Earth's Libration Visualized For the First Time Above the Moon's Far Side

StartsWithABang writes Thanks to the fact that the Moon is tidally locked, we can only see 50% of its surface on any given night. Over time, the fact that the Moon's orbit is elliptical, and that it moves faster at perigee and slower at apogee means that up to another 9% is visible over the course of many years. The observed "rocking" and growing/shrinking of the Moon over time is known as lunar libration, an incredibly interesting phenomenon. But now, for the first time, we've been able to visualize how the Earth appears to move as seen from above the far side of the Moon.

Comments

Early analog work from the 1960's

[Cliff Stoll]

From 1964 through around 1975, planetary astronomers at Tucson's Lunar & Planetary Laboratory used physical models to project and remap the moon's surface. They took high resolution photos through an earth based telescope, and then projected the images onto a spherical, white plaster globe. By carefully controlling the geometry, and knowing distances, angles, and (yes) lunar libation, they created detailed maps of the moon's near side, taking into account geometric distortion around the limbs. In this way, they could rephotograph parts of the lunar far-side.

The rectified lunar atlas can now be seen at https://www.lpl.arizona.edu/si...

This was all done using telescopes, photographs, and optical projection ... all analog, earth-based work. (the main telescope was the 61" reflector at Mt. Bigelow in Tucson; the films were Kodak 3-AJ 10x10inch glass plates)

It was my honor to work with several of these astronomers, including Ewen Whitaker, Gerard Kuiper, Bill Hartmann, and Bob Strom. Brilliant scientists who would be astounded and impressed to see those NASA/Goddard videos. What we take for granted today, once required several years of detailed work.

Re:Science,much?

[osu-neko]

we can only see 50% of it's surface on any given night

So which nights can we see the other side? Oh, never.

Actually, on any night other than the one precisely a lunar month from the given night, you can see some of that other side (the 50% you can't see tonight). That's what libration does -- expose some of that other 50% that you can't see tonight. Not all of it, sure, but some. You can only see 50% on any given night, but you can see 59% over time. Thus, 18% of tonight's "other side" will be "this side" on some other night.