This is pretty neat — it’s a visualization of the Moon’s phases and libration all throughout 2014, made by NASA’s Goddard Space Flight Center Visualization Studio. They’ve done these several times in the past, and this is the latest one.
For accuracy you just can’t beat it: the global terrain map you see in the rendering was made with actual images and measurements of the lunar surface obtained by the Lunar Reconnaissance Orbiter’s LROC camera and laser altimeter. It’s the most detailed imaging of the Moon’s surface available!
So you know about the phases, but why is the Moon rocking back and forth like that? That’s the libration effect I mentioned — read more below:
According to the GSFC description:
The Moon always keeps the same face to us, but not exactly the same face. Because of the tilt and shape of its orbit, we see the Moon from slightly different angles over the course of a month. When a month is compressed into 24 seconds, as it is in this animation, our changing view of the Moon makes it look like it’s wobbling. This wobble is called libration.
The word comes from the Latin for “balance scale” (as does the name of the zodiac constellation Libra) and refers to the way such a scale tips up and down on alternating sides. The sub-Earth point gives the amount of libration in longitude and latitude. The sub-Earth point is also the apparent center of the Moon’s disk and the location on the Moon where the Earth is directly overhead.
And there’s other motions of the Moon too:
The Moon is subject to other motions as well. It appears to roll back and forth around the sub-Earth point. The roll angle is given by the position angle of the axis, which is the angle of the Moon’s north pole relative to celestial north. The Moon also approaches and recedes from us, appearing to grow and shrink. The two extremes, called perigee (near) and apogee (far), differ by more than 10%.
Very cool! See this and other lunar visualizations on the GSFC “Dial-A-Moon” page here.
Note: this visualization does not include eclipses and/or bad viewing conditions. If it’s cloudy on August 9 don’t blame NASA. 😉