Total solar eclipses are spectacular to witness, interesting to predict, and facilitate some very interesting
experiments, but the root cause of them is quite simple: a shadow. The very word eclipse means “to block.” In the
case of a solar eclipse, the Moon is blocking the Sun from our view. Thus, the shadow of the Moon falls over the
Earth (and, in case you were wondering, during a lunar eclipse, the Earth blocks the Sun from the Moon so that the
shadow of the Earth falls over the Moon).
There are three conditions that must be met for a total solar eclipse to happen:
1) the Moon must be in its New phase
2) the Moon must be at a node in its orbit
3) the Moon must be at perigee in its orbit
The Moon is in its New phase once every month, placing it in a general position between Earth and Sun. However,
the Moon's orbit is tilted with respect to a line drawn connecting the Earth and Sun, so it is possible for the
Moon to be New, yet not on the direct line between the Earth and Sun. When it is, we say it is at a node. Lastly,
the Moon can only cover up the Sun completely if the Moon appears exactly as large in the sky as the Sun does.
Since the Moon's orbit is not a perfect circle, it is sometimes closer to us (perigee) than it is at other times
(apogee).
To find out more about eclipses and to see some really great demonstrations, book the Moonshadow Team to give a
presentation!