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Solar and Lunar Eclipses The fact that the Moon always keeps the same face turned toward the Earth is not a coincidence. What is a coincidence is the fact that the Sun and Moon appear almost the same size in our sky. This coincidence of nature produces the phenomenon of solar eclipses, which are among the most spectacular astronomical events one can witness. The moon also experiences lunar eclipses, which you can think of as solar eclipses seen from the Moon.

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Lunar Eclipses

Lunar eclipses occur whenever the Moon passes into the shadow of the Earth. The shadow of the Earth can be divided into two parts, the umbra and the penumbra. In the umbra, the Sun is totally blocked by the Earth. In the penumbra, the Sun is only partially blocked. Therefore, if the Moon is completely inside the umbra, there will be total lunar eclipse. If only part of the Moon passes inside the umbra, there will only be a partial lunar eclipse. If the Moon only passes through the penumbra, we say that there is a penumbral lunar eclipse. If you were on the Moon at that time, you would see a partial solar eclipse. A lunar eclipse. For a lunar eclipses to occur, the Moon must be “behind” the Earth as seen from the Sun. If so, then why we do not have a lunar eclipse every month? The reason is that the plane of the Moon’s orbit does not coincide with the plane of the Earth’s orbit. So, during most full moons, the Moon is either south or north of the orbital plane of the Earth. For the same reason, we do not see a solar eclipse during every new moon. Why we don’t see an eclipse every month. Solar Eclipses If you reverse the roles of the Earth and Moon in the above paragraphs, you will get a solar eclipse instead of a lunar eclipses. The most common kind of solar eclipse is the partial solar eclipse. If you are at the right position at the right time, you might see a total solar eclipse. However, because the path of a total eclipse is very narrow, you will probably not see even one total solar eclipse in your lifetime if you stay in one place on the Earth and wait. A total solar eclipse. A total solar eclipse is a very stunning experience, and people will travel around the globe to watch it. During a total eclipse, the sky is dark enough to see bright stars and planets. The main disk of the Sun is blocked by the Moon. The Sun’s much dimmer corona becomes visible. A total eclipse typically lasts about two minutes. Then, you see the Sun again, and the total eclipse is over. There is another kind of solar eclipse. Since the distance between the Moon and the Earth is not constant, the angular size of the Moon can have a small variation. It could happen that the Moon is at the right position, but its angular size is too small, to cover the whole Sun. This is called an annular eclipse. Viewers in the path of an annular eclipse will see a ring of Sun at mid-eclipse. An annular solar eclipse. Because of their tidal interactions, the Moon is slowly receding from the Earth. Millions of years from now, there will be no more total solar eclipses, because the Moon will be too far away to cover the Sun in the Earth’s sky.