter. Meanwhile, V354 Cephei and VX Sagittarii are tied when it comes to size, with both measuring an estimated 1,520 solar radii in diameter.
The Largest Star: UY Scuti
As it stands, the title of the largest star in the Universe (that we know of) comes down to two contenders. For example, UY Scuti is currently at the top of the list. Located 9.500 light years away in the constellation Scutum, this bright red supergiant and pulsating variable star has an estimated average median radius of 1,708 solar radii – or 2.4 billion km (1.5 billion mi; 15.9 AU), thus giving it a volume 5 billion times that of the Sun.
However, this average estimate includes a margin of error of ± 192 solar radii, which means that it could be as large as 1900 solar radii or as small as 1516. This lower estimate places it beneath stars like as V354 Cephei and VX Sagittarii. Meanwhile, the second star on the list of the largest possible stars is NML Cygni, a semiregular variable red hypergiant located in the Cygnus constellation some 5,300 light-years from Earth.
A zoomed-in picture of the red giant star UY Scuti. Credit: Rutherford Observatory/Haktarfone
Due to the location of this star within a circumstellar nebula, it is heavily obscured by dust extinction. As a result, astronomers estimate that its size could be anywhere from 1,642 to 2,775 solar radii, which means it could either be the largest star in the known Universe (with a margin of 1000 solar radii) or indeed the second largest, ranking not far behind UY Scuti.
And up until a few years ago, the title of biggest star went to VY Canis Majoris; a red hypergiant star in the Canis Major constellation, located about 5,000 light-years from Earth. Back in 2006, professor Roberta Humphrey of the University of Minnesota calculated its upper size and estimated that it could be more than 1,540 times the size of the Sun. Its average estimated mass, however, is 1420, placing it in the no. 8 spot behind V354 Cephei and VX Sagittarii.
These are the biggest star that we know of, but the Milky way probably has dozens of stars that are even larger, obscured by gas and dust so we can’t see them. But even if we cannot find these stars, it is possible to theorize about their likely size and mass. So just how big can stars get? Once again, Professor Roberta Humphreys of the University of Minnesota provided the answer.
Size comparison between the Sun and VY Canis Majoris, which once held the title of the largest known star in the Universe. Credit: Wikipedia Commons/Oona Räisänen
As she explained when contacted, the largest stars in the Universe are the coolest. So even though Eta Carinae is the most luminous star we know of, it’s extremely hot – 25,000 Kelvin – and therefore only 250 solar radii big. The largest stars, in contrast, will be cool supergiants. Case in point, VY Canis Majoris is only 3,500 Kelvin, and a really big star would be even cooler.
At 3,000 Kelvin, Humphreys estimates that cool supergiant would be as big as 2,600 times the size of the Sun. This is below the upper estimates for NML Cygni, but above the average estimates for both it and UY Scutii. Hence, this is the upper limit of a star (at least theoretically and based on all the information we have to date).
But as we continue to peer into the Universe with all of our instruments, and explore it up close through robotic spacecraft and crewed missions, we are sure to find new and exciting things that will confound us further!
And be sure to check out this great animation that shows the size of various objects in space, starting with our Solar System’s tiny planets and finally getting to UY Scuti. Enjoy!
A galaxy pileup of 14 merging galaxies known as SPT2349 is currently the biggest known object in the universe.(Image credit: NRAO/AUI/NSF; S. Dagnello)
Editor's Note: This story was updated at 5:10 p.m. E.T.
There's nothing like staring up at the night sky to make you feel small.
But when looking out into the cosmos, you might also wonder: What is the most massive known object in the universe?
In some ways, the question depends on what is meant by the word "object." Astronomers have spotted structures like the Hercules-Corona Borealis Great Wall — a colossal filament of gas, dust and dark matter containing billions of galaxies that stretches for about 10 billion light-years in length — which could contend for the title of biggest object ever. But classifying this assembly as a unique object is problematic because it's hard to figure out exactly where it begins and ends.
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"Object" actually has a clear definition in physics or astrophysics, said Scott Chapman, an astrophysicist at Dalhousie University in Halifax, in the Canadian province of Nova Scotia. "That's something bound together by its own self-gravity," he said, such as a planet, star or the stars orbiting within a single galaxy.
With this in mind, it's a bit easier to figure out what's in the running for the most massive thing in the universe. The award could go to different entities depending on the scale being considered, but each prizewinner has provided scientists insights into the limits of size and mass in the cosmos. [Big Bang to Civilization: 10 Amazing Origin Events]
Biggest planet, star and galaxy cluster
A view of Jupiter from above its north pole, taken by Pioneer 11 in 1974. Jupiter is the biggest planet in our solar system, but far from the biggest known planet in the universe. (Image credit: NASA Ames)
For our relatively tiny species, the planet Earth is plenty big, at about 13 septillion lbs. (6 septillion kilograms) — or 13 with 24 zeroes after it. But it's not even the largest planet in the solar system, being dwarfed by the outer giants Neptune, Uranus, Saturn and mighty Jupiter, which weighs in at 4.2 octillion lbs. (1.9 octillion kg), or 4.2 with 27 zeroes after it. Researchers have uncovered thousands of planets orbiting other stars, including many that make our local giants look puny. Discovered in 2016, HR2562 b is the heaviest exoplanet found to date, with a mass 30 times that of Jupiter. At that size, astronomers are unsure whether to classify the behemoth as a brown dwarf, which would make it a type of small star rather than a planet. [By Jove! 7 Weird Facts About Jupiter]
Stars themselves can grow to enormous sizes, with the most massive known star, R136a1, being somewhere between 265 and 315 times heavier than our sun, which is a mind-boggling 4.4 nonillion lbs. (2 nonillion kg), or 4.4 with 30 zeroes after it. Located 130,000 light-years away in the Large Magellanic Cloud, a companion galaxy orbiting our Milky Way, R136a1 is so big and bright that the light it emits is actually tearing it apart, according to a 2010 study in the Monthly Notices of the Royal Astronomical Society. The electromagnetic radiation streaming from the star is powerful enough to carry away material from the surface, causing the star to lose about 16 Earth's worth of mass every single year. Astronomers are unsure exactly how such a self-destructive star could form and how much longer it will hold itself together.
