What is a Solar Eclipse?

A solar eclipse occurs when the Moon is on a direct line between the Earth and the Sun, and the shadow of the Moon falls across a portion of the Earth. This will only happen during the New Moon phase, when the Moon is near the Sun in the sky, so only the back (unseen) side of the Moon is lit by the Sun.  

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Why doesn't an eclipse happen every month?

The Moon's orbit around the Earth is tilted about 5 degrees from the orbit of the Earth around the Sun (or the apparent orbit of the Sun around the Earth). Therefore, most of the time the Moon passes slightly below or above the Sun. Since an eclipse only occurs when the Moon and Sun are exactly lined up, that means there are possible "eclipse seasons" about every 6 months. The shadow of the Moon only creates a very narrow path along the Earth, and since the Earth rotates, this path will be along a different part of the Earth each time. 

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Why does the Moon appear to be the same size as the Sun?

We all know that the Sun is much, much larger than the Moon. But the Sun is also much, much farther away from the Earth than the Moon. In fact, the Sun is about 400 times the diameter of the Moon. But it also happens to be about 400 times farther away than the Moon. This cosmic coincidence means that they appear to be about the same size in the sky. Therefore, we have solar eclipses. In fact, we are the only planet in the solar system that has a Moon that is the correct size and distance to cause total solar eclipses. All the moons orbiting the other 5 planets are either too small or too big to cause eclipses. (Mercury and Venus have no moons.) They will either occult the Sun (completely cover it by a wide margin) or transit the Sun (appear as a tiny body crossing in front of it).

 

Does the Moon always appear to be the same size?

No, it does not. Because the Moon’s orbit is elliptical, not circular, the Moon is sometimes closer and sometimes more distant from the Earth. The most distant point, called Apogee, is 406,700 km (251,900 mi) away. The closest point, or Perigee, is 356,500 km (225,700 mi) away. This means that the Moon appears to be 14% larger near perigee than it is near apogee. A full Moon at perigee is also called a Super Moon. When the Moon is near apogee, it appears to be slightly smaller than the Sun (see below).

 

What are the 3 types of Solar Eclipses?

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• A Total Eclipse occurs when the Umbra, or dark central portion of the shadow of the Moon crosses over the part of the Earth that you are on. The Moon appears to entirely cover the Sun, except for the outermost solar atmospheric layer, called the Corona (or “crown”). The Corona can only be seen during a total solar eclipse. Totality lasts from a few seconds to a few minutes, depending on how close one is to the Center Line, where Totality lasts the longest.

 

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• An Annular Eclipse occurs when the Moon is near apogee, or the most distant point from the Earth, so the cone-shaped Umbra shadow does not reach the surface of the Earth. Beneath the Umbra is a part of the shadow called the Antumbra. When the antumbra crosses the portion of the Earth you are on, you will see an Annular Eclipse. The word annular is from Annulus, or Ring. The Moon appears to cover all the Sun except a narrow ring around the edge. So this type of eclipse is sometimes called a Ring of Fire. Annularity can last 2 or 3 minutes.

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• A Partial Eclipse occurs when the Penumbra, or outer lighter shadow of the Moon crosses over the part of the Earth you are on. It appears as though the Moon only covers part of the Sun. A partial eclipse can last up to 2 or 3 hours for the Moon’s penumbra shadow to traverse the face of the Sun. Both Total and Annular Eclipses have a partial phase that comes before and after the full eclipse. Again, the partial phases last 2 to 3 hours altogether.

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