I hope you have been enjoying the dog days of summer. One reason these might be called the dog days is because Sirius, the dog star, is now roughly aligned with the sun. Since Sirius is the brightest star visible from Earth, an old story said that its brightness contributed to the sun’s heat at this time of year.
With Sirius out of the picture right now, that leaves yellow Arcturus and blue Vega vying for top honors as the brightest stars in our sky this month. Both are listed as magnitude 0.0. You can see Arcturus shining brightly in the western sky, and Vega will be near your zenith (i.e. the point straight over your head).
Vega is in the constellation Lyra (the Lyre), a rather small constellation but one that has a couple of my favorite telescope targets. The visible stars in Lyra form a small equilateral triangle and an adjacent parallelogram. Vega is part of the triangle; all the other stars are much dimmer.
The dimmer star in the triangle that is away from the parallelogram is called Epsilon Lyrae, and is actually a multiple star system. With a small, low-power telescope, it is easy to see two equally bright stars. But with higher magnification, and at least a 3-inch diameter telescope, you can see that both stars in the double are also double stars. This double-double is a great test of the resolving power of a telescope.
At the other end of the parallelogram from the triangle is the Ring Nebula, or M57, one of the more famous planetary nebulae. It is right on the line between the two stars so easy to point your telescope to, but with low magnification, you might mistake it for just another star. Upon close inspection, you can tell it is a bit too fuzzy to be a star, and at higher magnification, you can make out the doughnut-shaped nebula.
A planetary nebula is an expanding cloud of gas from a mid-sized star nearing the end of its life. Rather than a big explosion, the sun is also expected to go through such a planetary nebula stage when it runs out of fuel in its core.
The word planetary in the term planetary nebula is just descriptive – it means it looks small and disk-like in a telescope. The nebula part of the name just means they are fuzzy. So looking through a telescope, a planetary nebula is a small, disk-like, fuzzy thing that has nothing to do with planets.
Along with Vega, the bright stars Deneb and Altair make the summer triangle. From Vega, Deneb is about two and a half fist widths to the northeast and Altair is about three and a half fist widths to the south. The appearance of the asterism of the summer triangle in the early evening sky signals the beginning of summer, and it will be with us for the next few months.
Vega, Deneb and Altair, and their respective constellations Lyra, Cygnus and Aquila are a good anchor for learning the rest of the summer sky.
You have a few more weeks to catch Mars and Saturn close to each other in the western sky before they set. This weekend they are a little more that 3 degrees apart.
[email protected] Charles Hakes is an assistant professor in the physics and engineering department at Fort Lewis College and is director of the Fort Lewis Observatory.