The most massive stars can clock in at enormous weights; the biggest, captured in this image from the European Southern Observatory's Very Large Telescope, are about 256 times the mass of the sun and are located in RMC 136a, a stellar nursery located inside the Tarantula Nebula, in one of our neighboring galaxies, the Large Magellanic Cloud, 165 000 light-years away. (Image credit: ESO/VLT)
Galaxies are the next objects up the size scale of the cosmos. The Milky Way galaxy is already mind-bendingly massive, stretching 100,000 light-years from end to end, containing approximately 200 billion stars, and weighing about 1.7 trillion times the mass of our sun. But it can't compete with the central galaxy of the Phoenix Cluster, a leviathan 2.2 million light-years across that contains about 3 trillion stars, according to NASA. At the center of this beast is a supermassive black hole — the largest ever seen — with an estimated mass of 20 billion suns. The Phoenix Cluster itself is an enormous accumulation of approximately 1,000 galaxies all orbiting one another about 5.7 billion light-years away with a total mass of about 2 quadrillion suns, which is 2 with 15 zeros after it, according to a 2012 paper in the journal Nature.
But even that goliath can't compete with what is likely the most massive object ever seen — a recently discovered galactic protocluster known as SPT2349, which was described April 25 in the journal Nature.
"We hit the jackpot with this structure," Chapman, whose team uncovered the record-breaker, told Live Science. "More than 14 very massive individual galaxies crammed into the space of something not much larger than our Milky Way."
Spotted when the universe was just a tenth of its current age, the individual galaxies in this pileup will eventually combine into one gargantuan galaxy, the most massive in the universe. And it's just the tip of the iceberg, Chapman said. Further observations have revealed that the total structure contains around 50 additional galaxies that will all settle into an object known as a galactic cluster, in which many galaxies all orbit one another. The previous most massive record-holder, the appropriately named El Gordo Cluster, weighs the equivalent of 3 quadrillion (or 3 with 15 zeroes after it) suns, but SPT2349 is likely to outweigh it by at least four to five times.
That such an enormous object could form when the universe was just 1.4 billion years old was surprising to the researchers, since computer simulations suggested it would normally take much longer for such large objects to appear.
"The central massive galaxy forms incredibly early and much more explosively and rapidly than we would have imagined," Chapman said. "Just the blink of the eye on the cosmic timescales."
Given that humans have searched only a fraction of the sky for such things, even more massive objects might be lurking out there in the universe, he added.
Editor's Note: This story was updated to correct the name of the massive galaxy pileup that is the biggest known object. It is SPT2349, not the Dusty Red Core.
How to Find the Ten Brightest Stars in the Night Sky
From Aldebaran to Vega, these gleaming beacons dazzle Northern Hemisphere viewers at various times of the year and provide a useful entry point into amateur astronomy
Beginning to familiarize yourself with the night sky can feel daunting—with so many pinpricks of light above, parsing the constellations or identifying individual stars can be a lofty task. One starting point is to learn to find the brightest ones.
In a rural sky dense with stars, the brightest serve as helpful signposts to orient yourself. And even just outside of cities, these luminous objects can compete with light pollution.
“You can see the brightest stars even from suburban locations,” says amateur astronomer Bob King, who is based in Duluth, Minnesota, and writes a column on skywatching for the Duluth News Tribune. “You don’t have to go to a rural countryside location to see those. But I always encourage people to do that, if possible.”
These stars are associated with various times of year, and being able to identify them can help you clock the shifting of the seasons and visualize how the Earth is moving through space. “We have certain flowers that appear, certain kinds of weather in different seasons, and we come to love those things,” King adds. “The same thing applies to the stars.”
But perhaps most of all, recognizing the brightest stars can point you to a handful of skyward sights. Each of them has the distinction of being the brightest or second brightest in its constellation, acting as a great celestial landmark. “All these bright stars are portals to so many things,” King says.
Each star is also a potential spark for amateur astronomers’ curiosity. Stare long enough at Betelgeuse and you might begin to wonder why it appears red, or why Vega gleams sapphire blue. Observing the colors of stars on this list can provide a hint to their temperatures—with hotter stars appearing blue-white and cooler stars glowing red or orange.
These stars are ranked based on their apparent magnitude, or how bright they seem from our vantage point on Earth. This is influenced not only by how much light the star actually emits, but also by how close it is to our solar system. Some of the farthest stars on this list are much more luminous than the nearer ones, but they look to be fainter due to their distance.
Technically, our own sun is the brightest star in our skies—but it doesn’t count for this list. After the sun has set, a new suite of shining beacons appear. Here are the ten brightest, as seen from the Northern Hemisphere, with tips on how to spot them.
Sirius
An illustration of the “dog star” Sirius A and its smaller companion Sirius B, nicknamed “the pup” NASA, ESA and G. Bacon (STScI)
Known as the “dog star” for its place amid the constellation Canis Major, Sirius is the brightest star in the night sky. The vivid star is one of the nearest to Earth, at just 8.6 light-years away. It also has some company: A small, white dwarf called Sirius B orbits the dog star, and because of its smaller nature, astronomers have termed this companion “the pup.”
Sirius is a natural stargazing target because of how bright it appears. But it also puts on a stunning show in color, especially when viewed through binoculars. All stars appear to twinkle as their light gets distorted in Earth’s atmosphere. In some cases, the atmosphere can act like a prism, refracting colors out of a star’s light. The effect is strongest when stars appear low on the horizon.
“Sirius is by far the most fabulous twinkler, and it can look like a firecracker,” King says. “You get a yellow Sirius, deep red Sirius, blue Sirius—and it all happens in a fraction of a second. It’s a kaleidoscope of colors.”
How to find Sirius: Sirius is best seen after sunset in winter. Follow the three stars of Orion’s belt to the east, and you’ll see Sirius as a bright beacon. Along with the red star Betelgeuse at Orion’s shoulder and Procyon in Canis Minor, Sirius forms part of an easily identifiable star pattern called the “winter triangle.”
