Swan or Omega Nebula June 18, 2010 Image © 2010 Darrell Dodge

September Skies
by Dennis Cochran

ast year we visited the many gaseous nebulae bubbling out of the teapot of Sagittarius the Archer. This sky-actor of the Greeks is, like many constellations, a fanciful human-animal mixture, a man-horse armed with a bow which he aims at Antares, the heart of the Scorpion. His bow curves up the right side of the lid and body of the teapot, while the tip of the spout is the point of his arrow.

In September, ‘09 we mentioned the features we see in the spiral arm towards the center of the galaxy that spin in the steam rising from the teapot’s spout, like the Trifid, Omega and Lagoon nebulae. See that write-up for a tour of those famous M-objects. We’ll do the Teapot this time, emphasizing a different set of objects. In September, the line marking the bottom of the teapot is now slanted from northeast down to the southwest. This tilted line harbors several globular clusters: M54 at the left end near ζ (zeta) Sag and M70 halfway down towards ϵ (epsilon) Sag. Sliding beyond M70 we come to the fainter globular, NGC-6652. Upper left from it is M69; below-right of that is the Epsilon star at the lower end of the teapot. While you’re down there, if Sagittarius is high enough in the sky for you to see under him, you’ll find Corona Australis, the Southern Crown, a curved-line constellation a bit like a cup on its right side. The upper-left part of its curve has “a field of bright and dark nebulae and obscuring dust” (Peterson’s Field Guide), featuring NGC objects 6726 and 27, 6729 and the faint glob, 6723.

Now, back at the left end of Teapot’s bottom, if you search mostly east and a bit south below its handle about two handle-lengths, you’ll find the large, loose globular M55, a mere 17,000 light-years away. Then, up to the left of the star λ (lambda) Sag at the top of the lid, we find M22, twice-mentioned here in recent months, with a faint neighbor, NGC-6642 above-right of M22, while another glob, M28 (almost star-like), lies above-right of λ (lambda) Sag. Bouncing back to the Teapot’s bottom, from the right end continue sweeping right, but now level to the horizon, for the large, hazy open star cluster, M7, a binocular object that forms a triangle
with γ (gamma) and ε (epsilon) Sag, the two stars of the teapot’s spout. Globular cluster NGC-6453 is on the right edge of this cluster. To the upper-right of M7 is slightly-smaller M6. These two large star clusters are beautiful objects for smaller scopes. South-southwest of the M7-M6 line are the Cat’s Eyes, the two stars that make up the Scorpion’s tail, being Lambda and Upsilon of that constellation. Now, if you can see the very bottom of the ‘J’ shape of the scorpion, where the body of the scorpion first turns left to start the curve of his tail, there is star cluster NGC 6231, which resembles a miniature Pleiades. This entire rich sky region is in a spiral arm about 5,000 light-years nearer to the center of our galaxy than we are.

Closer to home, Jupiter rules the planets, primarily by being up all night, as Saturn disappears sunward from the scene. When will Jupiter’s South Equatorial Belt return? There is an entire article about this phenomenon in the Sept. S&T, P. 50. Maybe you will see the big comeback as they describe it; maybe it’ll be back by the time you look! You may be able to witness the whole unfolding drama just by looking at Jupiter every evening. And while you’re there, green Uranus lies just a degree above Jupiter, so you can score two gas giants in one field of view. Blue Neptune is still off the left end of joker’sgrin, Capricorn. Don’t look for it on the 19th-
20th when the full moon will be blasting through that part of the ecliptic. The Jupiter- Uranus pair will be blasted on the 22nd.

Comet Hartley will be cruising east through southern Cassiopeia in late September. It comes around every 6.5 years (P. 52 of S&T.)

Meetings: Open House, our monthly public star party, occurs at Chamberlin Observatory on Saturday the 18th, when the waxing moon will be far past 1st quarter. The General Meeting is on Friday the 24th at 7:30 P.M. at Olin Hall at DU, and on Friday, Oct. 1, the E-Board will meet at Chamberlin.

- Dennis Cochran

SOME NOTABLE CELESTIAL OBJECTS THIS MONTH

Description RA DEC Constellation M51 - Whirlpool Galaxy 13h 29.9m 47° 12'  Canes Venatici M106 - spiral galaxy 12h 19.0m 47° 18'  Canes Venatici NGC 5907 - edge-on galaxy 15h 15.9m 56° 20'  Draco M12 - globular cluster (best in Ophiuchus) 16h 47.2m -1° 57'  Ophiuchus NGC 6543 Cat's Eye Planetary Nebula 17h 58.6m 66° 38'  Draco NGC 6207 (Levy 19) small galaxy near M13 16h 43.1m 36° 50'  Hercules M16 - Eagle Nebula 18h 18.6m -13° 58'  Serpens M17 - Swan or Omega Nebula 18h 20.8m -16° 11'  Sagittarius M20 - Trifid Nebula 18h 02.3m -23° 02'  Sagittarius M8 - Lagoon Nebula 18h 03.3m -24° 23'  Sagittarius M57 - Ring Nebula, planetary nebula 18h 53.6m 33° 02'  Lyra M27 - Dumbbell Nebula, planetary nebula 19h 59.6m 22° 43'  Vulpecula M15 - Globular Cluster 21h 30.0m 12° 10'  Pegasus NGC 457 - ET or Owl Cluster 1h 19.1m 41° 16'  Cassiopeia M31 - Andromeda Galaxy (with M32 & M110) 0h 42.7m 22° 43'  Andromeda M33 - The Pinwheel or Triangulum Galaxy 1h 33.9m 30° 39'  Triangulum NGC 253 - Silver Coin or Sculptor Galaxy 0h 47.6m -25° 17'  Sculptor NGC 891 - Outer Limits Galaxy (edge-on) 2h 22.6m 42° 21'  Andromeda   RA/DEC for brightest of multiple objects

References: Observers Handbook 2010, Sky & Telescope and Astronomy magazines - Selected by D.M. Dodge

Comets and Other Special Celestial Events

See Jim Holder's article in the February 2007 Observer for more information about locating comets.