Speedy Star

You can always count on the stars. Over the course of a human lifetime, their configuration doesn’t change — they don’t appear to move at all.

That static appearance is an illusion, though. The stars are all so far away that we don’t see any motion. Yet they’re all moving in a hurry. And one of the fastest is in view on autumn evenings.

Gamma Piscium is the second-brightest member of Pisces, the fishes. The constellation stretches across the east and southeast at nightfall. Gamma Piscium is near its top right corner — part of a pentagon of faint stars.

Gamma Piscium is a stellar giant. It’s nearing the end of its life, so it’s beginning to get bigger and brighter. Right now, it’s about 10 times the diameter of the Sun, and more than 60 times the Sun’s brightness. That makes it faintly visible to the eye alone, even though it’s more than 135 light-years away.

Perhaps the most interesting fact about Gamma Piscium, though, is its speed. It’s moving across the sky at about 350,000 miles per hour — faster than all but a few other visible stars. At that rate, it’ll move the equivalent of the Moon’s diameter in less than 1500 years.

The star’s composition hints that it came from outside the disk of the Milky Way — the part of the galaxy that includes the Sun. The star has very few heavy elements. That suggests it formed outside the disk, and just happens to be passing through — zipping by like a speeding bullet.

Script by Damond Benningfield