Constellation Atlas: Who is Who in the Night Sky

Ursa Major (the Great Bear)

Ursa Major

How to find it. Look for seven bright stars in the shape of a ladle: four make the bowl, three the handle. That is the Big Dipper (the Plough), the best-known part of Ursa Major. The constellation itself is much larger, but the rest is made of fainter stars. From here the Dipper never sets; it only wheels around Polaris through the year.

Brightest star

Alioth ε UMa · magnitude 1.8 · 83 light-years
a white star, third from the end of the handle

What to look for

Mizar and Alcor
The middle star of the handle is Mizar. Right beside it, about 12 arcminutes away, sits fainter Alcor. If you can split them with the naked eye, your eyesight is fine: the ancient Arabs and Persians already used them as a vision test. In binoculars the pair is beautifully clear.

What we know

The five middle stars of the Big Dipper travel through space together, as one loose group. The end stars, Dubhe and Alkaid, do not belong to it and are heading elsewhere. So the Dipper is slowly but surely coming apart.

Ursa Minor (the Little Bear)

Ursa Minor

How to find it. Find the outer wall of the Big Dipper’s bowl, the stars Merak and Dubhe. Extend the line from Merak through Dubhe about five times and you arrive at Polaris. It marks the end of the Little Dipper’s handle. The other stars are faint, so in town you often see only Polaris and the two stars at the far end.

Brightest star

Polaris α UMi · magnitude 2 · 447 light-years
a yellow supergiant and a pulsating star, a Cepheid An older Hipparcos measurement gave about 432 light-years.

What to look for

The Guardians of the Pole and a darkness test
Kochab and Pherkad at the end of the bowl are called the Guardians of the Pole. The four bowl stars range from 2nd to 5th magnitude, so they work as a darkness gauge. Can you see all four? You are in a good spot. Only two? There is too much light around you.

What we know

Polaris is not the brightest star in the sky. It matters because of where it is: less than one degree from the north celestial pole, so it stays almost still all night. It is also a Cepheid whose brightness changes slightly in a rhythm of about four days.

Where the name comes from. Phoenician sailors are said to have steered by this constellation.

Cassiopeia

Cassiopeia

How to find it. Five bright stars in the shape of a W, or an M, depending on which way up it is. It lies on the opposite side of Polaris from the Big Dipper: when the Dipper is low, Cassiopeia is high. On autumn evenings it is almost overhead.

Brightest star

Schedar α Cas · magnitude 2.2 · 228 light-years
one of the five stars of the W; the middle one, Gamma Cas, sometimes outshines it

What to look for

The Owl Cluster (NGC 457)
An open cluster of more than a hundred stars, about 10,000 light-years away. In binoculars it is a small hazy tuft not far from the star Ruchbah. And while the binoculars are in your hand, sweep slowly across all of Cassiopeia: it lies in the Milky Way and there are stars beyond counting.

What we know

In 1572 a supernova flared up here and was observed by Tycho Brahe. You will not find it with the naked eye any more, but its remnant still gives off radio waves. The middle star of the W, Gamma Cas, is an unpredictable variable star.

Where the name comes from. A queen who boasted about her beauty for so long that she angered the god of the sea.

Cepheus

Cepheus

How to find it. A little house with a pointed roof, the kind children draw. Look for it between Cassiopeia, Draco and Cygnus. Its stars are fainter than its neighbours’, so in town it takes some effort.

Brightest star

Alderamin α Cep · magnitude 2.5 · 49 light-years
a white star that spins once in under 12 hours

What to look for

The Garnet Star (Mu Cephei)
One of the reddest stars you will see. Its brightness wanders between magnitude 3.4 and 5.1, so sometimes you can find it with the naked eye and sometimes you need binoculars. That is where the colour looks best. It is a supergiant so large that, put in the Sun’s place, it would reach somewhere beyond the orbit of Jupiter.

What we know

Delta Cephei gave its name to a whole class of stars, the Cepheids. Its brightness varies between magnitude 3.5 and 4.4 with a period of 5 days and 9 hours, as John Goodricke noticed in 1784. In Cepheids the length of the period is tied to the true luminosity, which is how astronomers use them to measure distances in space.

Where the name comes from. A king, husband of Cassiopeia and father of Andromeda. The whole family has seats next to each other in the sky.

Draco (the Dragon)

Draco

How to find it. A long, winding chain of fainter stars that snakes between the Big and Little Dippers. The head is easiest to find: a small quadrilateral not far from Hercules and bright Vega. From there, follow the body back towards the Dippers.

