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Vallis Snellius, July 11 2013 July 11, 2013

Posted by aquillam in MichiganAstro, Urban Observing.
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You’ll need a pretty good telescope for this.

A young Moon provides a good opportunity to look at the Vallis Snellius, near the southeastern limb of the Moon. It is the longest valley on the Moon, but it’s usually pretty hard to see because it in relatively shallow and runs east-west, so the shadows don’t stand out well. With a moon that’s only a day or two old, the shadows are at their longest, and it’s you best chance.

Start by finding crater Petavius. It has a well defined central peak and a crack it the floor, so it’s pretty easy to identify. The crack points to a mid sized soft-edged crater that still has a hint of a peak, but is obviously old. If you keep going, you’ll see anothe crater, about the same size, but much fresher (more sharp edged). Go back to that old crater.  That’s Snellius. Now look along the southern edge, and you may notice that the crater cuts across a bit of a depression. That’s Vallis Snellius.

If you find the hunt for Vallis Snellius too frustrating, head back up to Petavius and notice all the other cracks in the crust around it.

If it’s too cloudy tonight, mark your calendar for August 9 & 10. You’ll have a nice shot a Venus again too. You might also try July 16 and August 14, when dusk falls on Vallis Snellius.

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