Arcturus
From the Big Dipper in the center of this photo, follow the handle out in an arc to find Arcturus, which lies above the mountains near the horizon. Alan Dyer / VW Pics / Universal Images Group via Getty Images
Because Sirius is seen when looking toward the south, the orange star Arcturus earns the distinction of being the brightest star in northern skies. Arcturus is 25 times the diameter of the sun, but its surface is several thousand degrees cooler. The star is moving rapidly, racing toward the constellation Virgo at nearly 324,000 miles per hour.
Arcturus was once central to a public demonstration of scientific and technological progress at the World’s Fair held in Chicago in 1933. Astronomers had recently calculated that Arcturus is approximately 40 light-years away—and the last time Chicago had hosted a World’s Fair was 40 years prior. This meant that, feasibly, light from the star that reached Earth during the 1933 fair was emitted around the first time Chicago was home to such a spectacle. (Now, astronomers know Arcturus is 36.7 light-years away.)
To power the fair’s lights, four observatories around the United States focused the star’s light onto photocells, a new technology at the time. The photocells converted that light to an electric current and transported it via telegraph lines to flip a switch that illuminated Chicago.
How to find Arcturus: Located in the northern constellation Boötes, the herdsman, the star can be seen from spring to fall in the United States. Beginning at the Big Dipper in Ursa Major, follow the handle in an arc away from the dipper’s “bowl,” and it will point toward the gleaming Arcturus. Continue along that same imaginary trajectory, and you’ll find Spica, the brightest star in the constellation Virgo (though it doesn’t quite make this top ten list).
Vega
Vega, in the constellation Lyra, shines brightly amid its nearby stars. ched cheddles via Flickr under CC BY-NC-ND 2.0
At roughly 25 light-years away, Vega is a rapidly spinning star in the constellation Lyra. A fixture of the summer sky for Northern Hemisphere viewers, Vega has associations with warmer months for many astronomers. “When I see the star Vega coming up in the east on a late winter night … it gives me hope that the end of winter might be coming,” King says.
On cosmic timescales, Vega is a young star at around 455 million years old—about one-tenth the age of our own sun. But it’s aging much more quickly. As a bigger star, it will burn through its fuel faster than our sun will, so Vega is already about halfway through its lifetime. Vega moves in a different plane than the planets in our solar system—so when we view it, we see its pole.
Besides our own sun, Vega was the first star to be photographed, with a 20-minute daguerreotype exposure taken at Harvard College Observatory in 1850. It was also the first star to have its spectrum measured, revealing information about which elements it contains.
How to find Vega: Blue-white Vega, in the Lyra constellation, forms one of the three points of the “summer triangle,” along with Altair and Deneb. From mid-northern latitudes, such as around New York City, Vega can be seen on any night of the year. Go farther north, and the star never sets.
Capella
A dirt road stretches toward the horizon with the star Capella seen directly above it. Jupiter appears as the brightest point at the left. Neal Simpson via Flickr under CC BY-ND 2.0
Derived from the Latin word capra, meaning goat, Capella is known as the “goat star.” It lies 42.8 light-years away in the lesser-known constellation Auriga and sits near a triangle of stars referred to as “the kids,” representing Capella’s celestial offspring.
As evidenced by its distinctive golden hue, Capella is a yellow star, like our own sun—and it’s the brightest yellow star in the night sky.
Though it appears as a single point of light to the naked eye, Capella is a system of four separate stars: two yellow giants named Capella Aa and Capella Ab, as well as two red dwarf stars called Capella H and Capella L.
When Capella first appears in the fall, it’s low on the horizon, causing it to twinkle in fabulous colors, flashing red and green. Capella is also one of the brightest X-ray emission sources in the sky, according to NASA.
How to find Capella: Capella can be seen in the constellation Auriga, the charioteer, between Taurus and Gemini in autumn and winter skies. From the Big Dipper, trace a line away from the handle through the two stars that form the top of the dipper’s bowl, and that will point at Capella. It holds the northernmost spot in the “winter circle” (or “winter hexagon”), a pattern of some of the brightest stars visible during the cold months.
Rigel
Rigel illuminates the Witch Head Nebula in the constellation Orion. NASA / STScI Digitized Sky Survey / Noel Carboni
This relatively young, blue star is the brightest one in the constellation Orion, glowing at the hunter’s left foot. Rigel is the most distant star on this list at about 870 light-years away—so to still appear so bright in our sky, it has to be strong. The star’s powerhouse status comes from the fact that it’s especially hot and energetic—it releases roughly 120,000 times more energy than our sun and is more than twice as hot.
Despite Rigel being much younger than the sun, it is a type of star known as a blue supergiant, which means it has burned through most of the hydrogen in its core and is entering the later part of its life. One day, it will explode as a supernova.
Rigel also illuminates the nearby Witch Head Nebula. The cloud of celestial gas appears blue in part because of the star’s light, but also because its dust grains scatter light in blue wavelengths—just like the molecules in Earth’s atmosphere, which give our daytime sky its cerulean hue.
How to find Rigel: In the constellation Orion, Rigel is at the bottom right from Earth’s perspective, representing the hunter’s left foot. It can be easily seen as the brightest star below the constellation’s characteristic three-star belt.
Procyon
On a foggy night, the three stars of the winter triangle appear in blue—Sirius bright at the center, Rigel in Orion at the right and Procyon shining at the left. Juan Fco. Marrero via Flickr under CC BY-NC-ND 2.0
In large part, Procyon earns its place among the brightest stars in Northern Hemisphere skies because of its proximity to our planet—the two-star system is less than 12 light-years away. Procyon A and its much smaller white dwarf companion, Procyon B, orbit each other and appear as a single point of light to the naked eye, the brightest one in the Canis Minor constellation.
Procyon is also called the “little dog star,” and its name derives from Greek, meaning “before the dog.” This description was a nod to how Procyon rises before Sirius—and while this is still true for many skywatchers, those in the Southern U.S. and at similar latitudes throughout the world now see the stars appear in the opposite order, with Sirius rising first. This shift is a result of Earth’s slow wobbling on its axis, known as precession.
