Looking Up: Too Hot To Handle?

Aug 5, 2019

Credit public domain

This week on Looking Up Hal zooms in on a star by the name of Nunki. 

There is a fun star in the Colorado sky right now that is pretty neat, the star Nunki, known technically as Sigma Sagitarii. It makes up part of the “teapot’s handle” in Sagittarius and is located below and to the right of the much brighter Saturn.

Nunki is located very near the ecliptic, or the path the planets follow across the sky. It is so close to the ecliptic that in 1981 Venus passed in front of Nunki. It is the brightest star that can be eclipsed by an outer planet, though that hasn’t happened since September 3rd, 423 AD.

We think Nunki is a fairly large star, perhaps five times bigger than our Sun, and at a distance of 225 LY, Nunki radiates far more in the ultraviolet part of the spectrum, making it roughly 3300 times brighter than our Sun. It’s a youngster, and it’s spinning very quickly, perhaps as much as 100 times the rotational speed of our Sun. And like most youngsters who spin around and are very warm, it can’t keep that pace up forever. In as little as 50 M years, a mere tic of the cosmic clock, Nunki will burn out and end up as a white dwarf star, about as big as our Sun. When that happens, the teapot’s handle will appear to be broken.

If you’d like to take a closer look at Nunki, or any of the other wonderful and amazing things in the sky, please visit csastro.org for a link to information on our monthly meetings and our free public star parties.