Nestled between the constellations of Andromeda, Perseus and Pisces is a curious little trio of stellar triangles, visible on crisp November evenings. Each triangle has an interesting history all its own.

The upper triangle is the only constellation in the sky that looks exactly like what it is supposed to be. No imagination is required to pick out the constellation of Triangulum, the Triangle. Ancient Greek astronomers invented Triangulum, perhaps to honor the brilliant work of the great Greek mathematician Pythagoras. Every high school student who has suffered through a geometry class has studied the Pythagorean theorem: in any right triangle, the sum of the squares of the lengths of the legs equals the square of the length of the hypotenuse. One need look no further than the stars of Triangulum to be reminded of this important theorem.

Of the 88 constellations, only 10 are smaller than Triangulum. Like its much larger neighbor, Andromeda, Triangulum boasts a large spiral galaxy within its borders, M33, or, the Pinwheel Galaxy. I’ve glimpsed M33 with the naked eye on exceptionally clear, dark nights, but using binoculars makes it easier to see. It is smaller and more distant than Andromeda’s famed galaxy, M31, but at 3 million light years away, M33 is still a member of our local group of galaxies.

Below the southern tip of Triangulum is another distinctive triangle of stars. This one marks the head and horns of Aries the Ram, the first constellation of the zodiac. The brightest star in this triangle is named Hamal, meaning “the head of the sheep.” The constellation of Aries also dates back to the early Greeks, who imagined these stars to be the ram that wore the Golden Fleece, the treasure sought by Jason and the Argonauts in their epic journey.

Below the northern end of Triangulum is a third triangle of stars. While this tiny asterism officially lies within the boundaries of Aries, the Ram, it has been identified through the ages with a number of now defunct constellations. It first appeared as an asterism separate from Aries in 1612 on a star chart published by Petrus Plancius as Apes, the Bee. In 1624, it appeared on a star chart published by Jacob Bartsch as Vespa, the Wasp. Then, in 1674, Frenchman Ignace-Gaston Pardies resurrected the little triangle as Lilium, the Lilly.

It appeared one more time as Musca, the Fly, on the famous star atlas published in 1690 by Johannes Hevelius. After that, this little trio of stars was reabsorbed into the constellation of Aries, and it appears as though that will be its permanent home.

Step outside about 7 p.m. in mid-November and look about halfway up in the eastern sky. There, you will find autumn’s little trio of triangles: Triangulum, Aries and the star pattern formerly known as The Fly.

Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Steamboat Springs Campus. His “Celestial News” column appears weekly in Steamboat Today. Check out Westlake’s new “2017 Cosmic Calendar” of sky events on his website, jwestlake.com. It features 12 of his best astro-photos and a day-by-day listing of cool celestial events you and your family can enjoy watching all year.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Steamboat Springs Campus. His “Celestial News” column appears weekly in Steamboat Today. Check out Westlake’s new “2017 Cosmic Calendar” of sky events on his website, jwestlake.com. It features 12 of his best astro-photos and a day-by-day listing of cool celestial events you and your family can enjoy watching all year.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Steamboat Springs Campus. His “Celestial News” column appears weekly in Steamboat Today. Check out Westlake’s new “2017 Cosmic Calendar” of sky events on his website, jwestlake.com. It features 12 of his best astro-photos and a day-by-day listing of cool celestial events you and your family can enjoy watching all year.