Pegasus

Pegasus has a bit of an identity crisis. The stars that outline its body – the Great Square – don’t all belong to the flying horse. In fact, the brightest of the four stars officially belongs to Andromeda. The Great Square is in the east at nightfall. Its member stars are all bright enough to see even through moderate light pollution. The square is tilted, so it looks more like a diamond than a square. Its brightest member forms the left point of the diamond – the star Alpheratz. It’s about a hundred light-years from Earth. And it consists of two stars, both of which are a good bit bigger, brighter, and heavier than the Sun. In earlier centuries, Alpheratz was considered a member of both Pegasus and Andromeda – it’s a prominent member of the classical outlines of both constellations. But in the early 20th century, astronomers decided to formalize the constellations. In 1930, they adopted a list of 88 constellations and gave them precise boundaries, like the borders of states or nations. That meant that every star could belong to only one constellation. The way the borders were drawn, Alpheratz stayed with Andromeda. There’s no way to not see the star as part of the Great Square. So unofficially, Alpheratz maintains its dual citizenship: the second-brightest star of Andromeda, and the brightest star of the Great Square of Pegasus. We’ll have more about the flying horse tomorrow. Script by Damond Benningfield