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What is a Total Solar Eclipse?

Mar 07, 2017 12:01PM ● Published by Tracy McCoy

Gallery: Solar Eclipse [2 Images] Click any image to expand.

What is a total solar eclipse and why is it so special? Simply put, a total solar eclipse is when the shadow of the Moon passes over part of the Earth’s surface. The photo above shows this shadow as seen from the International Space Station. A total eclipse is by far the most spectacular kind of eclipse and only can occur when the Moon is perfectly aligned between the Sun and the Earth and the Moon is passing close enough to the Earth so that the Moon’s dark shadow reaches the surface of the Earth. Below is a simplified diagram, not to scale, of a total eclipse:

Because the orbit of the Earth around the Sun and the orbit of the Moon around the Earth are not perfect circles and because the Moon’s orbit is about 5% skewed when compared to the Earth’s orbit around the Sun, the alignment required for a total solar eclipse is a rare event. Such an eclipse will occur at a particular location only about once every 350 – 400 years. This means that for most people, the eclipse next August 21st will be a once in a lifetime chance to see one of the most stunning phenomena in nature.

The shadow of the total eclipse will travel across the United States from Oregon to South Carolina in about 1 hour and 45 minutes, moving at about 1200 mph. Since the eclipse shadow is only about 60 miles in diameter, the duration of the time when the Sun will be completely covered at any location is brief. In Dillard, Georgia, which will be on the centerline of the shadow, the duration of darkness will be 2 minutes, 38 seconds – only 2 seconds less than the longest duration anywhere in the United States. Further north or south of the centerline, the duration will be increasingly shorter until locations greater than 30 miles from the centerline will have no total eclipse at all.

Locations in North America beyond the 60 mile wide path of totality will experience a partial eclipse. For example, Atlanta will have a 97% partial eclipse. That sounds impressive, but people there will experience none of the special effects of a total eclipse. Since the Sun is so incredibly bright, they will just notice a slight decrease in Sunlight intensity. Even those wearing eye protection lenses will only see the Sun narrowing to a bright crescent, but no blackout of the Sun. This is why it is well worthwhile to travel to the path of totality and to be as close to the centerline as possible. A bonus of being in the path of a total eclipse is that you will also be able to observe a partial eclipse for about one hour before and after totality, as the Moon slowly covers more and more, and then less and less, of the Sun.

An ideal place to experience the August 21st total eclipse will be the OutASight Eclipse Festival on the campus of Rabun Gap-Nacoochee School, which will feature special presentations and activities throughout the day and during the eclipse itself. See “explorerabun.com/total eclipse” for full details.

Hope to see you there!

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