Doug Hammer, age 9, of Marshall, Oklahoma, for his question:

Could Venus eclipse the sun?

We see a solar eclipse when the moon passes exactly between us and the sun. The planet Venus is closer to the sun than we are. So it seems logical that it too could cause an eclipse. In a way, this does happen. But Venus does not blot out the whole sun, as the moon does during a solar eclipse. This is because faraway things appear smaller. And Venus is 60 times farther away from us than the moon. Although the sun is 400 times wider than the moon, the moon can cover its entire face because the sun is 400 times farther away.

The sun is only three times farther away than Venus. When Venus passes between us, it appears as a small black dot on the huge face of the dazzling sun. Astronomers have a special name for this kind of eclipse. They call it a transit. And they can predict the transits of Venus, just as they predict the solar eclipses. There may be one or two transits of Venus in a year    then no more for another eight years.