Q: How many craters are there on the Moon?
A: On the side of the Moon that is visible from the Earth are 30,000 visible craters. There are many more small craters there which we cannot see. They are smaller than 1/4 of a kilometre in diameter.

Q: How long is the tail of a comet?
A: There are some comets which have no tail as they passed near the Sun. As a rule, however, comets' tails are very, very long. The tail of Halley's comet was about 160 million kilometres long, longer than the distance between the Earth and the Sun. The Great comet of 1843 had a tail over 480 million kilometres in length.