For observers living in mid-northern latitudes, Sagittarius the Archer never climbs very high in the sky. From my home it's often obscured by trees. But in early September this distinctive, teapot-shaped pattern of stars stands highest in the south as soon as it gets dark. Shining at eye level and finally free of the foliage, it's hard to ignore.
If you live where it's really dark, finding Sagittarius is easy. Just follow the slant of the Milky Way down toward the southern horizon to a bigger and brighter patch called the Large Sagittarius Star Cloud (LSSC). The Teapot sits just to the left (east) of the cloud, which resembles a blast of steam from its spout.
Not only is the LSSC the brightest chunk of the entire Milky Way, it's also the most remote region of the galaxy visible with the naked eye. We look inward toward the Milky Way's center when we gaze at the cloud, where oodles of old, orange giant stars congregate. If you've taken time exposures of the Milky Way, look again at the cloud, and you'll see that it glows yellow, a reflection of its older stellar population compared to the flat disk of the Milky Way, which is richer in younger, bluer suns.
When you see the Teapot, you're also facing squarely toward the center of the galaxy. Cosmic dust shed by multiple generations of stars obscures the core from view in ordinary light. To get around that blockade, astronomers use telescopes that can see in the infrared (beyond red) and radio waves. Their longer waves penetrate the dust and allow us to peer inside.
What they've found there is an enormous black hole called Sagittarius A* (pronounced Sagittarius A-star) about 14.6 million miles across (166 "Jupiters" wide) and four million times as massive as the sun. Stars and gas clouds orbiting near this gravitational dungeon zip around it at breakneck speeds.
Grab your binoculars and a folding chair and take a drive to the countryside the next clear night before Sept. 12, when the moon returns. While lying on your back, you can explore the Large Sagittarius Star Cloud and for that matter, the full band of the Milky Way, in comfort. You'll be stunned by what you see. There are additional smaller star clouds, clumpy bright star clusters and nebulae. And stars. Lots and lots and lots of stars. Astronomers estimate our galaxy contains between 100 and 400 billion of them.
Sagittarius is an ancient constellation that originated with the Sumerian civilization in Mesopotamia, which flourished between about 4,500 and 1,800 B.C. Back then, they connected the starry dots into their god of war and hunting named PA.BIL.SAG, a part-horse, part-human archer with wings. Later, the Greeks adopted the constellation but dropped the wings and associated the figure with Crotus, a satyr who invented the hunting bow.
What we see as the Teapot actually represents a bow and arrow, with assorted fainter stars off to the east and south outlining the horse's rump and legs. Sagittarius has been a teapot in my mind for so long I've never once imagined it as a hunting implement. But you can see from the mythological depiction above that it bears an uncanny resemblance to one. The next clear night, I'm going to open my mind to this new view. By the way, the arrow just happens to point almost directly at the center of the galaxy.
One of the most inexplicable things about Sagittarius is why its Alpha Star, the name typically given to a constellation's brightest member, is actually the 15th brightest. Both Alpha and neighboring Beta Sagittarii are faint 4th magnitude stars, while the brightest is Epsilon at magnitude 1.8 followed by Sigma (Nunki), at 2.1. What gives?
According to Ian Ridpath, English author and astronomy popularizer, it appears that the ancient Greek mathematician and astronomer Ptolemy got it wrong in his landmark astronomical treatise called the Almagest. He described Alpha and Beta as second magnitude stars. Persian astronomer Al Sufi corrected the error in his Book of Fixed Stars, written around 964 A.D.
Unfortunately, the German astronomer Johann Bayer, who systematically named the stars using the Greek alphabet system still in use today, ignored Al Sufi's corrections and retained Ptolemy's original designations. In his 1603 atlas Uranometria, he labels them Alpha and Beta and draws the stars much brighter than they actually are.
And that's how two faint, nondescript stars that almost no one can see from light-polluted skies became the "brightest" stars of Sagittarius. Now that you know a little bit of history, both ancient and recent, face south the next clear night around 9-9:30 p.m. local daylight time and enjoy a steamy cuppa.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.