Brightest star

Eltanin γ Dra · magnitude 2.2 · 148 light-years
an orange giant in the dragon’s head

What to look for

The double star Nu Draconis
The faintest star in the dragon’s head. Point binoculars at it and it splits into two equally bright white stars, both of magnitude 4.9. They look like a pair of eyes watching you from the dark.

What we know

The Earth’s axis slowly wobbles, so Polaris has not always been the pole star. Roughly between 3900 and 1800 BC, north was marked by Thuban in Draco. And it was on Eltanin that James Bradley discovered the aberration of light in 1728, one of the first direct proofs that the Earth moves.

Where the name comes from. The dragon Ladon, who guarded the golden apples of the Hesperides until Heracles turned up.

Leo (the Lion)

Leo

How to find it. Go back to the bowl of the Big Dipper. A line from Megrez through Phecda, that is through the bottom of the bowl and away from Polaris, takes you to Regulus. Above it are six stars shaped like a backwards question mark: the Sickle, the lion’s head and mane.

Brightest star

Regulus α Leo · magnitude 1.4 · 79 light-years
a blue-white star, in reality a system of at least four stars

What to look for

The Sickle and the Leonids
The Sickle is made of Regulus, Algieba and four more stars, and you can recognise it even from a town. In mid-November the Leonid meteors seem to fly out of it; their radiant lies near Algieba. In an ordinary year only about ten fall per hour, so patience counts.

What we know

Regulus spins once in just under 16 hours, where the Sun takes about 25 days. It turns so fast that it is noticeably flattened and only a little short of the speed at which it would start to tear apart. It lies right beside the ecliptic, so from time to time the Moon passes in front of it.

Where the name comes from. The Nemean lion, which Heracles overcame as the first of his twelve labours.

Boötes (the Herdsman)

Boötes

How to find it. Extend the curve of the Big Dipper’s handle, from Alioth through Mizar and Alkaid and onwards. The first really bright star you meet is orange Arcturus. The rest of the constellation above it looks like a kite or an ice-cream cone.

Brightest star

Arcturus α Boo · magnitude -0.05 · 37 light-years
an orange giant, the fourth-brightest star in the night sky

What to look for

The colour of Arcturus
Stars are not just white dots. Look at Arcturus and then at any star of the Big Dipper: Arcturus is plainly orange. Put your binoculars slightly out of focus and the colour stands out even more.

What we know

Arcturus is the brightest star in the northern half of the sky. Its mass is similar to the Sun’s, but it is older and has already swollen to about 25 times the Sun’s radius. It shines about 170 times more strongly. This is roughly what our own Sun will look like one day.

Where the name comes from. The name Arcturus is Greek for Guardian of the Bear: in the sky it faithfully follows Ursa Major.

Virgo

Virgo

How to find it. The curve of the Big Dipper’s handle took you to Arcturus. Keep following the same curve and, lower above the horizon, you find a lonely blue-white star: Spica. Follow the arc to Arcturus, then speed on to Spica. The other stars of Virgo are faint and scattered over a large area; it is the second-largest constellation in the sky.

Brightest star

Spica α Vir · magnitude 1 · 250 light-years
a close pair of hot blue stars

What to look for

Spica against Arcturus
Two bright stars on one arc, each a different colour. Spica is blue-white, Arcturus orange. The colour gives away the surface temperature: blue stars are hotter than orange ones, exactly the opposite of a bathroom tap.

What we know

When you look into Virgo you are looking out of our Galaxy. This is where the Virgo Cluster lies: 1,300 to 2,000 galaxies roughly 54 million light-years away. You will not see them in binoculars, but it is good to know they are there.

Where the name comes from. The Greeks and Romans saw in it Demeter, goddess of the harvest, or Astraea, goddess of justice.

Cygnus (the Swan)

Cygnus

How to find it. On summer evenings look high up for three bright stars in a huge triangle: Vega, Deneb and Altair. Deneb is the Swan’s tail. From it a long cross runs along the Milky Way to the star Albireo, which is the head. That is why the constellation is also called the Northern Cross.

Brightest star

Deneb α Cyg · magnitude 1.25 · 2,600 light-years
a white supergiant, one of the most luminous stars of its kind

What to look for

Albireo
To the naked eye, one star in the Swan’s head. A small telescope splits it into two, amber and blue-green, 35 arcseconds apart. It is one of the finest colour-contrast double stars in the sky. With larger binoculars braced against something solid you can try to split it yourself. Whether the two really orbit each other is still not known.