Canis Minor and Canis Major represent Orion’s two hunting dogs, which trail him across winter skies. Canis Minor has only two notable stars bright enough to be seen with the naked eye; alongside Procyon is Gomeisa, which shines at the dog’s neck.
How to find Procyon: Along with Sirius and Betelgeuse, Procyon lies in the “winter triangle.” The bright star sits higher than Sirius in the sky.
Betelgeuse
In an illustration, Betelgeuse, known to be a volatile star, releases a blast of material with 400 billion times the mass of an average coronal mass ejection from our sun, then settles down. NASA, ESA, Elizabeth Wheatley (STScI)
Known as the celestial hunter Orion’s shoulder, the red supergiant Betelgeuse is one of the most recognizable stars in the sky. The huge star is one of the largest known, and though it’s around 700 light-years away, it would stretch past the orbit of Jupiter if placed at the center of our solar system. The aging star appears with an orange tint, even to the naked eye.
Betelgeuse might also be familiar from the news in recent years: Its brightness dropped sharply in 2019—an event termed the “great dimming”—and astronomers thought it might soon explode. While that proved not to be the case, the volatile star has continued to periodically change in brightness—but on the whole, astronomers agree it still has up to 100,000 years of burning left before it goes supernova.
The star’s variable nature has likely persisted for centuries: Despite being the second-brightest star in Orion, Betelgeuse has the Latin name Alpha Orionis—and the “alpha” moniker is reserved for a constellation’s brightest star. This has led to speculation that in 1603, when German astronomer Johann Bayer gave Betelgeuse its Latin name, the star might have shone brighter than Rigel, which out-ranks it on this list today.
How to find Betelgeuse: First, identify the trio of stars that make up Orion’s belt. Imagine a perpendicular line runs through the center star, then follow it up to the bright, red-looking orb above. Betelgeuse is Orion’s right shoulder—on the left side, as seen from Earth—alongside the blue-white star Bellatrix, which forms the hunter’s other shoulder.
Altair
Blue star Altair appears slightly flattened due to its rapid rate of rotation. Pablo Carlos Budassi via Wikimedia Commons under CC BY-SA 4.0
Located about 16.7 light-years away in the eagle constellation, Aquila, the star Altair derives its name from Arabic and means “flying eagle.” On either side of the bright beacon is a dimmer companion; these are called Tarazed and Alshain.
Despite its massive size of roughly 1.6 to 2 times the width of our sun, Altair is known for spinning rapidly. It takes roughly nine to ten hours for the star to complete one rotation, and it turns at a speed about 100 times faster than our sun does. By spinning in this intense way, Altair has become partially flattened, appearing sort of like an M&M—or an egg. This leads to a phenomenon called gravity darkening, in which the star’s poles shine brighter than its equator. The same thing happens to the rapidly spinning Vega.
How to find Altair: Altair is the southernmost of the three bright stars that make up the “summer triangle” pattern and is best seen in the Northern Hemisphere from May through September.
With its characteristic orange glow, Aldebaran is a large star located about 65 light-years away in the constellation Taurus.
If put at the center of our solar system, Aldebaran—with its diameter 44 times that of the sun—would stretch beyond Mercury’s orbit. But the star has a similar mass to our sun, because the gasses within it are much more sparse.
The enormous star might also be host to a gargantuan exoplanet—but astronomers aren’t entirely sure. The theorized world, called Aldebaran b, would be roughly six times the size of Jupiter—and scorching hot. Orbiting such a star might send the planet’s surface temperature up to 2,240 degrees Fahrenheit. Though Aldebaran b’s existence was supposedly confirmed in 2015, a follow-up study in 2019 threw it into question once more.
From our point of view, Aldebaran lies in the ecliptic, or the path along the sky that the sun, moon and planets appear to take. For that reason, these objects periodically approach or cover up the bright star, creating exciting moments for astronomers and astrophotographers.
How to find Aldebaran: Aldebaran is the top-left point of the “V” shape that marks the head of Taurus, the bull. The star represents the celestial ruminant’s eye and is best seen during the winter months, though it will stick around in the sky through mid-May. To find Taurus, begin with the three-star belt of Orion, and follow it to the right—Aldebaran is the next bright star, located between the hunter and the Pleiades star cluster, which can look to the naked eye like a very small version of the Big Dipper.
Antares
The European Southern Observatory’s Very Large Telescope Interferometer captured this detailed image of Antares, released in 2017. ESO / K. Ohnaka
The relatively cool star Antares glows in orange-red—and for this reason, it’s often confused with Mars. But the star’s name—Greek for “rival of Ares” (the counterpart of the Roman god Mars)—makes it clear that this star stands out in its own right.
One of the largest known stars, Antares clocks a diameter around 700 times longer than our sun’s. If put at the center of our solar system, it would swallow up all four of the inner planets—including Mars—and nearly reach the orbit of Jupiter. And that’s only the part of the star seen in visible light—when viewed at radio wavelengths, Antares appears even bigger.
At roughly 600 light-years away, it is a binary system, with a companion star called Antares B, but the light of this smaller star is so dim compared to the main fireball that it takes a very strong telescope to resolve it from the ground.
How to find Antares: Antares is a summer star at the heart of the constellation Scorpius. At northern latitudes, it might appear low in the sky—and above about 63 degrees north, the star never goes above the horizon, so you’ll be out of luck trying to spot it.
Spring Constellations: See a Night Sky Snake, Crow and Goblet
The locations of the constellations Hydra, Corvus (the Crow) and Crater (the Cup) in the southern sky are seen in this sky map provided by Starry Night Software.(Image credit: Starry Night Software)
You wouldn't think that a water snake, a crow and a goblet would have any kind of connection with each other, but all three are tied together in a strange story that spans across the current evening sky.
With the bright moon now completely out of our evening sky, we can look to the south to trace one of the most extensive of all the star patterns: the long, and mostly faint, constellation Hydra, the female water snake.
