Full, and low on the horizon? Like on greeting cards, etc.?

From the full article as it appears on Reuters:
"One of the scientists who discovered the satellites couldn't resist making some spooky allusions with the announcement."
I think he's just making a (lame) joke because of announcing the moons on Halloween.

well, that was my thought, too, Myr, but the quote above seems to read otherwise. of course, they might have been mis-quoted...

>we're describing these Halloween moons

i.e., moons discovered (or at least announced) on Halloween.
-ron (moaning) o.

I would have said "we're describing these as Halloween moons".

then it would have made sense to me.