Lunar madness

[kengr]

Reading a book I'm wanting to shake the author.

He's making *horrid* mistakes about lunar phases.

First instance was mentioning a full moon about "a third of the way to the zenith". Ok, no prob. Except it's late afternoon.

Not possible. Not even on an alien planet.

Another scene some weeks later has a half full moon near the horizon at dawn. Also not possible.

Y'see, the phase of the moon is determined by the angle between the moon and the sun.

At full, they are 180 degrees apart. So the moon is rising as the sun sets.

At half, they are 90 degrees apart. And so on.

Comments

[brockulfsen.livejournal.com]

It is possible on an alien planet, if it has two suns.

[kengr]

Only a single sun. And besides, then you'd get different phases *at the same time* for the two suns.

[mikkop.livejournal.com]

Well, yes, that's annoying.

I've mostly read those children's books lately, and it seems that the authors think that they can break every rule if they have talking animals...

[fayanora.livejournal.com]

I don't get it. I've seen the full moon out during the daytime.

[kengr]

Nope. You may have seen a *gibbous* moon. And if you did, it was closer to sunrise or sunset than to noon.

[fayanora.livejournal.com]

It was in the afternoon, about 2 PM.

[kengr]

Ok, that makes the sun about 60 degrees above the horizon. Since it didn't look like a half moon, it had to be more than 90 degrees from the sun.

So my guess is that it was no more than 30 degrees above the *eastern* horizon.