A male snake bearing the name Hydrus is visible only in Southern Hemisphere sky. One of the more famous Hercules stories is how he killed a hundred-headed serpent known as the Hydra. Perhaps that's why when the constellation of Hercules stands triumphantly overhead on summer evenings, the tail of the constellation Hydra is slithering out of sight below the southwest horizon. [Constellations of the Night Sky: Famous Star Patterns (Images)]
Hydra begins just below the constellation Cancer (the Crab), with a boxy shape of five stars between the bright stars Procyon and Regulus representing the snake's head. Hydra's scraggly stream of dim stars then wriggles southeastward past its lone bright star: the ruddy second magnitude star Alphard, which appears brighter than it actually is because it has no competition. Because of that fact, Alphard is sometimes called the "Solitary One."
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Hydra's long and sinuous trail of dim stars finally ends in a distant tail below the constellation Virgo, and nearly reaches Libra, the Scales, toward the east. The entire snake, running from high in the southwest sky, over toward the south and finally down low to the southeast, is in view this week beginning after about 11 p.m. your local time. Hydra slithers beneath the several other star patterns, including the faint Sextans, the Sextant; Crater, the Cup; and the brighter Corvus, the Crow.
Despite meandering across 95 degrees of the sky (and taking nearly seven hours to fully rise into view), Hydra doesn't include much of general interest to the average skywatcher. One of its stars, Epsilon Hydrae, is actually a multiple star system — a close pair that takes 15.3 years to orbit each other. Yet a third star orbits around the inner pair, and takes about 650 years to make one complete revolution.
Of the three smaller constellations sitting just above Hydra, by far the most conspicuous is Corvus, which on star charts appears as a small, moderately bright quadrilateral-shaped pattern of stars. Were we to add a fainter, adjoining star, the pattern would then resemble the battened mainsail of a Chinese junk, or lugsail, ship.
Unfaithful fowl and a faint goblet
The constellation Corvus is supposed to represent the unfaithful raven of the god Apollo. As the legend goes, the bird was sent out with a goblet or cup for some water, but instead loitered at a fig tree until the fruit became ripe. The crow then returned to Apollo without the cup, but with a water snake in his claws, alleging the snake to be the cause of his delay. [Constellation Quiz: Do You Know Your Star Patterns?]
As punishment, the angry Apollo changed Corvus from a beautiful silvery-white to the black color that all crows and ravens bear to this day. In addition, Corvus was forever fixed in the sky along with the Cup (Crater) and the Snake (Hydra), doomed to everlasting thirst by the guardianship of the Hydra over the Cup and its contents. And this is supposedly why, of all birds, only the raven does not carry water to its fledglings.
Corvus also serves as a useful guide for anyone traveling south. Directly south of Corvus is Crux, the Southern Cross, but one must go well south — down to Brownsville, Texas, or to Miami and the Florida Keys to see this very famous southern constellation.
Crater, the Cup, is a small and rather faint figure, which corresponds quite closely to its name. Its stars indeed outline a goblet, but unfortunately they are hard to distinguish when the sky is hazy or when there is a bright moon in the sky.
And then there is Noctua (Who?)
Lastly, I should mention one other star pattern that can be found on some older star charts sitting complacently on the end of Hydra's tail. It is Noctua, Vel Avis Solitaria, or as it more simply known: the Owl.
Editor's note:If you have an amazing skywatching photo you'd like to share for a possible story or image gallery, please contact managing editor Tariq Malik at spacephotos@space.com.
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for News 12 Westchester, N.Y. Follow us@Spacedotcom,Facebook andGoogle+. Original article onSpace.com.
Want to Go Stargazing? Know the Stars of Early Summer
Just after dark on a June evening, look overhead to see the constellations of early summer: Boötes, Corona Borealis, and Serpens Caput.(Image credit: Starry Night Software)
Early summer is an "in-between" time in the skies. The realm of the galaxies has moved off to the west, but the summer Milky Way has not yet arrived. This is the best time of year to observe globular clusters and double stars.
The centerpiece of the early summer constellations is Boötes, the herdsman, with the bright star Arcturus at his heart. Arcturus is easy to find by following the "arc" of the Big Dipper's handle away from the ladle: it is the only bright star in this part of the sky. Alternately, if you live in the Northern Hemisphere, simply look straight overhead around 11 p.m. your local time.
Although Boötes looks like it might be pronounced like "booties," the diaeresis (double dot) over the second "o" gives you a clue: the two "o"s are pronounced separately: Boh-OO-tes. Its stars form a distinctive kite shape, complete with tail. [The Brightest Stars in the Night Sky]
Arcturus is the third brightest star in the night sky, after Sirius and Canopus. It is relatively close to us, only 37 light-years distant. It is an orange giant star, slightly cooler than the sun, but quite a bit larger in diameter.
These three constellations contain many interesting objects to look at with binoculars or a small telescope. (Image credit: Starry Night Software)
Boötes contains relatively few deep sky objects, but is rich in double and variable stars. Izar (Epsilon Boötis) is one of the finest double stars in the sky. With a separation of only 2.9 arc seconds, it requires at least 3 inches aperture, steady skies, and high magnification to see its duality; its stars are gold and greenish in colour. Alkalurops (Mu Boötis) is a much wider double at 2 arc minutes separation, but it is a challenge to see that one of its stars is itself a double.
Although not within Boötes itself, most amateur astronomers use the stars of Boötes to star-hop to the Messier globular cluster Messier 3 in the dim constellation of Canes Venatici. M3 forms an almost perfect equilateral triangle with Arcturus and Rho Boötis. This is one of the finest globular clusters in the sky.
Just to the left (east) of Boötes is a small circlet of stars forming Corona Borealis, the northern crown. Look within the circle to see if you can see R Corona Borealis, a very unusual variable star. Some have called this an "inverse nova." Most of the time, it shines steadily with a brightness of about magnitude 7, just below naked eye visibility, but easily seen in binoculars. At long and irregular intervals, instead of brightening like a nova, it dims by about 6 magnitudes. This dimming is caused by occasional expulsion of a dark obscuring cloud of dust. Currently R is entering its dark phase, but keep watching, and it should soon reappear.
