Monday, February 22, 1999

South of the Valley: Darkness and Light

I went out several times tonight, to look at the conjunction of our two brightest planets. Lovely sight. Although I knew how big a degree of sky was, it never the less surprised me to see just how much sky my eyepiece field of view can be, by looking at the separation, naked eye, between these two planets tonight. My daughter, looking up, asked about observing the moon (sometimes I worry about her ;-). I took out the 10" f/5.6 and threw in a 10.5 mm Meade Research Grade Otho, and showed her the area around Triesnecker, carefully letting her take in the beautiful Rima Hyginus, with its large crater breaking the flow of the shallow valley, and the small chain of craterlets that make up part of its length. Carefully showing her the crater for which the famous rilles are named, we followed in great detail the dashes and slashes that make up the Rimae Triesnecker. She had a wonderful time, and so did I.

So much so, that I came out again later, to look again by myself and take a note or two...

Just south the blackened gash of the Valis Alpes, bound in against the terminator by the Montes Caucasus, throwing deep long shadows eastward... south of the rubble fields and west of Montes Alpes, sits the crater Cassini.

Tonight, the morning sun lit the western mantle of the crater, and the inner rim of the eastern wall. The only other light was on the top rims, encircling the crater, and a few sparse brightened areas on the crater floor. The two inner craters that reside as captives of Cassini stood out like volcanic chimneys, stark with their bright ring-like rims and black cores. Their shadows were responsible for the hidden eastern floor of their parent crater, as was the big crater's high western wall for the darkness around its prisoners.

To Cassini's south, the western slopes of crater Aristillus rose, showing channels, clefts and rubble in intricate detail, while the rest of the crater, and what is perhaps an ancient buried crater wall barely visible as a slight risen partial circle to its north, lay cloaked in increasing shadow. The eastern rim of Aristillus too was in darkness. Moving south, much rubble and disturbed terrain was on the terminator between Aristillus and Autolycus, finally rising abruptly upward at that crater. Autolycus literally rose like a wall at that point. This crater too was a black hole ringed by a delicate ribbon of white light on its rim.

Still south, the peaks toward Palus Putredinis rose in brilliance, alone, with all the Palus is shadow. The entire extent of Rimae Frensel snaked along, cloacked here and there in shadows thrown from the western peaks of Mons Hadley, Santos-Dumont and Promontorium Frensel. In moments of good seeing, the Rimae was sharp, and double.

A bird flew across the field of view, making a small live silhouetted interruption against the cold features of the moon, and causing me to come back to my own planet and look up.

The moon was already shrouded in increasing clouds, drawing to an end another night observing.

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