Eclipses.

When the Sun, Moon and Earth come into a straight line an ECLIPSE occurs. This does not happen very often because the Moon's orbit is inclined to that of the Earth. A TOTAL eclipse occurs when all the Moon or Sun is blotted out. A PARTIAL eclipse is when only part of the Sun or Moon is covered.

Lunar eclipse

When the Earth comes between the Sun and the Moon we get a 'Lunar eclipse' or eclipse of the Moon (Figure 1).

The Moon passes into the shadow of the Earth, it ever completely disappears because a small amount of the Sun's light is refracted by the Earth's atmosphere and falls on the Moon during the eclipse. This light gives the Moon a reddish appearance.

You can see form Figure 1 that at the distance of the Moon the Earth's shadow is much bigger than the Moon and so the Moon takes some time to pass through it.

Solar eclipse

Its much more impressive when the Moon comes between the Sun and the Earth. The shadow of the Moon falls on part of the Earth and this is a Solar eclipse or eclipse of the Sun (Figure 2(a)). When seen from the Earth the Noon and Sun look almost exactly the same size and so in a total eclipse the Moon just covers the Sun.

Figure 2(b) shows the view of the Sun from the Earth during the eclipse. Diagram (c) shows the total eclipse. The shadow of the Moon falls on the Earth and because the Moon and Earth are moving compared with the Sun this shadow moves across the Earth's surface during an eclipse.