Below Corona Borealis is one of the most unusual constellations, or rather "half constellations." Serpens represents a snake cut in half, each half held in one hand of Ophiuchus. This is the front half: Serpens Caput, or the head of the serpent. The other half, located quite a ways to the east, is Serpens Cauda, the tail of the Serpent. A triangle is supposed to represent the head of the spent, but I always see this and the two stars above as a large "X."
The brightest star in Serpens bears the ugly name Unukalhai, which is Arabic for "the serpent’s neck." Just above Unukalhai is Delta Serpentis, a fine pair of pale yellow stars in a telescope.
But the real prize in Serpens Caput is the globular cluster Messier 5, every bit as fine as Messier 3 to the northwest. Like all globular clusters, M5 responds well to aperture and magnification. Besides resolving the cluster into myriads of tiny stars, a large telescope will reveal chains of stars and clusters within the cluster.
Milky Way with Nearby Constellations by Matt Dieterich
Here’s an amazing photograph of the Milky Way by astrophotographer Matt Dieterich. He took the image a step further, however, and identified all the constellations you can see close to the Milky Way.
You’ll want to click this image and see a bigger version.
Full panoramic view of the constellations near the Milky Way by Matt Dieterich
Right down near the horizon is Sagittarius – it looks like a teapot, with the Milky Way rising like steam from its spout. Many of the brightest, most spectacular nebulae in the night sky are located around this constellation: the Lagoon Nebula, Trifid Nebula, and the Omega Nebula. The 4 million solar mass supermassive black hole located at the center of the Milky Way is located in this region too.
Further up the Milky Way you can see the three constellations that form the Summer Triangle: Lyra, Cygnus and Aquila.
And right on the left side of the photograph is Cassiopeia, with its familiar “W” shape.
In the lower-right of the image are a few constellations from the zodiac: Scorpio, Libra and Virgo. And if you look closely you can see Saturn making its way across the sky, in the plane of the ecliptic.
If you’re interested in learning about the night sky, I highly recommend you take your time and learn your constellations. These are your wayposts, navigational aides that help you find your way across the Universe, to the wonders right there in the sky above you.
Matt used a Nikon D750 camera with a 24mm f/1.4 lens. The whole image is made up of 20 separate exposures of 15 seconds each, stitched together to make this amazing mosaic. He captured this image from Glacier National Park in Northern Montana.
Here’s the original version, without the highlighted constellations. Once again, you’ll want to click to see the full resolution goodness.
Milky Way (without the constellations) by Matt Dieterich
A big thanks to Matt for contributing this picture to the Universe Today Flickr pool. If you’re an astrophotographer, you’ll be in good company, with thousands of other photographers who share their pictures. We’ve got more than 33,000 pictures there now.
How Low Can You Go? Take the Great Square Challenge
Cast your gaze up, up, up on the next dark, moonless night and stare into the Great Square of Pegasus. How many stars do you see? Zero? Two? Twenty? If you’d like to find out how dark your sky is, read on.
The Great Square, one of the fall sky’s best known star patterns, rides high in the south at nightfall in mid-December. It forms part of the larger figure of Pegasus the Winged Horse. For our purposes today, we’re going to concentrate on what’s inside the square.
Bounded by Alpheratz (officially belonging to adjacent Andromeda), Scheat, Markab and Algenib, the Great Square is about 15° on a side or one-and-a-half balled fists held at arm’s length.
At first glance, the space appears empty, but a closer look from all but the most light polluted skies will reveal a pair 4th magnitude stars in the upper right quadrant of the square. Fourth magnitude is about the viewing limit from a bright suburban location.
Astronomers use the magnitude scale to measure star and planet brightness. Each magnitude is 2.5 times brighter than the one below it. Aldebaran, which shines at 1st magnitude, is 2.5 times brighter than a 2nd magnitude star, which in turn is 2.5 times brighter than a 3rd magnitude star and so on.
Moonlight and especially light pollution reduce the number of stars we can see in the night sky. This specially prepared map shows slices of sky based on amateur astronomer and author John Bortle’s Dark Sky Scale. Classes range from 1 (excellent with stars fainter than 7th magnitude visible) to 9 (inner city with a limiting magnitude of 4). Click for more detailed descriptions of each class and rate your own sky. Credit: International Dark Sky Association
A first magnitude star is 2.5 x 2.5 x 2.5 x 2.5 x 2.5 (about 100) times brighter than a 6th magnitude star. The bigger the magnitude number, the fainter the star. From cities, you might see 3rd magnitude stars if you can block out stray lighting, but a dark country sky will deliver the Holy Grail naked eye limit of magnitude 6. Skywatchers with utterly dark conditions might glimpse stars as faint 7.5. My own personal best is 6.5.
With each drop in magnitude the number of stars you can see increases exponentially. There are only 22 first magnitude or brighter stars compared to 5,946 stars down to magnitude 6.
What appears blank at first is filled with stars — 26 of them down to magnitude 6.3 are visible inside the Great Square from a dark sky site. How many can you see? Click for a larger version. Source: Stellarium
Ready to stretch your sight and rate your night sky? Step outside at nightfall and allow your eyes to dark-adapt for 20 minutes. With a copy of the map (above) in hand, start with the brightest stars and work your way to the faintest. Each every small step down the magnitude ladder prepares your eyes the next.
With a little effort you should be able to spot the four 4th magnitude range stars. At magnitude 5, you’ll work harder. Moving beyond 5.5 can be very challenging. I revert to averted vision to corral these fainties. Instead of staring directly at the star, play your eye around it. Look a bit to this side and that. This allows a rod-rich part of the retina that’s excellent at seeing faint stuff play through the scene and snatch up the faintest possible stars.
Magnitude scale showing the limits of the eye, binoculars and telescopes. Credit: Dr. Michael Bolte, UCO/Lick Observatory
From my house I can pick out about dozen points of light inside the Square on a moonless night. How many will you see? Once you know your magnitude limit, compare your result to John Bortle’s Dark Sky Scale … and weep. No, just kidding. But his Class 1 excellent sky includes a description of seeing stars down to magnitude 8 and the summer Milky Way casting shadows.