What we know

Cygnus holds Cygnus X-1, the first X-ray source widely accepted to be a black hole. It pulls in matter from a companion star. And in 1838 the star 61 Cygni became the first to have its distance measured, by Friedrich Bessel.

Lyra (the Lyre)

Lyra

How to find it. The brightest star of the Summer Triangle is Vega, almost overhead on summer evenings. Right beside it hangs a small parallelogram of four fainter stars. That is all of Lyra: a small constellation with a big star.

Brightest star

Vega α Lyr · magnitude 0.03 · 25 light-years
a white star, the fifth-brightest in the night sky

What to look for

Epsilon Lyrae, the Double Double
A faint star right next to Vega. Binoculars easily split it into two, about 3.5 arcminutes apart. In excellent conditions a sharp eye can do it unaided. And a larger telescope shows that each of them is double again. Four stars in one point.

What we know

Vega was the first star after the Sun ever to be photographed: on 17 July 1850 at Harvard College Observatory. About 14,000 years ago it was the pole star, and in roughly 12,000 years it will be again.

Where the name comes from. The lyre of the singer Orpheus, whose music was said to move even rocks.

Aquila (the Eagle)

Aquila

How to find it. Altair is the lower, southern corner of the Summer Triangle. You can tell it by the two fainter stars on either side, Tarazed and Alshain, which make a short straight line with it. The Eagle flies along the Milky Way, towards the Swan.

Brightest star

Altair α Aql · magnitude 0.76 · 17 light-years
a white star, one of the nearest visible to the naked eye

What to look for

The Summer Triangle
Vega, Deneb and Altair do not make a constellation, but they are the best signpost in the summer sky. In late June you find the triangle in the east in the evening, later in summer high overhead. The interesting part is what you cannot see when you look at it: Altair is 17 light-years away, Vega 25 and Deneb around 2,600.

What we know

Altair spins once in less than eight hours. The spin has stretched it so much that it is more than a fifth wider at the equator than at the poles. It is less a sphere than a slightly squashed ball.

Where the name comes from. The eagle that carried Zeus’s thunderbolts.

Scorpius (the Scorpion)

Scorpius

How to find it. On June and July evenings look low above the southern horizon. The reddish, strongly twinkling star is Antares. To its right, three stars of the claws stand almost vertically above one another. You need a clear view to the south: from here we see mainly the upper part of the constellation, while the tail and sting stay at the horizon or below it.

Brightest star

Antares α Sco · magnitude 1 · 550 light-years
a red supergiant The brightness of Antares slowly varies between magnitude 0.6 and 1.6.

What to look for

Antares low above the horizon
Your eyes are enough. Antares has a colour you rarely find in the sky, and because it is low, the thick layer of air makes it flicker through every shade. If Mars happens to be nearby, compare them: they are alike in colour and brightness.

What we know

Antares has a radius roughly 680 times that of the Sun. If it stood in the Sun’s place, it would reach somewhere into the asteroid belt beyond the orbit of Mars. It also has a blue-white companion, though you will not see that without a telescope.

Where the name comes from. The name Antares means rival of Ares, that is of Mars, because of the similar red colour.

Sagittarius (the Archer)

Sagittarius

How to find it. To the left, that is east of Scorpius, just as low above the southern horizon. Do not look for an archer. Eight stars make a far clearer figure: a teapot with a lid, a handle and a spout. You see it best in July and August from a place with a dark southern sky.

Brightest star

Kaus Australis ε Sgr · magnitude 1.85 · 140 light-years
a blue-white giant at the base of the Teapot

What to look for

The Lagoon Nebula (M8)
A cloud of glowing gas about 5,200 light-years away, a little above the Teapot’s spout. Under a dark sky it is faintly visible to the naked eye; in binoculars it is a distinct misty patch. From here it is low, so wait for a night when the air is clear right down to the horizon.

What we know

In this direction lies the centre of our Galaxy, about 27,000 light-years away. It is home to the black hole Sagittarius A*, with the mass of four million Suns. Astronomers published the first image of it on 12 May 2022. That is why the Milky Way is densest and brightest right here.

Where the name comes from. The Babylonians already saw a centaur-like creature here, shooting a bow.

