The Big Dipper
The Big Dipper is one of the most recognizable and easily found patterns of stars in the night sky. It includes seven bright stars from the constellation Ursa Major with four stars forming the bowl and three stars forming the handle.
Ursa Major, also known as the Great Bear, is a large constellation that includes more stars than those in the Big Dipper.
However, the stars that make up the bear’s head, torso, legs and feet are not as easy to see as the seven stars that make up the hindquarters/flank and tail which form the Big Dipper.
The Big Dipper is not a formal constellation but an asterism, a shape or pattern of stars that are often part of a constellation.
Stars in the Big Dipper
There are seven stars that make up the asterism, they include:
Dubhe (Alpha Ursae Majoris) is the second brightest star in the asterism and forms the upper outer portion of the bowl. It is an orange giant star with a visual magnitude of 1.79 and is approximately 83 light-years in distance.
Merak (Beta Ursae Majoris) forms the bottom outer portion of the bowl, with a mass three times that of the Sun. It is a white subgiant star with an apparent magnitude of 2.37 and is 79 light-years distant.
Phecda (Gamma Ursae Majoris) forms the bottom inner portion of the bowl. It is a main sequence dwarf star with an apparent magnitude of 2.4 and lies 83.2 light-years distant.
Megrez (Delta Ursae Majoris) is the dimmest star in the asterism, and forms the upper inner portion of the bowl, connecting to the first star in the handle. It is a main-sequence star and lies 80.5 light-years in distance.
Alioth (Epsilon Ursae Majoris) is the brightest of the seven stars in the asterism and is the start of the handle. It has a visual magnitude of 1.77 and is 82.6 light-years away.
Mizar (Zeta Ursae Majoris) is a multiple star system with two binary stars and is located in the middle of the handle. It has an apparent magnitude of 2.23 and is 83 light-years away.
Alkaid (Eta Ursae Majoris) is a young blue main-sequence star and is the third brightest in the Ursa Major constellation. It forms the end of the handle with an apparent magnitude of 1.86 and is roughly 104 light-years distant.
How to Find the Big Dipper
Ursa Major, and therefore the Big Dipper, is visible at latitudes between +90 and -30 degrees on most clear nights in the northern hemisphere.
Both the Big Dipper and Little Dipper are circumpolar, meaning they rotate counterclockwise around the North Star as the Earth spins and never dip below the horizon at night.
There is an old saying ‘spring up and fall down’ that refers to the Big Dipper’s position in the sky during the seasons. In spring and summer, the asterism will be at its highest in the sky, while during the fall and winter it will be closer to the horizon.
Look for a dot-to-dot pattern in the shape of a kitchen ladle. If you locate the Big Dipper then you can easily locate the Little Dipper and North Star.
Big Dipper, the Guide
Since the Big Dipper is easy to find in the sky, it makes a good starting point for beginners to learn about the stars in the northern hemisphere. For this reason, it is also used as a guide to locate other stars in the sky and surrounding deep-sky objects.
For example, the best way to locate the Little Dipper (i.e. Ursa Minor) and the North Star (i.e. Polaris) is to use the Big Dipper.
The two outer stars of the bowl, Merak and Dubhe, point towards the end of the handle in the Little Dipper. An imaginary line between the two stars from the Big Dipper will extend towards Polaris.
Use the Big Dipper to find Polaris the ‘North Star’
If your sky is dark enough, once you have found Polaris you will also be able to find the rest of the Little Dipper. Its stars are rather dim so it is not as easy to observe from a light-polluted sky.
Use the Big Dipper to find other deep-sky objects
Origins and Associations
There are many parallels associated with Ursa Major and the Big Dipper among different cultures.
Some Native American’s believe the bowl is actually the bear and the stars in the handle are warriors chasing the bear.
In the United Kingdom and Ireland, the Big Dipper is known as the Plough and is thought to have been associated with an old Nordic constellation that was believed to represent a wagon or chariot.
It is seen as a ladle (China/Japan), a cleaver (northern England), a cart/wagon (Germany/Hungry) and a coffin (Saudi Arabia).
It was also associated with the Underground Railroad during the Civil War. Slaves referenced the asterism in a song called ‘Follow the drinking gourd’ which provided directions to follow the Big Dipper to the north and to freedom.