Pink Floyd Got It Right

China proposes, according to CNN, to land a probe on the “‘dark side'” of the moon. Yes, if you think I nested the quotation marks there, you’re right. No less than three times in their story do CNN refer to some part of the moon with those two words, always in quotation marks. That might be fine, if anyone were being quoted. But no source is given for that phrase, and no explanation of what it means is really offered either. From the text, one can infer that what the Chinese are planning to do is land a probe on the far side of the moon, the “back” half that we can’t see from Earth (actually, owing to the inclination of the moon’s orbit, and the fact that it sort of rocks this way and that, we can see rather more than half of it from Earth, but you get what I mean, I’m sure).

Astronomers have long found this enduring misnomer to be painful, as it ought easily to be the case that everyone can see (literally see) that the side facing the Earth changes from being wholly illuminated, to partially illuminated, to unilluminated (well, except for the faint glow of reflected Earthlight, which is pretty cool, when you look at it), back to partially illuminated, and repeat. What this means is that, in a way, there is a dark side to the moon, but it’s not the side that faces away from the Earth: it’s the side that faces away from the Sun. While the moon keeps one face towards Earth all the time, it shows its entire globe to the Sun, once every complete lunar orbit (it really takes a little longer than that, because the Earth-moon system also orbits the Sun, which I can make plain on the back of a paper napkin at the bar in Clyde’s, but not on this blog). This means that while, yes, there is a dark side to the moon, that side is constantly changing. Which is not true of the far side, which is the side the Chinese plan to explore.

No, that wasn’t important, but it irks astronomers and I once wanted to be an astronomer, so, on their behalf, I have groused about it here.

(Of course, there is still another view on this, starting at 1:35, here.)