Tuesday, January 12, 2010

10 tips for Moon watchers: mountain ranges, vast volcanic plains, andmore than 1,500 named craters make the Moon a target you'll return toagain and again.(Beginning observing).

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Blue Moon, originally uploaded by S@ilor.

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The Moon offers something for every amateur astronomer. It's visible somewhere in the sky most nights, its changing face presents features one night not seen the previous night, and it doesn't take an expensive setup to enjoy it. To help you get the most out of viewing the Moon, I've developed these 10 simple tips. Follow them, and you'll be on your way to a lifetime of satisfying lunar observing.

1 Perform a "no optics" survey

The best way to begin your journey as a lunar observer is to learn the Moon's major features. Head out with a simple Moon map, and use just your eyes to identify our only natural satellite's top attributes.

As luck would have it, Stephen James O'Meara's "Secret Sky" column in the January 2010 issue deals with this very point. He gives a detailed description of naked-eye lunar features. Subscribers to Astronomy can visit www.Astronomy.com/OMeara to view this column (and all of O'Meara's columns) online.

2 The Full Moon is for romance

Contrary to what you might think, Full Moon is not the best time to observe our natural satellite, although that's the time when it's at its brightest. When the Moon is full, the Sun lies behind Earth (as we face the Moon) shining directly down on the lunar surface. Shadows are at their minimum lengths, and you can't see much detail. You can still observe the Moon when it's full, but the contrast between its light and dark sections will be better at other times.

3 View the Moon at "prime time"

Two intervals during the lunar "month" (from one New Moon to the next) are best for observers. The first begins shortly after New Moon and continues until 2 days past First Quarter. Amateur astronomers tend to favor this span because the Moon lies in the evening sky.

An equally good observing period starts about 2 days before Last Quarter and goes until the Moon lies so close to the Sun that it's lost in morning twilight. At these times, shadows are longer and features stand out in sharp relief. Another benefit you'll get when you observe the Last Quarter Moon is that the atmosphere before dawn usually appears steadier than it does after sunset. After sunset, a lot of heat remains in the atmosphere. As hot air rises and cooler air falls, the resulting turbulence leads to unstable air--what observers call bad seeing.

4 The terminator will help you

During the two favorable periods described in #3, point your telescope anywhere along the line that divides the Moon's light and dark portions. Astronomers call this line the terminator. Before Full Moon, the terminator marks where sunrise is occurring. After Full Moon, sunset happens along the terminator.

Here you can catch the tops of mountains protruding just high enough to catch the Sun's light while surrounded by lower terrain that remains in shadow. Features along the terminator change in real time, and, during a night's observing, the differences you'll see through your telescope are striking.

5 The best scope for viewing the Moon

Nearly any telescope will do to observe lunar details. You'll get great views of the Moon through a 2.4-inch refractor, an 8-inch reflector, or an 11-inch Schmidt-Cassegrain telescope. Observers with several options (but not a permanent observatory) usually pick a scope they can set up many nights in a row. Observing on successive nights makes it easier to follow the terminator's progress.

6 Cut down the moonlight

Many observers employ either neutral density filters or variable polarizing filters to reduce the Moon's light. I prefer the latter because an observer can change how much light the filter transmits.

Two other methods to reduce the Moon's brightness are to use high magnification or to add an aperture mask. High powers restrict the field of view, thereby reducing light throughput. An aperture mask causes your telescope to act like a much smaller instrument, but at the same focal length.

7 Turn on your best vision

Some years ago, my late observing buddy Jeff Medkeff introduced me to a better way of observing the Moon: Turn on a white light behind you when you observe between Quarter and Full phases. The light should be moderately bright (I suggest something in the 60-watt range), but neither your eyes nor the eyepiece should be in direct view of the fixture.

The addition of white light suppresses the eyes' tendency to dark adapt at night. Not dark adapting causes the eye to use normal daytime vision, which is of much higher quality than dark-adapted night vision. In essence, you'll see more detail because you're viewing with a better part of your eye.

8 Work from a list

One of the best ways to learn the Moon is to undertake an observing project. In the United States, the Astronomical League offers one such project, the Lunar Observing Club. You'll learn a lot about our satellite as you work through a list of 100 lunar features.

To receive a certificate, you must be a member of the league, either individually or through an astronomy club. For details about the club, see www.astroleague.org/al/obsclubs/lunar/lunar1.html.

In Britain, the British Astronomical Association coordinates lunar observing. Visit www.baalunarsection.org.uk.

9 Dig for the details

Of the 1,940 named lunar features, 1,545 are craters. Challenge yourself to see either how small a crater you can detect or how many craterlets in a given area you can observe. You'll need a detailed Moon map for this project.

For the second challenge, you can choose a lunar sea, but usually a large, flat-bottomed crater works best. For example, if you search the large crater Plato, you'll find four craterlets on its floor, each about 1.2 miles (2 kilometers) across. Lunar observers consider seeing these craters a test for a 6-inch telescope.


10 Shoot the Moon

How can a celestial object that's so easy to photograph be so difficult to photograph well? The Moon is large and bright (only the Sun outshines it), and you can use any camera connected to any size telescope to image it. That's the easy part.

But the Moon also contains vast areas of low contrast that have little color differential. Recording those regions so they look like what your eyes see is the hard part.

Luckily, we live in the digital age. Unlike when astrophotographers used film, it costs nothing extra to take 200 images instead of just one. Examine them, throw away what you don't like, change one or more parameters (including the techniques you used to process the images) each time, and shoot some more as you continue to perfect your techniques.

Michael E. Bakich is a senior editor of Astronomy.

When should you observe the Moon?

During the next year, you'll get your best views of the Moon by
selecting dates in the following table. The greatest details will
lie on the sunlit portion of the Moon closest to the terminator.
Point your telescope there for the best views.

In the evening sky In the morning sky

February 16-24 February 3-12
March 17-25 March 5-13
April 16-23 April 4-12
May 16-22 May 4-12
June 14-21 June 2-10
July 13-20 July 2-9
August 12-18 August 30-September 6
September 10-17 September 29-October 5
October 9-16 October 28-November 4
November 8-15 November 26-December 3
December 7-15 December 26-January 2, 2011

Source Citation
Bakich, Michael E. "10 tips for Moon watchers: mountain ranges, vast volcanic plains, and more than 1,500 named craters make the Moon a target you'll return to again and again." Astronomy Feb. 2010: 52. Academic OneFile. Web. 12 Jan. 2010. .

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