This lesson was created as a part of the SMART website and is hosted by the Illinois Institute of Technology
What's up? The Sky! What could be more geometrical than the sky? The Summer Triangle is overhead shortly after sunset in the late summer and well thru the Fall. This phenomenon is made up of three stars, each part of its own individual constellation. Go outside 45 minutes after sunset and just look up. Chicago skies are so light-polluted that only the brightest stars are visible. Vega, Deneb and Altair are such stars. Vega belongs to Lyra, the Lyre. Deneb is part of the Northern Cross, a.k.a. The Swan. (The tail of the swan is the top of the cross.) Altair is part of Aquila, the Eagle. The rest of the stars in each constellation are not all that visible.
The brightest star Vega has two close stars to its lower right. The other stars of the Cross/Swan are visible with Deneb. Altair is pretty much unadorned and this distinguishes it from the other two. They appear in that order, Vega, Deneb and Altair, on a clear night. This picture shows the way the triangle presents itself. First to appear is Vega, then Deneb and finally Altair. All this action is in the East. High in the Southwest is Arcturus and to the South is Antares. These are about all there is to see, except for the moon, with the naked eye this close to sunset. It is just too soon to spot any planets.
Get to know this star group because it is a guide to the rest of the Summer/Fall night sky