Jimmy Westlake: Getting acquainted with Aquarius
October 31, 2016
With the moon out of the way this week, it's a great time to step outside after nightfall and look for the large but faint constellation of Aquarius, the Water Bearer.
Aquarius is the 11th constellation of 12 in the Zodiac and the 10th largest of our 88 official constellations.
The Greek astronomer Ptolemy listed Aquarius as one of his 48 constellations in the second century AD, but its place in the stars predates Ptolemy by a thousand years or more, to the early Babylonian culture.
Aquarius occupies a spot in the sky alongside many other watery constellations, a patch of sky known as the "celestial sea." It is bounded by Capricornus the Sea Goat to the west, Pisces the Fish and Cetus the Whale to the east, Pisces Austrinus the Southern Fish to the south and Delphinus the Dolphin to the north.
Greek mythology identifies Aquarius as the young boy Ganymede, whom Zeus kidnapped from Earth and carried to Olympus to serve as cupbearer for the gods.
Although Aquarius contains no bright stars, it does contain a very distinctive pattern of four stars dubbed "the water jug" that looks like a tiny wishbone or letter "Y." My astronomy students like to call it "the flux capacitor," a reference to a magical little device from the popular movie "Back to the Future." It is small enough to fit behind your thumb, held out at arm's length.
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From out of the water jug flows a stream of stars that splits in two and then converges again just before reaching the bright star Fomalhaut, far to the south. Fomalhaut belongs to the neighboring constellation of the Southern Fish.
Look for the four stars of the water jug around 7:30 p.m. about halfway up from the southeastern horizon and the zenith. The lone bright star Fomalhaut will be straight down below.
Of all of the deep sky objects in Aquarius, my favorite is the spectacular globular star cluster Messier 2, or M2, for short. This ancient swarm of stars lies 33,000 light years from Earth and contains hundreds of thousands of individual stars.
Through binoculars, M2 resembles a fuzzy dandelion head. It takes a telescope to begin to resolve the fuzz into stars. In my 8-inch Celestron telescope, I can see stars to the very center of the cluster. Nineteenth century British astronomer John Herschel aptly described M2 as looking "like a heap of fine sand."
Also within the borders of Aquarius is the beautiful Helix Nebula, a spiral of colorful gases ejected by a dying star, thousands of years ago. The Helix Nebula is only 695 light years from Earth — a stone's throw, compared to M2.
Aquarius sends us several meteor showers each year, but the best of them for Northern Hemisphere observers is the Eta Aquarids, seen annually in early May.
The Eta Aquarid meteors are pieces of Halley's Comet that rain down into Earth's atmosphere each year when Earth crosses the comet's orbital path. When the meteor shower peaks, on the mornings of May 5 and 6, a single observer might spot 20 Aquarid meteors in an hour of sky watching.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Steamboat Springs Campus. His “Celestial News” column appears weekly in the Steamboat Today newspaper. Check out Jimmy's astrophotography website at jwestlake.com.