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Urban Observing December 2012 November 30, 2012

Posted by aquillam in Astronomy.
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We start the month with a waning gibbous Moon. Go out around 9 PM on Dec 1 and point a small ‘scope a little south of mid-way along the terminator to get a nice view of the highlands that divide Mare Fecunditatis (Sea of Fertility) and Mare Nectaris (Sea of Nectar.) It’s not really much of a boundary between the two, but that’s actually a bit of an advantage, because the dark mare basalt helps highlight the bright highland mountains. Head farther north along the terminator and you’ll see the eastern edge of Mare Serenitatis. Some of the mountain tops along the mare rim will be bright lit while the land they rise from is in shadow.  This is the view Galileo had early in his observations of the Moon that prompted him to claim that the Moon not only wasn’t perfect, it was covered in mountains.

If you’re an evening observer, you’ll have to wait until December 17 to catch the Moon at 9 PM again. The terminator wil be on the other side of Mare Serenitatis that night, so you can catch dawn on the mountains to the east of the Mare! December 19 is the night to look if you’re a fan of Tycho. The crater is just inside the lit area on that evening.One can almost get lost in the jumble of craters in the southern highlands.

Want some more lunar landmarks? Check out the Full Moon Atlas,  http://www.lunasociety.org/atlas/index.shtml.

For bright evening objects, December features Jupiter in addition to the bright winter stars. Jupiter is at opposition on Dec 2, which means it rises at sunset, so it’ll be well up by 8 or 9 PM for the entire month. Being in opposition also means being in retrograde, so it will move slowly east through the Hyades. Look for a conjunction with the almost full Moon on December 25 (what a great chance to try out that new ‘scope you got!)

December is a great month for having a lot of things to observe, though it is generally a lousy month for clear skies.

At 9 PM on Dec 1 you’ll find the summer triangle in the west. It’s a good chance for a last look at Albireo. Of course if you miss it, you can still get out at 6 PM on Dec 30, though it will be darker the week before.

Overhead and to the south at 9 PM are the fall constellations, Cassiopea, Andromeda, Pegasus, and Perseus (among others.) If you have a telescope, the Perseus double cluster is a good target even for fairly light polluted skies. The Andromeda Galaxy is also in this area, though it’s a tough catch in the city. If you have some decent light blocking around your telescope, it’ll probably just look like a smudge on the otherwise grey sky. Point sources are easier of course, so be sure to look up eclipse times for Algol. If you’re within a few hundred miles of Ann Arbor, watch it on the evening of December 11, between about 7 – 11 PM/ Mid eclipse should be at 9:18 PM.

Look farther west for the winter stars, just rising at 9 PM on Dec 1, or well up in the east and south on Dec 30. Orion is unmistakable, and has the lovely red-blue combination of Betelgeuse and Rigel. The top belt star, Mintaka, is on the celestial equator. Also in the area are the red giant Aldeberan, golden Castor, and brilliant Sirius. The Orion nebula is one of the few star forming regions you can generally see easily even in the city, though you will need a telescope. Also point that ‘scope (or a nice pair of binoculars) over at the Pleiades.

If you’re a morning observer, you start the month with a real treat. Saturn, Venus, and Mercury all lined up in the morning sky, just under Spica. Be sure to set your alarm on December 11, when the crescent Moon joins the group, in close conjunction with Venus.  The closest new moon of the year falls on December 13, so this will be one of the largest crescents of the year too (though it’s really such a tiny difference you’d have to measure carefully to tell!)

If you’re up for a challenge  we have an unusual event this month. Usually, there is a day when the Moon is New and therefore isn’t visible. This month however, the New Moon is early on the 13th for observers in North America. If you have a clear SE horizon and a pair of binoculars, you can go out just before dawn on the 12th to view the very old Moon, then go out just after sunset on the 13th and look SW for the very young Moon. These will be tough, even with binoculars.

In the mornings around December 20, look low in the east an hour before sunrise to catch the last of Mercury, along with the red supergiant Antares. The 20th is also when Venus and Mercury are closest to each other.



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