Saturday, February 26, 2011

Solar Eclipse

There are four types of solar eclipses: total, annular, hybrid, and partial. The occurrence of each solar eclipse as per observer will depend on three main factors: the position of the Earth and Moon along their orbital paths (i.e., whether near its apogee, near its perigee, or somewhere in between), the location of the observer on Earth, and the alignment between the Earth, Sun, and Moon.

In this article, we'll focus on the effect of the positions of the Earth and Moon along their orbital paths. Their positions will determine whether the eclipse witnessed by an observer on Earth will be total, annular, or hybrid.

Recall that the Earth's and Moon's orbits are elliptical in shape. That means, in some instances, the Earth can be at its farthest position from the Sun (known as its apogee), while in others, it can be at its nearest (perigee). In still other instances (in fact, more frequent than the other two), the Earth can be located somewhere in between the two extremes.

When the Earth is at its farthest, the Sun will naturally appear smallest to an observer than if the Earth were at its nearest. Hence, all things considered equal, the Moon will be able to cover a greater part of the Sun when the Earth is at this position.

Now, since the Moon's orbital path about the Earth is also elliptical, there should be a position wherein the Moon will appear largest – its perigee. The nearer the Moon, the bigger it will appear from an observer on Earth, and the bigger its obstruction (if ever) of the Sun. As we can see, the positions of the Earth and Moon along their orbital paths are crucial in producing the type of solar eclipse.

So, at which extreme positions of the Earth and Moon can we have the smallest Sun and largest Moon?

The Sun is smallest when the Earth is at its apogee while the Moon is largest when the Moon is at its perigee. Thus, if these two scenarios happen at the same time while the Earth, Sun, and Moon are fully aligned, many of us will experience the most total solar eclipse there can ever be.

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