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The Summer Triangle



As dusk deepens into night in early June, look a bit north of east, not real high in the sky, for a sparkling blue-white star, whose name is Vega. Reigning at the apex of the celebrated Summer Triangle, Vega overwhelms as the brightest of the triangle's three glorious stars, all bright enough to be seen from almost any light-polluted city.

At nightfall, look for another blue-white Summer Triangle star to the lower left of Vega: Deneb, the brightest in the constellation Cygnus, the swan. It shines close to the northeastern horizon, and an outstretched hand at an arm length away gives you some idea of its distance from Vega.

About an hour after dark in early June, the Summer Triangle's bottom star, Altair, twinkles to the lower right of Vega, almost due east. A ruler held at an arm's length spans the gap between these two stars.

Since the stars rise some four minutes earlier with each passing day, expect the stars of the Summer Triangle to light up the twilight dusk around middle to late June -- a sure harbinger of the change of seasons, of spring giving way to summer. All night long, the stars of the Summer Triangle, as if a trio of school kids on vacation, waltz amidst the streetlights of the Milky Way Galaxy.

Yes, if you're lucky enough to be under a dark starry sky on a moonless night, you'll see the great swath of stars known as the Milky Way passing between Vega and Altair, with Deneb bobbing in the middle of this river of stars that meanders across the heavens. Although every star that you see with the unaided eye actually belongs to the Milky Way Galaxy, oftentimes the term "Milky Way" refers to the cross-sectional view of the galactic disk, where innumerable far-off suns congregate into a cloudy trail of stars.

Once you find the Summer Triangle, try your luck at locating Cygnus, the swan. Deneb represents its tail, and the "eye" of the swan - the star Albireo - is found roughly halfway between Vega and Altair. The great bird is flying south, pretty much parallel to the eastern horizon at early evening.

Some people have an easier time seeing Cygnus' stars as the Northern Cross, Deneb being the top of the Cross and Albireo, the bottom. The Cross, however, appears sideways at early evening. Click here to see a photo of the stars that make up Cygnus or the Northern Cross, and click here to have its stars connected for you.

Once you master Cygnus or the Northern Cross, you can always find the backbone of the Milky Way Galaxy. Extending the Deneb-Albireo line in either direction sends you soaring along the galactic equator -- a starlit boulevard abounding with celestial delights. Use binoculars to reel in the gossamer beauty of it all, the haunting nebulas and star clusters of a midsummer night's dream!


copyright 2003 by Bruce McClure


Another June Feature: Escape Velocity