Ursa Major

Ursa Major, the Great Bear, is one of the most famous constellations in the entire sky and one of the easiest to find. Inside it sits an even more famous pattern of seven bright stars called the Big Dipper (in the United States) or the Plough (in Britain). For people living in the Northern Hemisphere, those seven stars are visible all year round and have been used to find direction, tell time, and inspire myths for thousands of years.

  • Best seen fromNorthern hemisphereAlways visible north of approx. 25 degrees N
  • Best viewing timeSpring evenings(Northern hemisphere)
  • Brightest starAliothIn the handle of the Big Dipper
  • Famous asterismBig Dipper (Plough)Seven bright stars, the most recognised in the sky
  • Size rank3rdLargest constellation in the northern sky
  • Famous double starMizar & AlcorEasy to split with the naked eye, in the handle

The Big Dipper, the Plough, the Great Bear

The seven brightest stars in Ursa Major form a famous pattern that goes by lots of names around the world.

  • The Big Dipper (United States) and The Plough (United Kingdom) are the most common modern names.
  • The Great Bear: the four-star bowl is the bear's body, and the three handle stars are its long tail (real bears do not have long tails; ancient Greeks knew that, but the story stuck).
  • The Saucepan (some English speakers) or Charles's Wain (an old British name meaning "Charles's Wagon").
  • In ancient China the same pattern was a giant government carriage.

The Big Dipper is technically an asterism: a smaller recognisable pattern that sits inside a constellation. The full constellation Ursa Major also contains a long line of fainter stars that form the bear's legs and head. The Big Dipper is just the most obvious part.

How to find Ursa Major

From most of the Northern Hemisphere, the Big Dipper is visible every clear night, all year round. It just rotates around the North Star, the way a clock hand rotates around its centre. To find it, face roughly north on a clear evening and look up. You are looking for a clear pattern of seven bright stars in the shape of a saucepan or ladle: four stars making the bowl, three more stars making the handle.

Once you have found the Big Dipper, you can use it to navigate the rest of the sky. The two outer stars of the bowl (Dubhe and Merak) are called the pointer stars. Draw an imaginary line from Merak up through Dubhe and keep going for about 5 times the gap between them. You will arrive at Polaris, the North Star.

Mizar and Alcor: the test of eyesight

The middle star of the Big Dipper's handle is called Mizar. If you look carefully on a clear night, you will see a fainter second star right next to it, called Alcor. The pair has been used for thousands of years as a quick test of good eyesight; some armies historically used it to check whether new recruits had sharp enough vision to be lookouts.

What is really impressive is that Mizar and Alcor are not just an optical illusion: they really do orbit each other, and a telescope shows that Mizar itself is actually four stars orbiting in two close pairs, while Alcor is a binary too. So the "two stars" you see with the naked eye are really a system of six.

Fact The seven stars of the Big Dipper are all moving through space together, almost as if they were a single flock. Astronomers call them the Ursa Major Moving Group, and they think these stars all formed together from the same gas cloud about 500 million years ago. (The exceptions are Dubhe and Alkaid at either end of the pattern; those two are unrelated and just happen to be in the same direction.) In a few hundred thousand years, the Big Dipper will slowly deform as the stars move at different speeds, until the familiar pattern disappears.

The myth of the Great Bear

Most European cultures know Ursa Major as a bear because of an ancient Greek myth. Callisto was a young woman who served the goddess Artemis. The god Zeus fell in love with her, which made his wife Hera so jealous that she turned Callisto into a bear. Zeus eventually placed Callisto in the sky as Ursa Major (the Great Bear), and her son Arcas was placed nearby as Ursa Minor (the Little Bear).

Amazingly, some Native American cultures (like the Iroquois) also saw a bear in the same stars, even though they had no contact with the Greeks. Some anthropologists think this is one of the oldest stories in human culture, dating from before people crossed from Asia to North America 15,000 years ago.

Did you know? The Big Dipper has been used as a symbol of freedom. In the years before the American Civil War, enslaved people in the southern United States used songs about following the "drinking gourd" (the Big Dipper) as coded directions for escaping north. The Big Dipper points to the North Star, and travelling north meant escape from slavery.
Deeper dive: how the Big Dipper will change over time

The night sky looks reassuringly fixed: the same stars in the same patterns night after night, year after year, century after century. But on long enough timescales, even constellations change.

Every star in the sky is moving through space at tens of kilometres per second, but they are so far away that we cannot see the motion over a human lifetime. Over tens of thousands of years, though, the slight differences in direction add up. The five middle stars of the Big Dipper (Mizar, Alioth, Megrez, Phecda and Merak) are all part of the same young star cluster, so they move together. But Dubhe (at the far end of the bowl) and Alkaid (at the end of the handle) are unrelated background stars and are moving in different directions.

Astronomers have used these tiny known motions to figure out what the Big Dipper looked like in the past and what it will look like in the future. About 50,000 years ago the pattern was a much shallower and longer shape, more like a hockey stick. In another 50,000 to 100,000 years, Dubhe and Alkaid will have drifted noticeably out of line with the others, and the saucepan shape will be gone. The Big Dipper as we know it is a temporary alignment.

Once you have found the Big Dipper, you can use it to find Ursa Minor (and the North Star), or jump across the pole to Cassiopeia. For more, see what is a constellation.