Tonight is the 13th and final full moon of 2012. It is also an example of how a lunar month and a calendar month don’t exactly match up. The Moon orbits the Earth, returning to the same place in the sky once every 29.5 days, but our months have 28, 29, 30, or 31 days in them. Therefore some years have twelve full moons, and other have thirteen. And speaking of thirteen, this video illustrates every full moon of 2013. Quite hypnotically, I might add.
The central image shows the phase of the Moon at any given moment, while the clock runs forward in seconds, minutes, hours, days, and months in the lower right. The upper left locates the Moon in its orbit around the Earth, with the Sun in a fixed direction. The wobble you see as the phases of the Moon change is the result of the inclination of the Moon’s axis with respect to its orbit around the Earth. It’s no different from how the tilt of Earth’s axis with respect to its orbit around the Sun is responsible for our seasons.
In my opinion, the coolest part of this video is the line across the middle of the screen. The number line on the right side (28 - 32) indicates the ellipticity of the Moon’s orbit in units of Earth’s diameter (i.e., 28 = 28 x 12,756.2 km). The Moon’s distance from Earth oscillates between 28-32 Earth diameters (or roughly 360,000 km - 408,000 km). This variation is what allows for everyone’s favorite lunar phenomena: the Supermoon. A Supermoon is the coincidence of a full moon when the Moon is closest to Earth in its orbit. Watch the video closely and you can see the Moon growing and shrinking in size as it moves towards and away from Earth. Pretty cool, huh?
You can download your own copy and check up on the current Moon stats here.
Geek you in 2013! @Summer_Ash