How embarrassing is it for someone with advanced degrees in science and a life long love of space exploration to be caught referencing the famed "dark side of the moon" (at least I was up on my Pink Floyd) only to be met by a surprised look from my astronomical colleague with the comment, "Loretta, you know there isn't really a dark side of the moon."
But how can it not exist? There is a whole ALBUM dedicated to it. Well it's true. Although there is a part of the moon that we never see from Earth (since it always keeps the same side towards us), the backside isn't dark. It's just the "far side of the moon" (first seen by human eyes in 1968 during Apollo 8). Half the time the far side is in sunlight and half the time it's not, just like the Earth. Ok, ok I get it.
Recently, JAXA, the Japanese Space Exploration Agency, released high-res pictures of the "earthrise" as seen from it's new lunar orbiter, Kaguya. The pictures are a hi-def update of the original "earthrise" picture taken during Apollo. The problem? It's a misnomer. From your lunar base, you will never see an earthrise...
Why?
Remember the moon always keeps one face towards us, so conversely if you were at an outpost on that face you would consistently see the earth at the same place in the sky every day all of the time (the Earth would rotate in front of you and even go through phases like the moon does but that's about it).
So why all the earthrise pictures? Earthrise then is only seen from the perspective of a spacecraft coming around from the back side of the moon back into view of the earth again. As the spaceship orbits from the far side of the moon to the near side of the moon, earth will gradually come into view from behind the limb (edge) of the moonscape, producing an artificial "earthrise."
JAXA was actually nice enough to point this out in their press release and even went so far as to include a graphic showing the position of the satellite as it took the "earthrise" and "earthset" images to help people visualize it.
I re-posted the new JAXA earthrise, the original earthrise and the explanatory graphic below.
The other key fact about the moon? The lunar day is 14 earth days long and lunar night is 14 earth days long. All Apollo missions landed during the lunar 'day' and none stuck around long enough to see a lunar night. (It gets pretty cold at night...)
Image: Dark Side of the Moon Album Cover Art- Cool Flickr user, HD Earthrise- JAXA, original earthrise- NASA, graphic- JAXA.
