What is a constellation? Star patterns and the 88 constellations, explained
By the WhyCosmos team · Last updated:
A constellation is a named pattern of stars and, officially, one of 88 regions that together cover the whole sky, as defined by the International Astronomical Union. The stars in a constellation only look close together from Earth; most lie at very different distances. People have used constellations for thousands of years to map the sky, navigate and tell stories.
Long before maps and phones, people found their way and tracked the seasons by the stars, and constellations were how they remembered them. Many Indian families already know a few without realising it: Saptarishi is the pattern called the Big Dipper in English, and Dhruva Tara is the Pole Star. This page explains what a constellation really is, how many there are, and which ones a child can find tonight.
How to explain it to your child
Explain it to an 8-year-old
Imagine a page covered in dots. If you draw lines between some of them, you might see a person, an animal or a ladle. People did the same thing with the stars thousands of years ago, and gave the pictures names, like Orion the hunter or Saptarishi, the seven sages. Those star pictures are constellations.
Explain it to a 13-year-old
Modern astronomy divides the whole sky into 88 constellations with official boundaries, like countries on a map, so every star belongs to exactly one. The bright stars that form each familiar pattern look side by side only from our viewpoint; in three dimensions they can be hundreds of light-years apart. As Earth orbits the Sun, our night side faces different directions in space, which is why different constellations are visible in different seasons.
Key facts
| Official constellations | 88, adopted by the International Astronomical Union in 1922 |
|---|---|
| Official boundaries | Fixed by the IAU in 1928 |
| Largest | Hydra, the water snake |
| Smallest | Crux, the Southern Cross |
| Big Dipper (Saptarishi) | An asterism, a pattern inside the constellation Ursa Major, not a constellation itself |
| Pole Star (Dhruva Tara) | Polaris, in the constellation Ursa Minor |
| Why they change with the seasons | Earth's orbit around the Sun |
| Are the stars really together? | Usually not; they only line up from our viewpoint |
Are the stars in a constellation really close together?
Usually not. Two stars can look side by side from Earth even if one is far behind the other. In Orion, red Betelgeuse and blue-white Rigel look like partners in the same figure, yet Rigel is roughly 860 light-years away and Betelgeuse roughly 550 to 720, so Rigel is well over a hundred light-years farther from us. The pattern exists only because of the direction we happen to be looking from.
If we could travel far across the galaxy and look back, almost every familiar constellation would have a completely different shape, or would not look like a pattern at all.
Which constellations are easiest to find from India?
| Constellation | How to spot it | Best evenings |
|---|---|---|
| Orion, the hunter | Three bright stars in a short straight line, Orion's Belt, between red Betelgeuse and blue-white Rigel | December to March |
| Ursa Major (with Saptarishi) | Seven bright stars shaped like a ladle or a question mark, in the northern sky | March to June |
| Leo, the lion | A backwards question mark of stars, the Sickle, ending at bright Regulus | March to May |
| Scorpius, the scorpion | A long curved hook of stars with red Antares at its heart, in the south | May to August |
| Cassiopeia | A W or M shape of five stars, on the opposite side of the Pole Star from the Big Dipper | October to December |
The two stars at the end of Saptarishi's ladle point to Dhruva Tara, the Pole Star. Its height above the northern horizon roughly equals your latitude, so it sits low, about 13 degrees up in Chennai and about 29 degrees up in Delhi. Navigators used exactly this to work out how far north they were. A free app such as Stellarium helps children learn the patterns on screen before trying outdoors.
What is the difference between a constellation and an asterism?
A constellation is one of the 88 official regions of the sky. An asterism is any recognisable star pattern that is not an official constellation, often a part of one. The Big Dipper, or Saptarishi, is an asterism within the larger constellation Ursa Major, the Great Bear. Orion's Belt is an asterism within Orion. The Summer Triangle is an asterism made of the brightest stars of three different constellations.
How did Indian astronomers group the stars?
Indian astronomy divided the Moon's path around the sky into 27 nakshatras, star groups that the Moon moves through at a rate of roughly one a day on its monthly circuit. Several nakshatra names point to stars and clusters a child can find today: Rohini is the bright orange star Aldebaran, and Krittika is the Pleiades, the tight little cluster also called the Seven Sisters.
Constellations, galaxies and astrology: what is the difference?
A constellation is a pattern or region of our sky. A galaxy is a real physical system of stars, gas, dust and dark matter held together by gravity; nearly all the stars in every constellation belong to our own galaxy, the Milky Way.
Astrology uses the 12 zodiac signs, named after constellations along the Sun's yearly path, to make claims about personality and the future. Astronomy treats constellations only as a map. One telling detail: the Sun actually passes through 13 constellations during the year, not 12; the thirteenth is Ophiuchus, the serpent bearer, which it crosses from about 29 November to 18 December. See astronomy vs astrology for the full difference.
Constellations are lesson 7 of Astronomy 101, the WhyCosmos live course for ages 8 to 16, covering the 88 official constellations from Ursa Major and Cassiopeia to Crux, and lesson 8 shows how navigators used them.
Questions parents and kids ask
Modern astronomy recognises 88 official constellations, which together cover the whole sky. The list was adopted by the International Astronomical Union in 1922.
No. It is an asterism, a familiar star pattern, within the constellation Ursa Major, the Great Bear. In India its seven stars are known as Saptarishi.
Saptarishi, the seven sages, is the Indian name for the seven bright stars called the Big Dipper or the Plough in English, part of the constellation Ursa Major.
As Earth orbits the Sun, our night side faces different directions in space through the year, so different constellations are above the horizon at night in different months.
Light pollution. Street lights and buildings brighten the night sky, which drowns out fainter stars, so city skies may show only a few dozen of the thousands visible from a dark site.
Very slowly. Every star is moving through space, but the changes are far too small to notice in a human lifetime. Over tens of thousands of years, the familiar patterns will gradually change shape.
Your child asks questions like this every week.WhyCosmos runs live online astronomy classes for ages 8–16, taught by real astrophysicists — where questions like these are the curriculum.
Related terms in this glossary
Sources and further reading