August 24, 2017
Originally published February 5, 2008
left images by George Tarsoudis, Alexandroupoli, Evros, Greece; right images from NASA AS15-M-2075. Back away from your screen and squint your eyes to improve the view of the enlargement.
It is surprising how many gaps there are in our knowledge of the Moon. Even rudimentary knowledge such as how big something is. George noticed that in the Moon-Wiki page for the Diophantus Rille there was no width given, it was simply said to be narrow. George was curious and asked: How narrow? So he used the LTVT tool to measure its width on his image, finding a value of 830 m. Then he measured it in six different locations on the splendid Apollo image and found values ranging from 410 m to 630 m, with an average of 525 m. Why the difference? Two reasons. First, its harder to measure accurately on a lower resolution image. Second, rilles are constant width, perhaps he measured a place where the rille was widest. In any case, this is a narrow rille, and its remarkable to image even pieces of it with amateur telescopes. I just noticed that the Moon-Wiki page does not include a depth for the rille...
18 Jan, 2008, 18:47:47 UT. 10" at f/6.3 + DMK 21AF40 with barlow projection + filter green, Registax, PS
Rükl plate 19
More on measuring the rille
Yesterday's LPOD: Four Rings and a Mystery
Tomorrow's LPOD: Circles Galore