Hard to believe that before about 1790, when gas lighting was introduced in England, Class 1 skies were the norm across virtually the entire planet. Nowadays, most of us have to drive a hundred miles or more to experience true, untrammeled darkness.
Have fun with the challenge and let us know in the comments area how you do. Here’s hoping you find the Great Square far from vacant.
Asterisms appeal to our playful side but also serve as key waypoints in the sky for identifying fainter stars and constellations.
There are three asterisms in this photo. Can you find them? Answers at the end of this article. Bob King
Thank goodness for asterisms! If you're a beginning skywatcher, asterisms ease your entry into the night sky. Even seasoned observers know that most constellations don't look like the figures they're supposed to represent. OK, some do. Like Ursa Major, the Great Bear, or Delphinus, the Dolphin. But you'll pull your hair out trying to see a chained princess in Andromeda or the chariot-driving Auriga.
Asterisms are easy-to-recognize patterns that can be part of a larger constellation or composed of stars from more than one constellation. One of the biggest, the Winter Hexagon, borrows from six! Some asterisms even involve the entire constellation, as in the 'W' of Cassiopeia or the Northern Cross, a.k.a. Cygnus, the Swan.
All asterisms have one thing in common: they make wonderful places from which to begin learning the constellations.
A great many skywatchers have cut their teeth on Orion's Belt (yours truly) and the Big Dipper, straightforward, easy-to-recognize patterns of relatively bright stars. Finding the Belt is your passport to the rest of the great hunter.
Two familiar asterisms of fall and winter are the Great Square of Pegasus and the faint Circlet of Pisces. Both are visible in the southwestern sky during early evening hours in mid-January. Bob King
From the Dipper, we can use the Pointer Stars (another asterism) to arrive at the North Star or explore the very bear-like outline of the constellation Ursa Major. While we're talking about the Belt, Aussie skywatchers, who see Orion upside-down from our northern perspective, picture a "saucepan" by combining the Belt with Orion's Sword. Since Orion is very much a summertime constellation viewed from down under, could homemade barbecue sauce be bubbling away in there, I wonder?
Find the Great Square of Pegasus and you’ll be on your way to identifying six key stars that head up six different constellations. Stellarium
The Sickle of Leo asterism works backwards and forwards, west to faint Cancer the Crab and the Beehive Cluster and east to the lion's tail. Shooting lines through the Great Square of Pegasus, a favorite fall asterism, plunges our gaze into the watery depths where we meet up with Piscis Austrinus, the Southern Fish, and the gargantuan Cetus, the Sea Monster.
Can you see the Hexagon and the letter G? From bottom clockwise: Sirius, Procyon, Pollux, Castor, Capella (overhead), Aldebaran and Rigel. Betelgeuse is a lone horse corralled by the figure. Bob King
For sentimental reasons, Orion's Belt will always be my favorite, but no pattern connects more bright stars and offers avenues to a greater diversity of constellations than the Winter Hexagon. First-time skywatchers are wowed by the Hexagon's sheer size . . . and its brilliance.
From Capella to Sirius, top to bottom, the figure spans 65°, or more than six fists at arm's length, and 45° in width (Procyon to Aldebaran). Here's the kicker: Not only does it vie for biggest asterism in the known universe, it contains 7 of the sky's 21 first magnitude or brighter stars: Sirius, Procyon, Pollux, Capella, Aldebaran, Rigel, and Betelgeuse.
A word about Pollux's neighbor Castor. At magnitude 1.6, it's officially a 2nd-magnitude star, but situated so close to the figure, it doesn't seem right to exclude it. If we graciously include Castor, the Hexagon morphs into a 7-sided Heptagon.
Betelgeuse, sadly left out of all the geometric merrymaking, comes into its own in the Heavenly G, completing the letter's inner lobe. Whatever form you prefer, the best time to view it is around 9 to 11 p.m. in mid-January as it stands high (and low) in the south-southeastern sky.
Start with the unmistakably brilliant Sirius at the lowest apex and work your way clockwise and up to Procyon in Canis Minor, the Gemini Twins, the neck-cracking Capella near the zenith, then down to Aldebaran, and farther to sparkling, white Rigel in Orion. Swirl your gaze around it a few times for the full effect.
Winter Hexagon or Heptagon — your choice. To better sense the depth of the scene, I've added each star's distance from Earth. The winter Milky Way "flows" directly through the grand figure. See a video about the future of the Hexagon from Sky & Telescope's Tony Flanders. Stellarium
Now, imagine if you're new to the sky how helpful this asterism will be. Using these 6 or 7 stars you can pilot to a half-dozen constellations or more. What a great way to learn the sky — establish a base of operations from which to make nightly forays into lesser known realms.
The southern sky asterism the "Saucepan", composed of Orion's Belt, Sword and the star Saiph. Stellarium
One final asterism of winter nights is far less showy but no less amazing — the Three Leaps of the Gazelle. You'll spot it springing alongside the Big Dipper in the northeastern sky from about 9 o'clock on.
This is an ancient Arabic star group composed of three sets of paired stars that resemble starry hoof prints in the sky. None of the pairs is especially bright, but the six stars are stand-outs because they form a striking repetitive pattern. All of them belong to Ursa Major.
Legend has it that the gazelle was startled by the lion as it drank from a pond (Coma Berenices) near the lion’s lair. It sprang up and leaped across the sky from east (left) to west, leaving impressions in muddy ground. Here’s the breakdown on the stars’ names, which refers to the first, second, and third leap respectively from east to west:
* First Leap — Alula Australis (Nu UMa) and Alula Borealis (Xi UMa) * Second Leap — Tania Australis (Lambda UMa) and Tania Borealis (Mu UMa) * Third Leap — Talitha (Iota UMa) and Kappa UMa
Three asterisms revealed! The pale green and red banding is airglow. Bob King
Lots of skywatchers like making their own asterisms. Amateur astronomer Greg Furtman of Webster, Wisconsin, sees a stone skipping on water in a long arc of stars beginning with the "throwing arm" of the Big Dipper's Handle and ending half a sky later in southern Ophiuchus. And anyone who's used a telescope or finderscope to star-hop to a favorite deep sky object creates one temporary asterism after another to navigate their way from point A to the target.
