Bad Astronomy

Seeking legendary bad astronomy

So, what’s wrong with this picture?

Answer: Aaaaiiiiieeeee!

OK, first, a little background.

The crescent Moon can be a stunning sight. It hangs near the Sun after sunset (or before sunrise), up in the west (or east) while people are still out and about. The shape itself is lovely, and it shines a pearly white in the deepening blue sky… and sometimes you can see the “dark” part of the Moon as well, softly glowing with reflected Earthlight.

Yet for all its beauty, and its position both in time and in the sky making it obvious and well-observed, people still seem to massively screw up their understanding of it.

I give you the program “Legend of the Seeker”, the progenitor of that screen capture above, a fantasy series I had never even heard of until BABloggee Tom Elmer pointed it out to me. And why would he torture me so? So I can rail and froth about that picture depicted above, of course.

First, watch the scene yourself (note: that’s a link to Hulu, which I think is still only available inside the US; if that link takes you to the wrong episode it’s the 12th one of the first season). Don’t bother watching the whole thing (thank me later for that), but instead go to the 11 minute mark.

In this scene, Zedd, a wizard (you can tell from his hair) and the fair damsel Kahlan are schwitzing over an cursed boy. They have to break the spell, of course, but the sage says there is a deadline… they have to do it before the Moon covers three bright stars in the sky.

Of course! If I had a dollar for every time that’s happened to me, I could afford a stylish haircut like Zedd’s.

Anyway, take a look at the screen shot again. See the problem? Think on this: in the script, Zedd says, “Do you see how one star is beginning to disappear behind the Moon?” And you can clearly see that one of the three stars is very close to the edge of the lit crescent part of the Moon.

Got it now?

Here’s a basic astronomical fact: the Moon is a solid, opaque sphere. With me so far? Good. So when we see it as a crescent, it’s because we can only see a small part of the Moon that’s being lit by the Sun (we’re seeing that part from a shallow angle), and not because the Moon is physically like a slice of watermelon with a bite taken out of it.

So when the Moon is a crescent, the dark part is just unlit Moon, and not a scoop taken out of it. The only way to see stars superposed on the dark part of the Moon would be for the stars to be between the Moon and the Earth!

Now, the Sun – which is a star, you may recall – is 1.4 million kilometers across, and the Moon is only 400,000 km away, so you may see the problem here. Given that the Moon is the closest astronomical object in the sky, and the nearest star besides the Sun is 100 million times farther away, you might understand that any star we see would be behind the Moon, not in front of it.

So there’s no way to get stars between us and the Moon so that we see them against the dark part of the Moon. Of course, “Legend” is fantasy, so maybe in that universe stars are really really dinky. And close. And tied to mysterious curses.

But there’s a bigger mystery here: why does the fair damsel Kahlan look so much like Jessica Stover, who is also making a fantasy movie, and who also once asked me about phases of the Moon – which is in fact how we met?!