December 14, 2013

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Tricky Moon, Slow Learner

NEWS FLASH: China lands on Moon!

image by DANIKXT, Navacerrada-Madrid (Spain)

I liked this double image immediately. The top one was taken only 96 seconds before the bottom image. But then I looked more closely and got confused. The upper image shows the 6 or 7 day old Moon with the terminator just past Copernicus, setting behind some distinctive rocks and foliage. And the bottom image depicts the western limb - see Procellarum and Grimaldi - setting behind the same foliage. But the terminator is near Copernicus, how could the western limb be visible less than 2 minutes later? Were these photos actually taken about 5-6 days apart, with - by skill or luck - exactly the same foreground? Then Dani explained it to me. As the Moon sank behind the foliage the bright part of the Moon went out of view leaving behind the western part lit by Earthshine. The exposure automatically increased (I assume it wasn't manual because Dani took a long series of frames of the Moonset) from 1/200 of a second to 1.3 seconds, and the camera adjusted its sensitivity by a factor of two. That explains the increased graininess, the reduced sharpness, and the pink glow to the back illuminated clouds. Interpretation of images requires care!

Chuck Wood

Technical Details
2013-12-12. Nikon D7000 ED 80 Long Perng 550mm f/6.2 + Barlow x2
Upper Photo: Hour 2:49; exp: 1/200 sec @800 ISO
Lower Photo: Hour 2:51; exp: 1,3 sec @4000 ISO

Related Links
Dani's website

Yesterday's LPOD: Faulty Ideas

Tomorrow's LPOD: Geologic Setting of Chang'e 3 Landing Site


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