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Solar Eclipse

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The ecliptic is the a virtual plane that splits the Sun in half. Along this plane orbits the 9 planets, their moons and the asteroids. Our Moon travels about this same plane so there are times when the Moon comes between the Earth (which leads to a solar eclipse) and other times when the Moon is "behind" the Earth (which leads to a lunar eclipse).

It is important to realize that this ecliptic is only an apparent plane as the orbits are inclinated by various degrees. In other words, the planet orbits are not required to rotate on this plane. Same is true for our Moon - in fact, our Moon's orbit has an inclination of 5. This inclination is important because this is the reason for having a variety of eclipse types - i.e. partial or total.

In addition to an inclination, all orbits also have a slight elongation. It is very rare, and safe to say impossible, for an orbit of a body about another body to be an perfect circle. According to Newton's Law, objects with mass will affect other objects with mass. As Earth orbits the Sun because of the gravity attraction by the Sun, Earth's mass also affects the Sun (although very little, but this can still be measured). The result is an elliptical orbit. This measured result is called eccentricity.

The figure above demonstrates the conditions required for and eclipse to occur. When the Earth, Moon and Sun lay on the same plane, this is called the Line of Nodes.

Because of the inclination and elongation of Moon's orbit about Earth, there are three variations of a Solar Eclipse.
For some nice animations of a Solar Eclipse, click on the images to the right and left.

The image on the right demonstrates a total eclipse. The image on the left shows how the shadow moves across Earth. The darker shadow will be the locations of a total eclipse while the lighter shadow will be the locations of the partial eclipse (videos care of Swinburne Astronomy Online).

If the umbra is focused to a point on the Earth's surface, a total solar eclipse will occur.

If the umbra is focused above the Earth's surface, an annular eclipse will occur.

If the Moon orbits just above or below the Line of Nodes, a partial solar eclipse occurs. Notice the absence of a defined Umbra.

For a list of Solar Eclipse dates, click here. For Lunar Eclipse information, click here. To go back to Our Sun, click here.

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