A total solar eclipse. Source: SoftPedia
There are two types of eclipses, lunar and solar, but I’d like to talk about the latter. Solar eclipses can be broken down into four subtypes: total, partial, annular and hybrid. In order for any of these to happen, the Sun, Moon and Earth must form a straight–or almost straight– line. A total eclipse is pictured above, and is when the Moon blocks the entire sun, though one could argue that this is actually an annular eclipse, where the Moon blocks most of the Sun but a ring, or annulus, of the Sun is still visible. Partial eclipses are when the Moon, partially, blocks the Sun and hybrid eclipses are combinations of 2 of these types, where the Moon partially and then either totally or annular-ly blocks the Sub.
These eclipses happen due to chance. The first is the huge coincidence that the Sun is about 400 times the size of the Moon, and is also about 400 times further than it, relative to Earth. Because of this, the Sun and Moon appear to be roughly the same size in the sky. The Moon also has to be at one of its nodes for this phenomenon to occur. The Moon’s nodes are where it crosses the ecliptic as it orbits the Earth, which makes sense, because the Moon has to be between the Sun and Earth to block the Sun’s light from reaching us here. Now, in order to have a total solar eclipse, the Moon must be at or very near the perigee of its orbit, which is where it is closest to Earth. If the Moon is not at or near the perigee, it appears slightly smaller in the sky and we would be left with an annular eclipse, as opposed to the total eclipse.
