What Is The Big Dipper?
QUICK ANSWER
The Big Dipper is a famous pattern of seven bright stars in the night sky, but it's technically not a constellation. It's an asterism, a recognizable star pattern that's part of the larger constellation Ursa Major (the Great Bear). The Big Dipper points the way to Polaris, the North Star.
The Big Dipper is one of the most recognizable star patterns in the northern sky. Most people think of it as a constellation, but it's actually an asterism, a smaller pattern within a larger constellation called Ursa Major. The Big Dipper has been used for navigation, storytelling, and timekeeping for thousands of years. From mid-northern latitudes, it's visible year-round.
Is it a constellation?
No, technically an asterism. According to NASA, asterisms are familiar star patterns that aren't officially constellations. The Big Dipper is the most famous asterism in the Northern Hemisphere, but it's part of the constellation Ursa Major (the Great Bear), which is the third-largest of the 88 official constellations. Other names for the Big Dipper include the Plough (in the UK), the Wagon, and the Great Cart. Different cultures have named it differently throughout history.
What stars make it up?
Seven main stars: four forming the bowl and three forming the handle. From the end of the bowl, the stars are Dubhe, Merak, Phecda, Megrez, Alioth, Mizar, and Alkaid. Mizar is famous as a multiple star system; it has a faint companion called Alcor visible to the naked eye in dark skies, used historically as an eye test. Most of the Big Dipper's stars are tens to hundreds of light years from Earth. The pattern we see is an accident of our viewing angle; the stars aren't actually close to each other in space.
How do you find Polaris with it?
Use the pointer stars at the end of the bowl. The two stars at the end of the Big Dipper's bowl (Dubhe and Merak) are called the pointer stars. Draw an imaginary line from Merak through Dubhe and extend it about five times that distance. You'll arrive at Polaris, the North Star, which sits at the end of the Little Dipper's handle. This trick has been used by navigators for thousands of years to find true north. Polaris isn't a particularly bright star but stays nearly fixed in position.
When can you see it?
Year-round from much of the Northern Hemisphere. For observers at high northern latitudes (like the northern United States and Canada), the Big Dipper is circumpolar, meaning it never sets and is visible on any clear night. Its orientation changes throughout the year: in spring and summer, it appears high in the sky; in fall and winter, it's lower toward the horizon. The old saying spring up and fall down refers to this seasonal shift. From the Southern Hemisphere, the Big Dipper is harder to see or not visible at all.
The Big Dipper is a famous asterism made of seven bright stars in the constellation Ursa Major. It's not technically a constellation itself. The pattern includes the pointer stars Dubhe and Merak, which point the way to Polaris (the North Star). The Big Dipper is circumpolar from much of the Northern Hemisphere, meaning it's visible year-round on any clear night. Its position in the sky changes with the seasons.
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