Let me guess. You've probably created a few asterisms of your own. If you have, we'd love to hear from you. Just share your pattern in the comments section. Asterisms — they're everywhere!
The imaginative Skipping Stones asterism follows a rock's progress from the "throwing arm" of the Big Dipper south all the way to 35 Ophiuchi. Each stellar pair or single star is a skip of the rock on a heavenly sea. Stellarium
Winter Constellations: Orion the Hunter Reigns in Cold Night Sky
Astronaut Karen Nyberg tweeted a photo of the constellation Orion taken aboard the International Space Station. Tweet dated August 15, 2013.(Image credit: Karen L. Nyberg (via Twitter as @AstroKarenN))
Every summer in mid-August, when I'm stretched out on a long lawn chair in the predawn hours scanning the skies for Perseid meteors, I'll always pause before the break of dawn to watch for Orion the Hunter's rise in the sky.
At that time of the year the nights are balmy and even in the early hours of the morning you rarely need more than a sweater or light jacket to stay comfortably warm. Seeing the constellation Orion emerging from beyond the eastern horizon at that warm time of the year is a signal that we are turning the corner meteorologically speaking, and that soon the nights will be growing progressively chillier.
By the turn of the year, when the air flow is streaming south from northern Canada and nights have turned decidedly cold (as most of us who have recently experienced the effects of the polar vortex can attest), the Hunter will hold forth as a majestic figure high in the winter sky. [See amazing photos of the Orion Nebula]
On winter evenings, Orion dominates the sky, surrounded by numerous striking constellations, all decorated with brilliant stars. (Image credit: Starry Night Software)
Like celestial jewelry
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Astronomer Robert H. Baker (1880-1962) once wrote that Orion shines "like a gigantic piece of celestial jewelry through the frosty winter air." [Night Sky Constellations Explained (Images)]
Indeed, Orion is by far, the most brilliant of the constellations and is visible from every inhabited part of the Earth. As darkness descends this month, Orion clearly dominates the southeast sky. Three bright stars decorate Orion's belt, which points northward to the Hyades and Pleiades star clusters of Taurus, and southward to the Dog Star Sirius.
Within Orion we find two immense stars, Rigel and Betelgeuse, representing two entirely different periods of a star's life.
Opposite sides of the spectrum
Rigel is a star reaching the prime of its life. It's a true supergiant: a blazing white-hot star of intense brilliance and dazzling beauty. Located 860 light-years from Earth, its computed luminosity is roughly 130,000 times the brightness of the sun. It ranks as the seventh brightest star in the night sky at magnitude +0.12.
Betelgeuse, by contrast, shines with a cool, dull ruddy hue and is located 643 light-years away. It is an irregular pulsating supergiant star, nearing the end of its life. It is expected to become a supernova sometime within the next million years according to scientists, and as such it expands and contracts spasmodically.
Incredibly, Betelgeuse's diameter can vary between 550 to 920 times the diameter of our sun. If it were possible to shrink the sun down to the size of a baseball, Betelgeuse could be represented by a balloon ranging in size from 100 to 176 feet (30 to 54 meters) across. Starting in 1993 and continuing for at least 15 years, its radius shrank by 15 percent, an astonishing amount for so short a time.
"We do not know why the star is shrinking," Edward Wishnow, a research physicist at UC Berkeley's Space Sciences Laboratory, said in 2009. "Considering all that we know about galaxies and the distant universe, there are still lots of things we don't know about stars, including what happens as red giants near the ends of their lives." [Spectacular Night Sky Photos by Stargazers: January 2014]
As a consequence of this shrinking and swelling, it has a variable brightness generally peaking as bright as 0.0 and appearing as dim as +1.3. In 1933 and again in 1942, it shone as bright as magnitude +0.2 making it brighter than Rigel. Its average magnitude of +0.45 ranks it as the ninth brightest star in the night sky.
As is also the case with the mighty Hercules, the figure of Orion has been associated in virtually all-ancient cultures with great national heroes, warriors, or demigods. Yet, in contrast to Hercules, who was credited with a detailed series of exploits, Orion is more of a vague and shadowy figure.
The ancient mythological stories of Orion are so many and so confused that it is almost impossible to choose among all of tem. Even the origin of the name Orion is obscure, though some scholars have suggested a connection with the Greek "Arion," meaning simply warrior. All, however, agree that he was the mightiest hunter in the world and is always pictured in the stars with his club upraised in his right hand.
Hanging from his upraised left hand is the skin of a great lion he has killed and which he is brandishing in the face of Taurus, who is charging down upon him.
Stellar incubator
Below Orion's three-star belt is undoubtedly one of the most wonderfully beautiful objects in the sky: the great Orion Nebula. It appears to surround the middle star of a fainter trio of stars in a line that marks the hunter's sword.
The nebula is invisible to the unaided eye, though the star itself appears a bit fuzzy. It can be seen in good binoculars and small telescopes as a bright gray-green mist enveloping the star. In larger telescopes it appears as a great glowing irregular cloud. The nebula emits a glow produced by fluorescence from the strong ultraviolet radiation of four hot stars entangled within it.
Edward Emerson Barnard (1857-1923), for many years an astronomer at Yerkes Observatory, once remarked that it reminded him of a great ghostly bat, and he always experienced a feeling of surprise when he saw it.
The Orion Nebula is a vast cloud of extremely tenuous glowing gas and dust, approximately 1,300 light-years away. The nebula is about 24 light-years across (or more than 20,000 times the diameter of the entire Solar System). Astrophysicists now believe that this nebulous stuff is a stellar incubator; the primeval chaos from which star formation is presently underway.
Editor's Note: If you snap an amazing night-sky photo and would like to share it with SPACE.com for a possible story or gallery, please send images and comments (including your name and the photo's location) to managing editor Tariq Malik at: spacephotos@space.com.
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for News 12 Westchester, N.Y.Follow us @Spacedotcom, Facebook and Google+. Original article on SPACE.com.
Article Updated: 16 Oct , 2016 
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