The Big Dipper is one of the most commonly recognized configurations of stars on the northern sky, but it is not by itself a constellation. It is only the most visible part of Ursa Major (Great Bear), the third largest of all 88 constellations. The Big Dipper is an asterism, which is the name given to interesting star patterns that are easily recognizable, but not one of the "official" constellations.
Although only part of the Great Bear constellation, the Big Dipper is an asterism that has been known by different names to different societies, among them the Plough, the Great Wagon, Saptarishi, and the Saucepan.
LOCATING THE BIG DIPPER
Ursa Major lies in the second quadrant of the northern hemisphere (NQ2), which makes it visible at latitudes between +90° and -30°. It is best seen in the evenings in April.
The Big Dipper is circumpolar in most of the northern hemisphere, which means that it does not sink below the horizon at night. As a result of the Earth’s rotation, Ursa Major appears to rotate slowly counterclockwise at night around the north celestial pole.
Depending upon the season of the year, the Big Dipper can be found high in the northern sky or low in the northern sky. Just remember the old saying spring up and fall down. On spring and summer evenings, the Big Dipper shines highest in the sky. On autumn and winter evenings, the Big Dipper lurks closest to the horizon.
The appearance of the Big Dipper changes from season to season. In autumn, it rests on the horizon in the evening. In winter evenings, the handle appears to be dangling from the bowl. In spring, it is upside down in the evening hours, and in summer the bowl leans toward the ground.
ITS MAIN STARS
The Bible refers to the Big Dipper as “the seven stars.” Those stars are named Alioth, Alkaid, Dubhe, Megrez, Merak, Mizar and Phecda.
Alkaid, Mizar and Alioth mark the Big Dipper’s handle, and Megrez, Phecda, Dubhe and Merak outline the bowl.
The brightest star in the Big Dipper asterism is Alioth, Epsilon Ursae Majoris, which is also the brightest star in the constellation Ursa Major and the 31st brightest star in the sky.
Alkaid, or Benetnash, (from the Arabic q?’id bin?t na’sh, or “the leader of the daughters of the bier”) is one of the hottest stars that can be seen with the naked eye.
It is the star marking the tip of the handle of the Big Dipper, or alternatively the tip of the bear’s tail. The name Alkaid means “the leader.”
Mizar (from the Arabic m?zar, or “girdle”) consists of two double stars. It was the first double star to be photographed, in 1857. It is the middle star in the Big Dipper’s handle. Mizar has an apparent magnitude of 2.23 and is 82.8 light years distant.
Alioth (from the Arabic alyat, “fat tail of a sheep”) is the star in Ursa Major’s tail which is the closest to the bear’s body.
Megrez (from the Arabic al-maghriz, “the base,” referring to the base of the Big Bear’s tail), is the dimmest of the seven stars.
Phecda, or Phad (from the Arabic fakhð ad-dubb, “the thigh of the bear”), has the stellar classification A0Ve, which makes it another white main sequence dwarf.
Dubhe (from the Arabic dubb, meaning “bear,” abbreviated from the phrase ?ahr ad-dubb al-akbar, which means “the back of the Greater Bear”) is an orange giant and the second brightest star in the constellation.
Merak (from the Arabic al-maraqq, “the loins”) is a white main sequence star of the spectral type A1V. It has an apparent magnitude of 2.37 and is 79.7 light years distant from Earth.