March 6, 2012
Nodding Shape-Shifter
image from NASA GSFC Scientific Visualization Studio, annotated by Phil Plait
Using LRO altimetry data, scientists at Goddard Space Flight Center in Maryland created an applet - an online phase calculator - and a video of hourly changes of the Moon's appearance for all of 2012. Similar capabilities exist in the iPad app Moon Globe HD and a few others. The GSFC video compresses a year into 2 minutes, 48 seconds and although the main effect is the changing of phase, what is more entrancing is the up and down rotation due to the monthly libration. It immediately is obvious by watching the Moon rotate that Mare Crisium moves toward the north pole and then back again. If you put it on HD and full screen modes it almost make you - or at least me - dizzy. Less conspicuous is the slowly increasing and decreasing of the Moon's diameter as its elliptical orbit pulls it closer and then carries it further from Earth. This is a nice demonstration for astronomy talks. Perhaps someday the applet will work for any date so we can see exactly what the Moon looked like when Galileo and other early lunar sketchers recorded their observations.
Chuck Wood
Yesterday's LPOD: Lunar Mosaic of the Day
Tomorrow's LPOD: Petrographic Map
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