The Ptolemaeus, Alphonsus, Azarchel Crater Chain



As First Quarter comes on, the Lunar observer's eye is inevitably drawn to the center of Hecate's disk, and this "chain" of three great circular formations. Ptolemaeus (158Km), Alphonsus (121Km), and Arzachel (100Km). One of the attractions here is the different appearances of the three. Ptolemaeus' lava-flat floor is littered with small craters. Alphonsus' bowl has also been filled with lava, but there's a central peak, a very interesting rille, and what appear to be wrinkle ridges to marvel at. Arzachel's floor is less smooth still, and also features a rille and a prominent central peak (Alphonsus' peak is a mere nub in comparison). As you might guess from their appearances, Arzachel is the youngest at around 3.2 billion years ("Copernican"). Alphonsus represents the Nectarian period (3.8 - 3.9 billion years). Old Ptolemaeus comes from Pre Nectarian times (4 - 4.5 billion years).

After a winter with little opportunities for (or seeing to support) Lunar imaging, I was finally able to get out and get this shot despite a lack of really optimum seeing. This was takn with the Nexstar 11 GPS (alt-az mode) and a Celestron Neximage webcam. Processing was with Registax 4 and Paint Shop Pro. The two images that compose this picture were assembled with the excellent freeware program, iMerge.


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