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An eclipse is said to occur when one celestial body obstructs the view of another body relative to an observer. Normally it involves three celestial bodies although it could include more than that. One body is the source of light while the other acts as the obstruction. The third body is the point of observation of the phenomenon.
In the general description above, if you use the sun, moon and the earth then we get the conditions required for an eclipse to occur. Since the sun emits light which falls on the earth, if the moon comes in between the sun and the earth in a manner that they all fall in a straight line, then a solar eclipse occurs. See figure 1 below to get an idea of the concept explained here. The letters S, M and E represent the sun, moon and the earth respectively in the sketch.
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What is an Annular Eclipse?
Solar eclipses can be of various types such as partial, total, hybrid and annular eclipse. In this article we will learn mainly about the annular solar eclipse for such an eclipse is next due March 8, 2016 followed by another on August 21, 2017. The word, annular, means ring-shaped and when you see an annular eclipse picture in figure 2, you will come to know why it is named so.
As you can see in the picture, the sun looks like a ring of light surrounding the moon during this period. The explanation of this phenomenon is given in the subsequent section.
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How it occurs?
So let us find out how this phenomenon occurs. To understand this fully you need to comprehend the manner in which the Earth and Moon move relative to the Sun. The picture in figure 3 depicts the manner of revolution of the Earth around the Sun, and the Moon around the earth, the arrows giving the direction of motion. Just keep in mind that though the orbits shown are circular actually they are elliptical in nature. Now after seeing this picture you can imagine that if this were true, a solar eclipse should occur say every 24 hours when the Moon comes in between the Sun and the Earth, and a lunar eclipse should occur with same frequency, but we know that this does not happen. So is this picture wrong?
Well not really, but the only problem is that this picture shows (or we assume on seeing it) that this motion is coplanar or in the same plane but it is NOT so. The plane of the motion of the moon is different from the plane of motion of the Earth (remember the Sun is stationary as far as the solar system is concerned). The picture in figure 4 should make this clearer. You can see that it shows four positions of the Earth around the Sun and the relative position of the Moon when it is "New" and "Full". It clearly shows the angles and positions relative to each other and the positions in which eclipse should occur and when it cannot occur despite all three bodies in seemingly straight line.
So far as the general information about an eclipse goes, but how does an annular solar eclipse occur specifically? If you have not read my previous article about a penumbral lunar eclipse I suggest that you go through it by clicking here so that you can refresh you memory about the terms umbra and penumbra, as I will not be explaining them in detail again in this article.
An annular solar eclipse occurs when the Earth lies in the umbra region of the moon's shadow BUT the tip of the umbra does NOT touch the surface of the Earth. Because if the tip touches the surface of the Earth, then we will have a total solar eclipse and not an annular eclipse. You can think of a simple analogy that you are standing in front of a circular light bulb having a small circular disc of cardboard in your hand. Now think of the bulb as the Sun, the cardboard piece as the Moon and your eye as the Earth. If you place the disc at such a distance from the eyes that it fully covers the bulb, then it is equivalent to a total eclipse, while if you move it in such a manner that you just see a ring of the light bulb and the disc covers all but the outer periphery of the bulb, then it can be likened to an annular solar eclispe.
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The Annular Eclipse
The next annular solar eclipse is due on March 8, 2016 followed by another on August 21, 2017. However, each eclipse is not seen from every location on Earth. To know if you're going to be in the right place for either of the next eclipses in 2016 or 2017 follow the links. Also, do not forget to follow the safety instructions for viewing a solar eclipse. Click here to find out more about these precautions.
But if you cannot wait to see the eclipse just enjoy watching a few pictures (Figure 5) of annular solar eclipse so that you get an idea what you are about to view. To see an entire gallery of images related to annular solar eclipses just visit Gallery A or Gallery B pages.
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