Summer Triangle Rides High

As is typical of the evening sky for two weeks each month, the Moon washes out the dimmest stars tonight. Three stars it won’t wash out, however, are Deneb, Altair and Vega – members of the Summer Triangle. These three bright stars are among the brightest in the northern hemisphere and are riding very high in the western sky tonight about 30 degrees apart. The name Summer Triangle is something of a misnomer; it is easily visible well into November.

As stars go, Altair and Vega are close neighbors of the Sun, being only 16 and 25 light years away respectively. Deneb is quite distant at 1,550 light years–to shine so brightly from so far away it must be some 70,000 times more luminous than our Sun!

A week or so from now, when the Moon is not visible you will be able to trace out the constellations the three stars of the Summer Triangle belong to: Aquila the eagle, Cygnus the swan, and Lyra the lyre. The two bird constellations really do look like stick-figure birds, and Lyra has a very distinctive parallelogram shape in it. Both Cygnus and Aquila are embedded in the Milky Way and have numerous star clusters and nebula scattered throughout. They will look like little smudges in your binoculars. One sight you do not want to miss with your binoculars is Albireo, the star in the beak of the Swan. Steady hands will reveal to the sharp-eyed that this star is not one, but two stars colored yellow and blue.

Next week, draw an imaginary line from Deneb down through Vega and you will pass through the constellation of Hercules; the line will pass just to the left of the rather faint rectangle-like shape of the asterism known as the Keystone. Scan with your binoculars along the lower edge of the Keystone and you will see the faint smudge of M13–a globular cluster consisting of several hundred thousand stars 25,000 light years away.

You will note that the constellation, Hercules, as drawn does not look much like a man; constellations only occasionally look like the objects they are supposed to represent. The lines are drawn only to serve as a mnemonic to help one find their way around in the sky. Lines date from the early 19th century when they replaced the elegantly drawn images dating from antiquity. There is, in fact, no official way to draw the lines; artists are free to make up their own variations. Nowadays constellations are defined as a particular patch of sky, not by the stars making them up.

Michael Usher is Vice President of the Everglades Astronomical Society. They meet every second Tuesday at 7:00PM at the Norris Center, Cambier Park, Naples.