A NOTE ABOUT LATITUDE: These sky charts assume an observer at 40 degrees north latitude; much of the world's population lives within 20 degrees or so of 40 degrees north, so it is a useful latitude assumption. However, if you are north of this latitude, the stars will all appear shifted towards the south; if you reside south of this latitude, the stars will appear shifted to the north.
Autumn skies in the northern hemisphere demonstrate some significant change. There are just a few first magnitude stars visible, so much of what can be seen relies on second magnitude stars. Towards the west, the Summer Triangle largely contains the few first magnitude stars that can be seen at this time of year, so looking there to find our way around is a good way to start. First, watch this video (COMING SOON) on how to measure distance in the sky. And if you are unsure about the differences in magnitude, check out this video (COMING SOON) first as well.
The brightest star is Vega, heading up the diminutive constellation Lyra the Harp. To the south, and slightly dimmer is the first magnitude star Altair in Aquila the Eagle. And rounding out the triangle to the east of Vega is Deneb, forming the tail of Cygnus the Swan. The neck of Cygnus extends into this large triangle, while Aquila aims in a similar direction towards the south. A line from Deneb through Cygnus will place you at the “Keystone” asterism of Hercules, wherein the globular cluster M13 resides. But Hercules is made up of dim stars, so this may be a challenging area to see, as it gets lower in the west.
A line from Vega through Altair, and extending another 20 to 25 degrees, places the observer at the star Dabih in Capricornus. A dim constellation, but looking east of there towards the southern horizon will help you spot the only first magnitude star in this part of the sky: Fomalhaut, of Pisces Austrinus – the Southern Fish. Between these stars is the ecliptic, and there really aren't any bright stars during autumn that are near the ecliptic. So if you see a bright spot in the south that is not Fomalhaut, you just may be seeing a planet, and not a star.
Back at the Summer Triangle, look from Vega, through the southeastern wingtip of Cygnus, which is Epsilon Cygni. Extend another 35 degrees past this star, and this will place you at the “neck” of Pegasus the flying horse, at Alpha Pegasi. Pegasus' nose extends towards the west from here; while 3 more 2nd magnitude stars form a near perfect square in the sky on the other side. Each side of this square is very nearly 15 degrees in length. However, the star opposite from Alpha Pegasi is actually not technically part of this constellation, despite being termed “The Great Square of Pegasus.” This star is actually Alpha Andromedae, of the constellation Andromeda the princess. Moving another 15 degrees the opposite direction from Pegasus' head, we find Beta Andromedae, and another 15 degrees out, Gamma Andromedae.
Now go one more “step” of 15 degrees. This places you at Mirfak, or Alpha Persei, the brightest star in Perseus the hero. The Milky Way runs through this area of sky, and there are some wonderful open star clusters to see with both binoculars and telescopes. Now, one last 15 degree hop places us towards the horizon, and the first magnitude Capella will be rising off the northeastern horizon. But that's a little low in the sky. If we look slightly above Mirfak in Perseus, we can see a sideways “W” or “M” shape. This is Cassiopeia, the queen, and her king-husband Cepheus is just a short hop away, by following a line from Alpha Cassiopeiae through Beta Cassiopeiae. The “king” looks sort of like an upside down house shape at this time of year, and despite having the Milky Way running right through it, most of the stars in Cepheus are dim.
To the east, there are winter constellations and stars rising that may be visible, such as Orion, Taurus and Capella among others. Click ahead to see the Winter Constellations page, as these constellations will be visible later at night during the autumn months.
But that should help you find your way around the autum sky – give it a try on a clear night, and if you want to see more, look for the star charts at this site for deep sky objects you may be able to spot in the autumn sky as well.