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The Sky This Week, 2011 October 4 - 11

A night to look over the Moon

Lunar Southern Highlands, 2011 FEB 13
including the prominent craters Tycho (top center),
Clavius (center left) and Moretus (center bottom)
imaged with a 20-cm (8-inch) Schmidt-Cassegrain telescope.

The Moon brightens the evening sky this week, waxing from First Quarter to Full Moon on the 11th at 10:06 pm Eastern Daylight Time. October’s Full Moon is most popularly known as the Hunter’s Moon because of its similar geometry to last month’s Harvest Moon. In northern latitudes Luna seems to rise at nearly the same time each night for evenings surrounding the Full phase, shedding a little extra bit of light during twilight activities. In September this helps farmers bringing in their crops; in October it helps hunters as they pursue game across the stubble of the harvested fields. The Moon spends most of this week in the barren star fields of Capricornus, Aquarius, and Pisces. On the evening of the 5th she passes just over a degree south of the third-magnitude star Dabih. This is the brightest body she’ll encounter until the week’s end, when she closes in on the bright glow of Jupiter.

It is often said among amateur astronomers that the Moon is "looked over, then overlooked" by owners of small telescopes. Luna is almost invariably the first thing owners of new telescopes look at because she’s very easy to find and offers an amazing array of landscapes to explore with virtually any size telescope. Despite this, though, after awhile people lose interest in our only natural satellite because things don’t change very much. The Moon we look at today is essentially identical to the one first glimpsed by Galileo over 400 years ago. However, getting to know the Moon’s topography can lead to hours of enjoyment at the eyepiece, and every increase in telescope aperture brings finer details into focus. Of all the objects in the solar system Luna provides the most detail that once can see from the surface of our life-giving Earth, and careful scrutiny over time will reveal some truly fascinating landforms that play jet-black shadows on the Moon’s silvery surface. From the seemingly smooth plains of the so-called lunar "seas" to the tortured jumble of craters that define her "highland" regions subtle details abound for those with the patience to look for them. Through a modest six- or eight-inch telescope surface details as small as a kilometer can be seen when the atmosphere is very steady. On this scale the larger craters are truly enormous, spanning dozens of kilometers across. The objects that excavated these great gouges were once endemic to the inner solar system, battering all of the planets during their formative stages. With virtually no erosion, this early record of bombardment has shaped the Moon’s surface into the one we see today. If you have a telescope, join a world-wide program to gaze at the Moon and invite your friends and neighbors over for a look. October 8th is the second annual International Observe the Moon Night (InOMN); visit their website for a variety of activities and suggestions of things to look for on the only other world ever visited by humans.

After you’ve given the Moon a good going-over, take a little time to turn your attention to the bright glow of Jupiter, which now rises before 8:00 pm. The first thing you’ll probably notice is that the apparent disc of the solar system’s largest planet is about a big as a typical crater on the Moon, but careful scrutiny and steady air will begin to reveal details on that faraway disc. Two dusky belts may be glimpsed in small telescopes, and these belts become more structured as aperture increases. So too does the number of smaller belts and brighter zones, each of which marks the presence of a powerful jet stream in the jovian atmosphere. What the view of Jupiter lacks in size is made up for by number; four large moons circle the planet providing a constantly shifting configuration.

If you’re up before dawn, look for the distinctive ruddy glimmer of the planet Mars. He’s quite easy to spot high in the east between the Twin Stars of Gemini, Castor and Pollux, and Regulus, the heart of Leo the Lion. Mars is drifting eastward through the faint stars of Cancer; he’ll pass just north of Regulus in another month.

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