The brightest star of Pegasus, the flying horse, is a bit difficult to pin down. Depending on how you define the constellation, two stars can claim the title. And one of those two changes brightness, so other stars in Pegasus can outshine it. The brightest star in the classical connect-the-dots picture of Pegasus is known as Alpheratz. It’s in the Great Square, a pattern of four stars that outlines the horse’s body. In the 1930s, though, astronomers drew precise boundaries for all the constellations. In this system, Alpheratz is just across the border of Andromeda, where it’s that constellation’s leading light. That leaves Pegasus with a fainter luminary: Enif, from an Arabic name that means “the horse’s nose.” Enif is a supergiant. It’s perhaps a couple of hundred times wider than the Sun, and thousands of times brighter. Enif doesn’t shine steadily, though. Instead, its brightness varies by a few percent. The change doesn’t follow any discernible pattern, so no one knows exactly how