Hercules

Hercules

How to find it. From Vega set off towards Arcturus. About a third of the way along you find four modest stars in a slightly lopsided square, known as the Keystone. That is the torso of Hercules. A big constellation, the fifth-largest in the sky, but without a single really bright star.

Brightest star

Kornephoros β Her · magnitude 2.8 · 148 light-years
a yellow giant

What to look for

The globular cluster M13
It lies on one side of the Keystone, between the stars Eta and Zeta Herculis. In binoculars it looks like a blurred star that refuses to focus. In reality it is hundreds of thousands of stars packed into a ball about 25,000 light-years away. On a very dark night it can be glimpsed without binoculars.

What we know

On 16 November 1974 scientists used the Arecibo radio telescope to send a message for any listeners towards M13. It will travel for at least 25,000 years. So we shall be waiting a while for the reply.

Where the name comes from. The earliest Greeks did not know Hercules here, only a figure they called the Kneeler.

Pegasus

Pegasus

How to find it. On autumn evenings look high in the south for a large, almost empty square of four similarly bright stars. That is the Great Square of Pegasus. One of its corners, Alpheratz, officially belongs to neighbouring Andromeda.

Brightest star

Enif ε Peg · magnitude 2.4 · 690 light-years
an orange supergiant, the winged horse’s nose

What to look for

The globular cluster M15
About four degrees from Enif, to the west-northwest. In binoculars it is a small fuzzy star. Its light has travelled for more than 30,000 years, and the cluster itself is one of the oldest known: around 12 billion years old.

What we know

Around the star 51 Pegasi, Michel Mayor and Didier Queloz discovered in 1995 the first planet orbiting a Sun-like star. Until then the only planets we knew were those of our own solar system.

Where the name comes from. The winged horse that helped the hero Bellerophon defeat the Chimera.

Andromeda

Andromeda

How to find it. Start at the corner of the Great Square, at the star Alpheratz. From there a chain of bright stars runs off towards Cassiopeia and Perseus: Alpheratz, Mirach, Almach. That is Andromeda.

Brightest star

Alpheratz α And · magnitude 2.1 · 97 light-years
a blue-white binary; Mirach is almost equally bright

What to look for

The Andromeda Galaxy (M31)
From Mirach go at right angles to the chain to the fainter star Mu Andromedae, then carry on as far again. Under a dark sky you will see a faint elongated smudge there with the naked eye. In binoculars it is brighter, with a concentrated centre. It is a galaxy 2.5 million light-years away, six times wider in the sky than the full Moon. All you see of it is the bright core.

What we know

M31 is the most distant thing the human eye can see unaided. The light landing on your retina set out 2.5 million years ago. The first known record of it was written by the Persian astronomer al-Sufi in 964.

Where the name comes from. A princess chained to a rock as a sacrifice to a sea monster; Perseus rescued her.

Perseus

Perseus

How to find it. Below Cassiopeia, between it and bright Capella. Look for an arc of stars with Mirfak, the brightest, in the middle. It lies in the Milky Way, so in binoculars there is always something to look at.

Brightest star

Mirfak α Per · magnitude 1.8 · 510 light-years
a yellow-white supergiant in the middle of its own star cluster Sources give 510 to 590 light-years.

What to look for

The Double Cluster (h and Chi Persei)
Halfway between Perseus and Cassiopeia. To the naked eye it is a misty little patch, which Hipparchus already recorded as a patch of light around 130 BC. Binoculars show that it is two star clusters side by side. They are about 7,500 light-years away and, by stellar standards, very young: around 14 million years.

What we know

Every 2.867 days, that is once in just under three days, Algol noticeably fades for a few hours: from magnitude 2.3 to 3.5. It is not pulsating. It is two stars orbiting each other, the fainter regularly passing in front of the brighter. You can see the change without any instrument.

Where the name comes from. The name Algol comes from the Arabic Ra’s al-Ghul, the Demon’s Head. Somebody noticed that winking a long time ago.

Orion

Orion

How to find it. The easiest constellation of winter. Four bright stars make a large rectangle and in the middle of it are three stars in a tight row: Orion’s Belt. Orange Betelgeuse shines at the top left, blue-white Rigel at the bottom right.

Brightest star

Rigel β Ori · magnitude 0.13 · 860 light-years
a blue supergiant

What to look for

The Orion Nebula (M42)
Below the Belt hangs a short vertical row of fainter stars, Orion’s Sword. The middle one is not a star: even to the naked eye it looks slightly blurred. In binoculars it is a greyish little cloud. You are looking at a cloud of gas about 1,500 light-years away in which new stars are being born right now. It is the nearest large stellar nursery.

