Yael: We're here on this chilly winter night gazing up at a luminous full moon. Beautiful, Don, don't you agree?

D: Yeah, I guess so.

Y: That's not your line. You're supposed to say, "Yes, Yael. It's like a pale, unblinking eye inviting us to ponder the majesty of the universe."D: I'm sorry, I'm just not feeling very inspired.

Y: What's the problem?

D: How come we've only got one moon, while other planets have a bunch? Jupiter alone has nearly forty moons! Even Mars has two. It's not fair.

Y: Maybe not, but what can you do? Astronomers think that our moon was created billions of years ago when something really large collided with Earth, knocking rocks and debris into orbit. The orbiting stuff eventually came together to form the moon. When it comes to larger planets like Jupiter, it's possible that when the planet was still young its atmosphere stretched out far into surrounding space. The gas could have trapped passing objects and drawn them into Jupiter's orbit, creating small, irregular moons.

D: That's interesting, but I'm still envious.

Y: Well, we might only have one moon, but it's a pretty good one, as moons go. First, it's a very large moon relative to the size of our planet. And it's close enough to have a significant effect on ocean tides and climate. Plus, our moon makes for some pretty spectacular nighttime sky gazing.

D: That's true. I guess our moon isn't that bad.

Y: Learn to love it, Don. It's the only one we've got.