Thursday, October 23, 2008

Lady in Chains

The constellation of Andromeda the Chained Woman is one of the premiere sights of the autumn sky. In Greek mythology, Andromeda (ann-DROMM-eh-duh) was the daughter of King Cepheus (SEE-fee-yuss) and Queen Cassiopeia (kass-ee-oh-PEE-yuh). Because the insufferably vain Cassiopeia offended the gods, Andromeda was chained to a rock by the sea as an offering to the sea monster Cetus (SEE-tuss).

The Royal Family: Cepheus, Cassiopeia, Andromeda & Perseus
Star maps created with
Your Sky

Cassiopeia the Queen, Cepheus the King, Andromeda, and Andromeda’s rescuer and subsequent husband, Perseus the Hero, are all immortalized in the night sky as constellations. The four star groups are known collectively as the Royal Family. They can be observed together in the night sky after sunset, in fall and winter. Also lurking nearby, through early winter, is the constellation Cetus the Sea Monster, aka Cetus the Whale.

Let’s take a closer look at the stars of our damsel in distress.

1) Wait at least one hour after sunset to begin observing, so that twilight’s faded and your sky’s good and dark.

2) Since we’re approaching New Moon on October 28th, you’ll have plenty of dark hours to observe before the Moon rises.

3) Face east. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your back to the west, and you’ll be facing approximately east.

4) First find the Great Square of Pegasus, about halfway between the zenith (the point in the sky directly above your head) and the eastern horizon. The Great Square is an asterism, a recognizable star pattern, within the constellation Pegasus. It's defined by four bright stars, one at each corner. Each side of the Square is about one and a half to two fists wide, if you hold your fist at arm’s length against the sky and measure across the widest part.

5) From the corner star that is farthest north, look for two chains of stars curving north. Not counting the corner star, there are three bright stars in each chain.

6) The corner star, although part of the Great Square asterism, is technically in Andromeda. Its name, Alpheratz (AL-fuh-rats) sounds like a lab experiment gone terribly wrong, but it’s Arabic for horse’s shoulder, a reference to Pegasus.

Along the lower chain— the one closest to the eastern horizon— the star to the left of Alpheratz has no traditional name, so we call it Delta, its star catalog designation. Next in line is Mirach (MIRR-ahk), Arabic for girdle. Mirach and Alpheratz are tied for the title of brightest star in Andromeda. Mirach is a red giant; compare it visually to blue Alpheratz. Can you see the difference in hue?

Last in line on the lower chain is Almach (ALL-mahk). Almach is from the Arabic for caracal, a nocturnal cat found in Africa and Asia.

7) Let’s jump to the upper chain, again starting at Alpheratz and moving left. All three stars of the upper chain have no traditional names, so we use their star catalog designations and call them Pi, Mu, and the exceptionally picturesque 51 Andromeda. Honestly, was there no one in the whole of antiquity who could come up with an appropriate name for the star marking the maiden’s royal right foot?

The Chained Woman, from Johann Bode's 1801 star atlas

I imagine the celestial princess finds it undignified enough that her left foot is permanently associated with a reclusive predator with rodent breath. Maybe it’s been eating those alpha rats.