Jim Turner, Age 7, Of Cochran, A1berta, Canada, for his question:

What is meant by the transit of Venus?

We use the word transit in everyday talk. When we say that a friend is in transit between Calgary and Seattle, we mean that he is traveling between Calgary and Seattle. But astronomers have a different meaning for this word transit. A transit happens when a heavenly object crosses a certain point in the sky.
On a clear night, the velvety sky is spattered with sparkling stars. Very often you can find one bright dot that does not wink and blink like its twinkling neighbors. It shines with a steady light. This steady eye in the sky is not a star, but a planet. It could be the planet Venus, but you will not see a transit of Venus until June 7, 2004. That date is exactly 39 years and 11 months from today.
When the transit happens, Venus passes slowly across the dazzling face of the sun. We are used to seeing Venus in the night sky. Sometimes it is the morning star that rises in the east just before the sun. Sometimes it is the evening star that follows the sun to bed as it sets in the western sky.
There are times when we cannot see Venus in the sky at all. At other times the golden planet is 15 times brighter than Sirius, the dog star, which is the brightest of all the true stars in the heavens. If you watch Venus through a telescope night after night you see that it has phases like the moon. Its shape seems to change from a thin curve to a half circle, then to a full circle, back again to half phase and then to quarter phase again. Then it disappears for a while.
These things happen because Venus and the earth are circling around the sun on different orbits. The earth is farther from the sun, and we take much longer to make each round trip around. Venus often catches up and passes us. It passes between the Earth and the sun, but as a rule it crosses above or below the sun. Once in a great while it passes exactly between us and our view of the sun and we get a transit of Venus.
We cannot watch this directly because it is dangerous to look directly at the sun. But when a transit of Venus happens, telescopes around the world are ready to record it. They show Venus as a small dark dot inching its way across the dazzling face of the sun. A transit of Venus has happened only five times in the last 300 years.
Venus passes between us and the sun once in every 584 days. But the orbits of the two planets are tipped at different angles, and as a rule it crosses above or below the sun. A transit across the face of the sun is very rare. It happened in 1874 and eight years later in 1882. The next transit of Venus will be in 2004, and eight years later there will be another one.