Jupiter is high overhead now. Except for the moon, it will be the brightest thing in the evening sky this month, and is a good pointer to part of a rather large asterism.
An asterism is just a recognizable pattern of stars, and the one I am writing about this month is called the winter hexagon. Although a hexagon has only six sides, this asterism will help you learn eight different bright winter stars in six different constellations. The way you get eight stars is that the center of this hexagon has a bright star, and one of the points has a pair of twin stars. Learning these brighter stars in the region will help you star-hop to the numerous faint clusters and nebulae requiring binoculars or a telescope.
Let’s start in the center. If you can find Orion, Betelgeuse is the bright red star above and to the left of the three belt stars. This is the center of the hexagon, and a good starting place to tell you how to find the six points around the edge.
We’ll start with the brightest point, Sirius, and continue counterclockwise. Sirius is the brightest star in the sky, but if you need help finding it, the belt stars of Orion point southeast to Sirius. Sirius is in the constellation Canis Major, the Big Dog, one of Orion’s two hunting dogs.
The second point of the hexagon is at the other end of Orion from Betelgeuse. Rigel, Orion’s foot, is approximately equal distance from the belt stars as Betelgeuse, but is much bluer, so is a much hotter star. With the center and two points identified, you now have an idea of the size of the winter hexagon.
The third point around the edge is the red star Aldebaran in the constellation Taurus. It doesn’t look so bright now, because it is right next to the much brighter Jupiter. Without Jupiter as a pointer, you can find Aldebaran on a line between the belt stars in Orion and the Pleiades (Seven Sisters) open cluster in Taurus.
Continuing counterclockwise, the fourth point is Capella, in the constellation Auriga. It is slightly east of straight north from Aldebaran, and will be the point opposite of Sirius in the hexagon.
The fifth point is the one with two stars. Castor and Pollux are the twins of Gemini. They are roughly equal in magnitude. Castor is a beautiful double star in a small telescope, but I will have to save a discussion of double stars for another article.
Many nonstargazers know the names Castor and Pollux, either from mythology or from reading their horoscope, but a common problem that many stargazers have is remembering which is which in the sky. I just remember that Castor, with the “C,” is on the same side as Capella, and Pollux, with the “P,” is on the same side as Procyon.
Procyon is the sixth point, and the eighth star in the hexagon. It is in the constellation Canis Minor, the Little Dog. Not only is it a lesser dog, it really is a lesser constellatio because there are only two stars in it above third magnitude.
So this month, see if you can find all eight stars. And then next month, see if you can do it from memory.
Charles Hakes is an assistant professor in the physics and engineering department at Fort Lewis College and is director of the Fort Lewis Observatory.