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Quarter Moon





Among astrophotographers, I suspect that our moon is a seen as a bit too common to spend much time on. After all, we can observe it with the naked eye - why waste precious minutes on it when we can be chasing down some truly weird objects out there in the universe?  And yet, I find that I come back to it quite often, either for a photograph or, more often, just to consider it's many features through a decent telescope or set of binoculars. There is still something beguiling about getting up close and personal with all those craters.

There are quite a few interesting features visible in this image. Three of my favourite craters - yep, I'm a guy who has "favourite craters" - are right in the middle of this image of the moon. Ptolemaeus (the larger one), Alphonsus (middle), and Arzachel (top, smallest) form a slightly curved line running along the day/night terminator. You can see a clearly defined central peak in the middle of Arzachel, and another that is a bit harder to make out in the middle of Alphonsus. These peaks are reasonably common amongst lunar craters between 15 km and ~120 km in diameter. Arzachel and Alphonsus are at the top end of this range, at 96 km and 119 km diameter, respectively (Ptolemaeus is 153 km wide, so no peak). These pointy mountains are created in the initial impact, which has such force that the central rock rebounds upwards much like the water does when a pebble is dropped into it.

In the bottom left quadrant, we see some larger and smoother expanses. These are "seas" or mares, so-called because pre-telescope civilizations believed them to be large bodies of water. The larger, middle one, which has a more blue-gray appearance, is Mare Tranquillitatis (Sea of Tranquillity); the site of the first lunar landing.



















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