What we know

At the turn of 2019 and 2020 Betelgeuse faded so much that people noticed with the naked eye. It did not become a supernova. The star had thrown off a bubble of gas, part of its surface cooled, and the gas turned into dust that shaded it for a while. By April 2020 it was shining as before.

Where the name comes from. A giant hunter from Greek myth; people have seen his belt and sword here for thousands of years.

Taurus (the Bull)

Taurus

How to find it. Extend Orion’s Belt up and to the right. It leads you to orange Aldebaran, which sits at the end of a letter V made of stars. Those are the Hyades, the bull’s head. Carry on further in the same direction and you come to a small glittering knot: the Pleiades.

Brightest star

Aldebaran α Tau · magnitude 0.86 · 65 light-years
an orange giant, the bull’s eye

What to look for

The Pleiades (M45)
To the naked eye, a tiny dipper of six or seven stars, which is why they are also called the Seven Sisters. Binoculars show dozens, and it is one of the loveliest views the sky has to offer. The whole cluster has over a thousand stars and is roughly 445 light-years away.

What we know

Aldebaran looks like part of the Hyades, but it does not belong to them. It is 65 light-years from us, the cluster 153. It just happens to lie in the same direction. The Hyades, for their part, are the nearest open cluster of all.

Where the name comes from. The white bull into which Zeus changed himself to carry off the princess Europa.

Gemini (the Twins)

Gemini

How to find it. In Orion, join Rigel to Betelgeuse and extend the line. It leads you to two bright stars close together: Castor and Pollux, the heads of the twins. Their bodies are two rows of fainter stars pointing back towards Orion.

Brightest star

Pollux β Gem · magnitude 1.14 · 34 light-years
an orange giant with a planet of its own

What to look for

The star cluster M35
At Castor’s foot, at the end of one of the rows. On a very dark night it is a vague fuzzy spot to the naked eye. In binoculars it becomes a haze in which you can pick out individual stars. It is about 2,800 light-years away.

What we know

Pollux is brighter than Castor, even though Castor carries the designation alpha. When Johann Bayer handed out the letters in 1603, he did not check very carefully which of the pair shines more strongly. Castor makes up for it another way: it is really six stars orbiting one another.

Where the name comes from. The twins Castor and Pollux; when mortal Castor died, Zeus united them in the sky.

Canis Major (the Great Dog)

Canis Major

How to find it. Extend Orion’s Belt the opposite way from Taurus, down and to the left. You cannot miss it: Sirius is the brightest star in the night sky. From here it stands low in the south, which is why it flickers and changes colour so wildly.

Brightest star

Sirius α CMa · magnitude -1.46 · 8.6 light-years
a white star with a white-dwarf companion

What to look for

The star cluster M41
About four degrees below Sirius, so roughly in the same binocular field. An open cluster as large in the sky as the full Moon, around 2,300 light-years away. From here it is low, so you need a transparent night and a clear view south.

What we know

Sirius has a companion that was calculated first and seen only later. In 1844 Friedrich Bessel concluded from the wobble in Sirius’s motion that an invisible body was orbiting it. In January 1862 Alvan Graham Clark spotted it while testing a new telescope. Sirius B is a white dwarf and circles Sirius once every 50 years.

Where the name comes from. The name Sirius comes from the Greek word for glowing or scorching.

Auriga (the Charioteer)

Auriga

How to find it. On winter evenings Capella is a bright yellowish star almost overhead. Around it is a large pentagon whose bottom corner, Elnath, is shared with Taurus. At other times of year the Big Dipper helps: a line across the top of the bowl from Megrez to Dubhe points to Capella.

Brightest star

Capella α Aur · magnitude 0.08 · 43 light-years
two yellow giants plus a pair of red dwarfs

What to look for

The star clusters M36, M37 and M38
Three open clusters inside Auriga’s pentagon and right beside it. In binoculars they are three small misty patches; M37 is the brightest. Each is around 4,000 light-years away. Finding all three in one evening is a nice warm-up task.

What we know

Capella looks like one star but is four: two yellow giants close together and, some way off, a pair of red dwarfs. It is the sixth-brightest star in the night sky. And from our latitudes it never sets; in summer it just scrapes along above the northern horizon.

Where the name comes from. The Arabs called Capella the goat; the two faint stars below it are still known as the Kids.