Equuleus

Pegasus, the flying horse, is beginning its climb into the evening sky. It clears the eastern horizon by midnight. It’s preceded into the sky by another horse, to its upper right.

Equuleus is far smaller and less prominent than its famous equine cousin. In fact, of all the constellations passed down from the ancient world, it’s by far the smallest.

Unlike most ancient constellations, there’s not much of a story associated with Equuleus. And as it’s drawn in the sky, it’s not even a full horse -- only a head, which is outlined by a lopsided rectangle of four meager stars.

The brightest is Alpha Equulei. It’s actually a pair of stars locked in a tight orbit around each other. Both stars are about twice as massive as the Sun, with one slightly heavier than the other.

That difference in heft has made a big difference in the lives of the two stars. The heavier one has already ended its “normal” lifetime, and is entering one of its final stages -- it’s puffed up like a giant orange balloon.

The smaller star is still in the prime of life. But as the bigger star expands, the surfaces of the two stars may get so close that the stars will begin to swap some of their gas -- a process that may alter the evolution of both stars.

Equuleus is in the east at nightfall. It’s below Delphinus, the dolphin -- another small constellation, but one that’s much easier to pick out.
 

Script by Damond Benningfield