Fomalhaut, the “autumn star,” rolls low across the south this evening. It’s easy to pick out because it’s the only bright star in that entire region of the sky.
Fomalhaut represents the mouth of Piscis Austrinus, the southern fish — a constellation that dates from antiquity. But today, it’s a bit different from when it was first drawn — it’s lost its tail. Four centuries ago, the stars that formed the tail were split off to make a new constellation: Grus, the crane. From the southern half of the United States, it strides low along the southern horizon, below Fomalhaut.
The crane’s brightest star is Al Nair. The name is a shortened version of an Arabic name that means “the bright one in the fish’s tail.” The star is pretty bright, but it’s also pretty low in the sky, so it’s tough to see if you’re north of about Albuquerque or Atlanta.
Al Nair is a bit more than 100 light-years away. In other words, we see the star as it looked a bit more than a century ago. If we could see it in real time, though, it’s unlikely that we’d notice any difference — the star probably probably hasn’t changed much over the past century.
Even though we can’t see it, Al Nair is changing — it’s nearing the end of its normal lifetime. That alters the nuclear reactions that take place deep in its core. Those changes will cause the star to get bigger and brighter. But that probably won’t be noticeable from here on Earth for millions of years.
Script by Damond Benningfield