FINDING THE PAST

LPOD-Mar13-09.jpg
image by Milton J. Aupperle, Calgary, Alberta, Canada

While processing this razor sharp image of the Philolaus region, Milton detected a possible more ancient ring under it. This is an area blanketed by ejecta from Imbrium, accounting for all the shallow, filled in craters, and the paucity of old medium sized ones. There definitely are craters buried to different levels -for example, the one under the blue words Crater Rim is just barely detectable. But is the outline drawn by Milton a likely ancient crater or just a collection of arcuate parts that our eyes assemble into a non-existent feature? As we learned decades ago the best way to interpret the limb is by looking at images from overhead. That is now easy to do with the online USGS Digital Atlas. Sheet 3 shows that the area outlined in blue is the wrong shape to be a single crater and in fact, is two battered craters that actually have designations, Philolaus D at top and C below. Ironically, I may have been the one to assign those letters back in the 1960s, but its too late tonight to find the old maps to see when the designations appeared. I could not answer Milton's question just looking at his images because the foreshortening distortion makes if difficult to identify craters near the limb. That is why many of the old letters (and occasionally names) of limb features had to be deleted when overhead images became available in the 60s.

Chuck Wood

Technical Details
2009 March 6, 22:58:32 Mountain Standard Time from Calgary Alberta. Celstron 8", 5,000 mm focal length with Televue 2.5x, 1384 x 1036 pixel Grasshopper 16 bit FireWire 800 camera with Green filter. Astro IIDC for image capture, stacking, and image processing. Best 108 frames out of 750 frames selected and then 103 MAP selections used for final alignment.

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