Good and bad explanations

Joe Carter went over to Meyerz's comments and asks for a materialistic explanation of the mind. This raises a question I've had spent a fair amount of time thinking about, but have never tried to work up a systematic answer to.

Let's look at UFOs. It seems intuitively right to me that assuming any mysterious light in the sky is an extraterrestrial craft is a bad explanation for the event, while if you hear a pilot say he was flying a craft with the described lights in the given place and time, you've got a good explanation. Why exactly is this?

Well, the first answer is there's evidence for the second case, but in the first case, the mere existence of the light may be seen as evidence. Just throwing out the word "falsifiablism" doesn't quite do it; it's on the right track, but one could claim the potential falsifier for the alien theory is a lack of unexplained lights.

There's a very distinct problem with the alien idea, though: it's just one of an infinite number of possibilities. Suppose a light cannot really cannot be explained by any known phenomenon. The light still might not be an alien spacecraft, it might be the vessel of a secret civilization living inside the Earth (something actually proposed by some UFO buffs). This objection would hold true even if no one was imaginative enough to come up with the civilization in the Earth.

The source of the problem is aliens are one of an infinite number of things that can be used to explain any mysterious light, regardless of its characteristics. A good explanation refers to specific characteristics of the thing, and would be unable to explain the thing if the characteristics are otherwise. The pilot explanation requires that observations of the lights match up with what is know about the plane, what it was doing, and human perception (because optical illusions might make a routine maneuver seem extraordinary).

If this line of reasoning is correct, to say "gravity explains the motion of the planets" is a horrible argument for the theory of gravity; the correct argument is "gravity explains planets moving in the exact way we observe them moving, and would not explain lots of different movements of planets." Similarly, postulating God to explain every mystery in the universe is faulty, and we are better off admitting we can't explain something than invoke such an explanation.