The Big Dipper is one of the most easily recognisable asterisms in the night sky, located in the northern constellation Ursa Major, the Great Bear. It actually goes by many different names, among them the Plough, the Great Wagon, Saptarishi, and the Saucepan, although it will be called the Big Dipper hereafter for ease of understanding. It is particularly prominent in the northern sky in the summer, and is one of the first star patterns a budding astronomer will learn to identify.
The Big Dipper is often confused for the constellation Ursa Major itself and its name is used synonymously with the Great Bear. However, the Big Dipper itself is not a constellation. It just happens to be the most visible part of Ursa Major, which is the third largest of all 88 constellations.
The overall Ursa Major constellation is obviously far bigger than the Big Dipper, but the seven stars that mark the tail and hindquarters of the “Great Bear” are the most visible by far, thus the distinction drawn between them and the larger constellation they are part of. The seven brightest stars in Ursa Major that make up the Big Dipper are called: Alkaid (Eta Ursae Majoris), Mizar (Zeta Ursae Majoris), Alioth (Epsilon Ursae Majoris), Megrez (Delta Ursae Majoris), Phecda (Gamma Ursae Majoris), Dubhe (Alpha Ursae Majoris) and Merak (Beta Ursae Majoris). Alkaid, Mizar and Alioth mark the Big Dipper’s handle, and Megrez, Phecda, Dubhe and Merak outline the bowl. All seven are shown in the diagram below.
You may find it curious as there are obviously only seven stars in the Big Dipper – the name in Chinese, Bei Dou Qi Xing 北斗七星 after all, clearly suggests so. How can the 9 Stars be derived from this? There are many legends and stories that explain this discrepancy. The most popular ones all involve the goddess Dou Mu 斗姆.
Watch out for next posting about Dou Mu 斗姆.