Jim Phillips wrote:

> 43. In Gulliver's Travels Jonathan Swift described the two moons of Mars,
> Phobos and Deimos, giving their exact size and speeds of rotation. He did
> this more than 100 years before either moon was discovered.

At least according to Kim Stanley Robinson (Green Mars) this was a lucky
guess...  The reasoning went as follows:

- Venus has 0 moons, Earth has 1, Jupiter has 4, so Mars probably has 2.
- We can't see them, so they are probably small and close to the surface
of the planet.
- If they are close to the surface, then they must be fast.

Quite well reasoned, but at the same time, a lucky guess.

Damian.