Sky Triangles

Sky Triangles

Manning, Jim
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In the West, triangles have a certain “Come and get it!” quality, as any hungry cowpoke at the end of a long day can tell you: the clang of the metal triangle—the dinner bell from the chuckwagon--was music to his stomach.

The sky can have a sort of come-and-get-it ambience as well on a clear, autumn night bristling with stars, and traingles are easy enough to find: pick any three stars and you’ve got one. The Summer Triangle for example, made of the bright stars Deneb, Altair, and Vega, which now westers earlier and earlier in the evening, carrying summer away with it.

You can find smaller triangles in the fall sky by first finding another shape—the Great Square of Pegasus. This flying horse rides high across the south on chill autumn evenings, due south by 11 pm in early October. The square forms the front portion of the upside-down equine pictured as rising from the sea. The upper left-hand star of the square (Alpheratz) doubles as the head of Andromeda, who flails up and left in a shape resembling a steer’s horn.

Now, look above her body stars and you can find a faint, oblong glow that marks the Andromeda Galaxy, a “nearby” edge not quite three million light years away (try binoculars to see it better). Below her body you’ll spot a small, narrow isoceles triangle of faint stars which is, well, “the triangle,” or Triangulum. Sometimes imagination even failed the Greeks.

They nonetheless offered some alternate notions, such as the triangle representing the Nile delta, or the island of Sicily; it’s also said that the Greeks called it Deltoton, for its resemblance to the capital letter delta in the Greek alphabet. But sometimes, a triangle is just a triangle.

Don’t fret; if you scoot a little farther down and to the right of Triangulum, you can find the slightly brighter and oblong triangle that forms the best part of Aries the ram. There’s not a lot more to see than at Triangulum--think of the triangle as forming the head and curling horn of the ram, with the rest of the body lying vaguely among the fainter stars down and left--but at least Aries was a constellation of the zodiac and something the Greeks could sink their teeth into.

Aries was the ram with the famous golden fleece sought by Jason. The ram ended up in the kingdom of Colchis after two children, Phrixos and Helle, used the golden sheep to escape an untimely end plotted by their evil stepmother. Alas, Helle, the girl, lost her grip on the way across the narrow strait separating Europe from Asia and fell in; the Greeks called it the Hellespont (today, the Dardanelles). But the boy, Phrixos, hung on. He sacrificed the ram in thanksgiving afterward. Zeus got the carcass, which he placed in the starry sky, and Phrixos got the golden pelt, which he traded to the local king, Aeetes, for his daughter’s hand in marriage. King Aeetes tacked the fleece to an oak tree in a sacred wood guarded by a monster, and there it remained--until Jason came looking for it.

Jason was the rightful heir to the kingdom of Thessaly, but his usurping cousin Pelias was on the throne, and said he wouldn’t give it up until Jason brought him the fleece. So Jason loaded up the good ship Argo and set off. They reached Colchis, and another of King Aeetes’ daughters, Medea, became smitten and helped Jason bewitch the monster, snatch the fleece, and escape to Greece. Jason got his throne, the girl, and the fleece, which he hung in the temple of Zeus. And the ram itself still hangs in the sky.

Not surprisingly, there’s another official triangle in the southern sky, named Triangulum Australe; it’s bigger, brighter, and lies near Alpha and Beta Centauri, not far from Jason’s ship Argo, made up of the constellations Carina (the keel), Puppis (the stern), and Vela (the sails).

But then, one can make many triangles in the sky. When autumn nights are clear, and those sky triangles twinkle their come-and-get-it calls, answer them and look up. You never know what adventures may await!




Jim Manning is head of the Office of Public Outreach at the Space Telescope Science Institute in Baltimore, Maryland, but maintains Montana roots just "Outside Bozeman."

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