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Lunar Surface: September 25th, 2006.


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Universe: September 25 - October 1, 2006.
M57: The Ring Nebula - Credit: C.F. Claver/WIYN/NOAO/NSF.

The Moon is back, but so are studies as we take a great look a planetary nebula this week. Yes, we’ll study lunar features, but let’s not forget variable stars and bright clusters! time to turn an eye towards the sky.

Monday, September 25 - Look for the Moon returning low on the western horizon tonight to spot a phenomenon known as "Earthshine." This is sunlight reflected off our own atmosphere and oceans which faintly illuminates the side of the Moon not receiving direct sunlight. Try to spot some features on the "dark side."

Tonight when the Moon sets, let’s return to some previous studies and have an "Autumn Planetary Marathon." Start easy with M57 between Gamma and Beta Lyrae. Head north-northwest to the "Cat’s Eye" (NGC 6543) roughly between Delta and Zeta Draconis - you’ll need your charts for this one! Now southwest to the "Blinking Planetary" (NGC 6543) - found less than three degrees east-southeast of Iota Cygni. Continue east-southeast a little less than 6 degrees past Deneb to the "Box Planetary" - NGC 7027. Now on to the brightest of the ten - M27. The "Dumbbell Nebula" is located a little more than 3 degrees north of Gamma Sagittae. Now drop two hand spans south to the "Little Gem" (NGC 6818) - around 7 degrees northeast of Rho Sagittarii.

One hand span east of the "Little Gem" leads you toward the "Saturn Nebula" in Aquarius - a little more than a degree west of Nu. Now it’s a huge jump of more than two hand spans west-northwest to tiny NGC 6572 - located around two finger-widths south-southeast of 72 Ophiuchi. Continue on to compact NGC 6790 a finger-width south of Delta Aquilae. Did you find them all? Well, if the "Cat’s Eye" is the toughest to locate, then NGC 6790 is the hardest to identify. Good going! But don’t stop now... Two hand spans west-northwest leads to NGC 6210 - best located using pointer stars Gamma and Beta Herculis. Ready for the finale? Then remember you recent instructions and locate "the Blue Snowball" - NGC 7662. Excellent work!

Tuesday, September 26 - Tonight’s slender crescent Moon won’t last long, so let’s use the time to advantage and take on a deep sky study.

The journey might seem like a simple one, but the rewards are great. Start by identifying bright Beta Aquarii about a fist’s width above the northeasternmost corner star of Capricornus. Continue northward another five degrees, because we’re going to introduce you to M2.

First seen by Maraldi in 1746 and later cataloged by Messier in 1760, M2 is easily seen in binoculars and small telescopes. This compact globular cluster is around 50,000 light-years away in the general direction of our galaxy’s southern pole. Containing more than 100,000 stars (including some red and yellow giants) even small scopes will immediately pick up on M2’s intensely bright core. But it will take larger scopes - and higher power - to resolve the many faint 14th to 15th magnitude members of this distant Class II globular study.

Wednesday, September 27 - Tonight on the lunar surface, begin by identifying Mare Crisium and head north for previous study Cleomides. About two Crisium lengths further northwest, see if you can identify crater Endymion. This expansive crater will appear to have a brilliant west wall and deep shadow to the east. While it will look much like its surroundings, watch over the days ahead as its lava-filled floor darkens considerably.

Now let’s study a very impressive variable star. Eta Aquilae is one of the most fascinating stars in the sky to watch and it doesn’t even require a telescope. Just look less than one fist-width due south of Altair...

Discovered by Pigot in 1784, this Cepheid variable has a precise cycle of nearly a magnitude shift every 7.17644 days. During this time Eta reaches a maximum of magnitude 3.7 and declines slowly over 5 days to a minimum of 4.5. Yet it only takes two days to brighten again! This expansion-contraction cycle makes Eta very unique. To help gauge its changes, compare Eta to Beta on Altair’s same southeast side. When Eta is at maximum, it will be about equal in brightness.

