Ptolemaeus, Alphonsus, and Arzachel

November 17, 2007

Uploaded 1/7/08

South is up in this image, more info below.

1290 x 960 size

 One of the finest crater trios on the near side of the lunar surface is Ptolemaes, Alphonsus, and Arzachel. (Bottom to Top). The amount of detail in this moderately high resolution image is worthy of further discussion, and I'll start with the big three, then you can work our way around this field. And please take a look at the full sized image, the small thumbnail above is merely a taste of the numerous details of this region.

Lets start with the bottom most crater in this image, or more correctly Ptolemaeus is a "Walled Plain". This is the most ancient crater of the three, and you can see the walls of Alphonsus encroaching on its south side where the two meet. Ptolemaeus is 92 miles in diameter, the same distance of Payson to Phoenix. Along with some ghost craters and tiny craterlets, the floor of this crater is relatively featureless. Of special interest is the 10 mile diameter half ghost crater Ptolemaeus B, located just below the largest small crater in the lower left (NW) quarter. It is half submerged in mare lavas.

Next, and in the center of this image is Alphonsus. This 71 mile diameter walled plain type crater contains a central peak, Also a series if ridges runs in a north south direction through the crater. On the left side, if you look carefully, you can find Rimea Alphonsus, a collapsed lava tube like formation.

The smaller but magnificent crater at the top of the trio is Arzachel. A very deep crater, some 60 miles in diameter has 3000 foot rims, and a 4000 foot tall mountain in the center. The floor of this lava filled crater is very rough, and of special interest is the very well defined rille on the left side, snaking round small craterlets. The name of this beautiful structure is Rimea Arzachel.

Also of special note, look at the numerous gouges in the landscape in a north west - south east direction. These were blasted out when the large crater Copernicus to the north east was formed.

Processing: 70/1000 best frames, MAP 50 alignment in Registax, Regulated Van Cittert Deconvolution in PixInsight Pro, Levels and Contrast Masking In Photoshop CS3, Focus Magic Plugin.

Instrument: 12.5" f/5 with 1.8x Barlow Platform: Astrophysics AP1200 CCD Camera: Image Source DMK 31AU03.AS Filter: Hoya R72 Exposure: 1/60 sec 15fps Location: Payson, Arizona Elevation: 5150 ft. Sky: Seeing Average, Transparency 8/10 Outside Temperature: 35F Processing: Registax, PixInsight Pro, Photoshop CS3, Focus Magic Plugin