The Straight Wall (Rupes Recta) on the Moon

Jan 5

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1/5/2014 10:00 PM  RssIcon

On January 9, 2014, the Moon will be about 68% illuminated for the Americas. The terminator - that is, where the shadow of the Moon begins and sunlight ceases - is the best place to view the lunar surface with a small telescope. The shadowing makes for dramatic-looking surfaces, and the detail seen is incredible. Because the Moon continues to orbit the Earth every 29.5 days, that terminator shadow moves across the Moon. As more lunar surface is bathed in sunlight, the details become washed out, and the new terminator details are the places to look.

But on Thursday, a well known surface detail colloquially known as the "Straight Wall" (or more scientifically, Rupes Recta) will be both lit and shadowed in Mare Nubium, somewhat between and west of the craters Arzachel and Purbach. This large chart of the Moon shows the location when viewing with a more wide-field view of our natural satellite:

68% illuminated lunar disk showing Rupes Recta (Straight Wall) and other features

For more detail, check out this image that shows a closer view of the Straight Wall. Keep in mind, this "wall" is 68 miles (110 km) long, approximately 1.5 miles (2.5 km) wide, and only about 800 to 1,000 feet (240 - 300 m) high. Although it appears to be a steep slope, this is an artifact of the low Sun angle. The actual slope is only about 7 degrees. 

Because the Moon is a bright object, a telescope can be pushed beyond normal "maximum magnification" limits of 50x per inch of aperture, provided that the atmospheric seeing is steady enough to allow for crisp, clear images at the eyepiece. Otherwise, limit magnification to 150x or so, and note this unusually "straight line" on our Moon.

Get more info on observing the Moon here or check out other objects you can see this week in the night sky with a telescope.

Straight Wall / Rupes Recta detail area

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The Nightlight

This blog includes what to see in the night and daytime skies, thoughts on telescopes, binoculars, and other astronomy observing accessories and equipment, plus my own occasional notes on objects I've seen and observed. Oh, and the random theater or other "my take on life" post. In other words, there is always something interesting. Check it out.