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After-Summer Triangle

The Summer Triangle defies its name, for the asterism is well-placed for autumn viewing. The triangle defined by the bright stars Vega, Deneb, and Altair will guide you to both prominent and obscure constellations. It's like a stage containing both lead actors and lesser-known bit characters, already risen in the east after sunset and moving high overhead through the night.

The Summer Triangle, in red, is nearly a 30-60-90 triangle. The uppermost and brightest star in the autumn evening--the 90 degree corner--is Vega, which anchors the small constellation Lyra the Harp. Lyra has a distinctive parallelogram within the Summer Triangle, and if you have a telescope you may see a fuzzy circular feature, circled, between the end two stars. M57 is the Ring Nebula, an expanding cloud of gas expelled from a dying star.

The northernmost corner of the triangle, bottom left on early autumn nights, is the star Deneb. From Deneb, look inside the triangle to find the large asterism Northern Cross. The three upper cross stars are bright, but you'll readily find the entire outline. The base of the cross is the faint star Albireo, circled, but a modest telescope reveals it actually to be a double star. It's a beautiful pair, with one star being blue and the other reddish.

Deneb marks the tail of Cygnus the Swan, with the Northern Cross being a stick figure version of the swan. (Reminder: a baby swan is a cygnet.) The full swan indeed looks like its namesake when you include the fainter stars connected in the image. With its outstretched wings, the swan is flying south through a hazy swath of diffuse light--the Milky Way! Billions of individual stars that make up our galaxy collectively appear as a faint ribbon across the sky, and Cygnus helps you find it easiest. Of course, it's best viewed from a dark sky.

In addition to prominent constellations, it's fun to find some fainter patterns in the sky that have been recognized by cultures over the years. The third star of the Summer Triangle is Altair, which is the head of Aquilla the Eagle (not outlined here). Just inside the triangle from Altair is faint Sagitta the Arrow. (Reminder: Sagittarius is the Archer.) Once you find it you know it, and it's a simple pleasure to pick out four inconspicuous stars that go unnoticed by most people.

East of Sagitta, outside the boundary of the Summer Triangle, is a delightful light group known as Delphinus the Dolphin. Again, once you see it you'll come back to Delphinus repeatedly. It's like your being the theater-goer who is a parent of the bit actor--you see past the famous ones and delight in the supporting cast.

Here's the starfield without the lines, facing east in mid-August. Find Vega, then anchor yourself with the 30-60-90 triangle. From Deneb find the Northern Cross. Then seek the nearby treasures of the night sky. It's a great way to extend your summer joy beyond the confines of just the warmest months.


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