Thursday, September 28 - Tonight east meets west on the lunar surface as we head for another beautiful crater. Look to the northern tip of Mare Fecunditatis where it joins the eastern extremity of Mare Tranquillitatis. Here you will see the awesome structure of well-worn crater Taruntius. Appearing as a bright ring, remember this location because when the Moon is full, Taruntius’ incredible ray system will stretch for hundreds of kilometers across the lunar surface. Be sure to have a look at the field stars around the Moon, because tonight it will occult Antares! Be sure to check IOTA for precise times and locations for this "don’t miss" event.

While waiting on Antares to reappear, let’s head northeast to observe 6.9 magnitude, mid-sized open cluster - M52. Discovered by Messier on September 7, 1774, you can discover it by drawing line between Alpha and Beta in western Cassiopeia and extending it three finger-widths on the same trajectory. Viewable in binoculars, this fine grouping of fainter magnitude stars is a real treat for the scope. Larger aperture will reveal as many as a hundred stars peeping out against a rich Milky Way field.

Friday, September 29 - Tonight on the lunar surface, let’s start by identifying Mare Nectaris, then head for its south shore. Look for a U-shaped "bay." There you will catch the ruins of Fracastorius. This feature is subtle and you will see little more than a faded white outline. Perhaps at one time during Fracastorius’ evolution, its walls were melted away by lava flow. At high power you may spot some low hills and craterlets. Binoculars should resolve Fracastorius as a full ring.

Return to confirm M52 tonight, then head less than a finger-width southwest to locate open cluster NGC 7510 in Cepheus. Although this small, 7.9 magnitude cluster is beyond the range of binoculars, its brightest half dozen 12th magnitude stars give a wedge-like appearance in modest Telescopes at higher magnifications.

Saturday, September 30 - Today in 1880, Henry Draper must have been up very early indeed to take the first photo of the Great Orion Nebula (M42). Although you might not wish to set up equipment before dawn, you can still use a pair of binoculars to view this awesome nebula!

Tonight on the lunar surface, take a close look at Mare Serenitatis and its south-southwest border. These are the Haemus Mountains. Look in their midst for the sharp punctuation of Class I Menelaus. This small crater has a brilliant west inner wall and deeply shadowed floor. Like Taruntius, Menelaus is another fine crater to watch for expansive ray systems as the terminator progresses.

Even with the Moon, we can turn binoculars northwards to very large open cluster IC 1396. Using very low power in telescopes, you will see a thickening of stellar density over a three full-moon sized region of numerous 8th and fainter magnitude stars just south of Mu Cephei.

Sunday, October 1 - In 1897, the world’s largest refractor (40″) debuted at the University of Chicago’s Yerkes Observatory. Also today in 1958, NASA was established by an act of Congress. More? In 1962, the 300-foot radio telescope of the National radio astronomy Observatory (NRAO) went live at Green Bank, West Virginia. It held place as the world’s second largest radio scope until it collapsed in 1988.

Tonight let’s visit with an old lunar favorite. Easily seen in binoculars, the hexagonal walled plain of Albategnius appears near the terminator about one-third the way north of the south limb. Look north of Albategnius for even larger and more ancient Hipparchus giving an almost "figure 8″ view in binoculars. Between Hipparchus and Albategnius to the east are mid-sized craters Halley and Hind. Note the curious relationship between impact crater Klein on Albategnius’ southwestern wall and that of crater Horrocks on the northeastern wall of Hipparchus. Now let’s power up and "crater hop"...

Just northwest of Hipparchus’ wall are the beginnings of the Sinus Medii area. Look for the deep imprint of Seeliger - named for a Dutch astronomer. Due north of Hipparchus is Rhaeticus, and here’s where things really get interesting. If the terminator has progressed far enough, you might spot tiny Blagg and Bruce to its west, the rough location of the Surveyor 4 and Surveyor 6 landing area. Directly north of Rhaeticus will be a long series of surface "cracks" known as rimae. These particular ones are the Rimae Triesnecker and you will see the crater itself just to their west.

Once lunar studies are complete, turn the scope north and have a look at a fine open cluster. Visible in binoculars most nights, 6.4 magnitude NGC 7243 will show more than two dozen of its brightest 10th and 11th magnitude members through the average scope and as aperture increases - so does the stellar population. You’ll find it less than 2 finger-widths west-southwest of Alpha Lacertae.





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