About Solar Eclipses

A General Introduction to Eclipses and Eclipse Terminology

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Total EclipseA Solar Eclipse occurs when the moon gets in the way of the sun as seen from the Earth. It is a special event to see and only visible along a narrow path.

A Solar Eclipse can only happen during the lunar phase known as the New Moon. At the same time the Moon must be crossing the ecliptic. The Moon's Orbit is inclined by about five degrees relative to the ecliptic thus not every New Moon results in a solar eclipse and not every Solar Eclipse is a Total Solar Eclipse.

There is an amazing cosmic coincidence that the Moon is about 400 times closer to the Earth than the Sun. At the same time, the Sun is about 400 times larger than the Moon. What this means is that the angular size of the Sun and Moon as seen from the surface of the Earth is about the same in the sky. When viewed from the surface of Earth, both the moon and sun appear to be about one half degree in angular size – that is, about the size of your thumbnail when you extend your arm.

Because the size of the Moon and Sun in the sky is just about the same, there are times when you might see a Total Solar Eclipse and other times an Annular Solar Eclipse if you are in the right location - the central path of totality or annularity. If you are outside this path you might see a partial eclipse or no eclipse at all.

In astronomical terms, the Sun and Moon have roughly the same angular size. This makes it possible for a solar eclipse to occur. No other planets in our solar system enjoys the same one-to-one ratio between the size of a moon and the Sun.

The result is a very small shadow cast from the Moon onto the Earth. The shadow is in the shape of a cone. When it intersects with the planet Earth it is an oval shape about 100 miles across with a varying major axis size. There are two parts of the shadow, the umbra, the darkest part, and the penumbra, the surrounding ring that is not quite as dark. To see a total solar eclipse you must be inside the umbra. A partial eclipse is seen when you are in the penumbra.

During a Total Solar Eclipse you can see parts of the sun not normally visible to the eye such as the corona and prominences. These items are only visible during the short time between second contact and third contact of a Total Solar Eclipse.

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