Full Solar Eclipse:
These are a happy accident of nature. The sun’s 864,000-mile diameter is fully 400 times greater than that of our puny moon, which measures just about 2,160 miles. But the moon also happens to be about 400 times closer to Earth than the sun (the ratio varies as both orbits are elliptical), and as a result, when the orbital planes intersect and the distances align favorably, the new moon can appear to completely blot out the disk of the sun. On the average a total eclipse occurs somewhere on Earth about every 18 months.
There are actually two types of shadows: the umbra is that part of the shadow where all sunlight is blocked out. The umbra takes the shape of a dark, slender cone. It is surrounded by the penumbra, a lighter, funnel-shaped shadow from which sunlight is partially obscured.
During a total solar eclipse, the moon casts its umbra upon Earth’s surface; that shadow can sweep a third of the way around the planet in just a few hours. Those who are fortunate enough to be positioned in the direct path of the umbra will see the sun’s disk diminish into a crescent as the moon’s dark shadow rushes toward them across the landscape.
During the brief period of totality, when the sun is completely covered, the beautiful corona — the tenuous outer atmosphere of the sun — is revealed. Totality may last as long as 7 minutes 31 seconds, though most total eclipses are usually much shorter.
Some of the upcoming Solar Eclipses are:
Sept. 13, 2015: Partial eclipse. Time of greatest eclipse: 6:54 UT. Visible from southern Africa, south Indian Ocean and Antarctica.
March 9, 2016: Total eclipse. Time of greatest eclipse: 1:58 UT. Visible from Australia, Sumatra, Borneo.
Sept. 1, 2016: Annular eclipse. Time of greatest eclipse: 9:08 UT. Visible from Atlantic Ocean, central Africa, Madagasgar, Indian Ocean.