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June 17, 2024

Backyard Astronomy: Sagittarius, The Hunter's Teapot (2003-07-21)

By Cheryl Haimann

The next constellation along the ecliptic is a challenge for the backyard observer, but also one of the most rewarding parts of the night sky. In fact, it holds nothing less that the heart of our galaxy.

Remember the Arrow, Sagitta, from the Summer Triangle, and you will not be surprised to learn that Sagittarius is an Archer. The constellation is also traditionally represented as a centaur, the head and torso of a man attached to the body of a horse. Do not call this constellation THE Centaur, though. That honor belongs to Centaurus, a southern constellation only partially visible from northern latitudes.

If that isn't complicated enough, consider that Centaurus and Sagittarius are both identified with the mythological centaur Chiron. Unlike his testosterone-dominant comrades, Chiron was a sensitive new-age centaur, kind and wise, so it seems unlikely that this arrow-wielding hunter is an appropriate representation of him. To get around this problem, some ancients suggested that Chiron created Sagittarius (in his own image, apparently) to guide Jason on the good ship Argo.
That's all academic, though. These days, even serious astronomers identify Sagittarius by looking for an asterism shaped like a teapot, just to the left of the stinger of Scorpius. Between dusk and midnight, Sagittarius moves from the southeast to the south. The entire teapot lies below the ecliptic, which is already near is lowest point for the year, and while the stars are not faint, they are not especially bright, either. Trees or sky glow from city lights will completely obliterate them. You will need a clear southern view in a dark location to fully appreciate the teapot.

Once you have found that dark, clear location, though, the beauty of Sagittarius becomes apparent. The Milky Way is wide and bright here, completely encompassing the teapot and reaching almost to Antares in Scorpius. Sometimes it is described as "steam rising from the teapot." That steam continues overhead, through the Summer Triangle and on to the northern horizon. A quick sweep with binoculars will show that the Milky Way, and particularly the Sagittarius region, is packed with stars. Indeed it is, for just above the teapot's spout is the center of our galaxy.

This dense area is full of not just stars, but also star clusters and nebulae. When French comet hunter Charles Messier built his list of "Things that are NOT comets" in the 1700s, he spent a lot of time documenting the fuzzy bits in Sagittarius. 15 of the 109 Messier objects are in Sagittarius, and several of them are visible with binoculars. Some of the easier objects to find are M6 and M7, two star clusters midway between Scorpius and Sagittarius; M8 (Lagoon Nebula) and M20 (Trifid Nebula), up from the teapot's spout and close enough to see both in the field of view of standard binoculars; and M22, a globular cluster above the handle.

You may have to take a road trip to see Sagittarius and the Milky Way, but this is the perfect time to do it. The Moon is at third quarter on Monday. The waning crescent moon is smaller and rises later each morning, until new moon on July 29. Starting about Wednesday, the slender moon plus the Milky Way's position in the sky mean that the next week and a half will be the best Milky Way viewing opportunity of the year. Prime viewing time is from about 10:30 PM until 1:00 AM.

As long as you are at that dark location, look for Mars rising in the east-southeast shortly after twilight. Or, if you are more of an early riser, Mars will be shining brightly in the south before sunrise.
Article © Cheryl Haimann. All rights reserved.
Published on 2003-07-21
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