Dawn Patrol   Leave a comment

The Dawn Patrol is proceeding as planned. So far there’s been one observing session that started between 2am and 3am (MST), and the rest have begun closer to 4am. I’m finding it much easier to rise an hour and a half earlier than normal, rather than to stay up until midnight or so, as I did a few days back. Except for a day that involved high winds in the wee hours of the morning, these Dawn Patrol sessions have involved pleasant and beautiful conditions. Little or no wind, and then just light breezes, combined with mild temperatures between 58°F and 65°F. (14°C and 18°C). The skies have been clear and the transparency good, and as the Moon has waned more and more stars are out and easily seen. And it is quiet, very quiet, in the cool pre-dawn hours. The sounds of the city around me are muted, and on this Sunday morning almost inaudible. No voices, no cars on the street, with only a mockingbird singing loudly in the light of the Moon. He is singing less, now, and starting later, as the light of the Moon fades. Now and then a White-winged Dove awakens early. These calls and songs do not banish the morning quiet so much as define it. The awareness of how quiet the world is at such an hour is accented when the Mockingbird’s last note fades.

This morning the lunar terminator was a complicated thing, in mountainous places rough and ragged, with bright arcs of brightly lit stone and black bays of inky shadow where the divide between day and night passes through cratered terrain. It’s easy to think of the lunar terminator as a simple dividing line between lunar night and day, and where it crosses the surface of maria this may come close to the truth. But more often than not the terminator is anything but simple. This morning served as a fine example to prove the point. Half lit craters with shining west facing walls to the north of Mare Frigoris, with the shadows within clinging as much to the north as to the west. Plato broad and dark and smooth, with no sign of craterlets using such modest aperture (102mm) under mediocre seeing conditions. The lunar Alps presented a crazy jumble of gleaming bright peaks in a black matrix made of the mingled shadows at their feet. Farther south the proximity of craters such as Ptolemaeus, Alphonsus, and Arzachel created bulges of shadow reaching to the light of day, and bright broken curves of light where high crater rims and the tips of central peaks were bathed in the light of the setting sun. South to more heavily cratered terrain, where outlines grew more confusing, and the black bays of intruding shadow were smaller and rimmed with silver light.

Observing the Moon is always about tricks of the light. For this morning’s Dawn Patrol, it added up to quite a show.

Posted May 13, 2012 by underdesertstars in Amateur Astronomy

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