LOUISVILLE, Ky. (WDRB) - Grab those glasses, sit back and get ready to see the total solar eclipse.

It's something many will only experience once in a lifetime. And WDRB meteorologist Jeremy Kappell says the Great American Eclipse on August 21, 2017 is very rare. 

By definition an eclipse is the obscuring of light from one celestial body by the passage of another.  To demonstrate this, all you really need is a source of light.  And two objects with one casting a shadow on the other. 

In a galaxy filled with stars, planets and moons, shadows are constantly being cast. But only here on planet earth, as far as we know, do they actually get noticed. In our solar system, that source of light, of course, is the Sun while the Moon and Earth play a game of "cast and catch."

A solar eclipse occurs anytime the moon crosses in a line directly between the sun and the earth. This typically happens about every six months somewhere on our planet. However, not all eclipses are created equal.

The most common is known as a "partial eclipse" where the shadow of the moon doesn't fall directly on the earth and the moon only covers up a portion of the sun. This last occurred here on April 8, 2005 and was not very noticeable with only about 20% of the sun covered.

Despite the fact the sun is MUCH larger than the moon, because it's also MUCH further away, it usually appears about the same size in our sky.  

However, due to the elliptical shape of the lunar orbit, the distance between the earth and the moon is not constant, and this affects what we see during an eclipse.

Unlike a partial, during an "annular eclipse", the shadow of the moon does fall directly on the earth. But because it occurs when the moon is further away, it doesn't fully block the sun creating the dramatic "ring of fire" effect last seen in our region on May 10, 1994.

The rarest eclipse of them all is the "total solar eclipse."  As opposed to the annular, in the total eclipse, the moon is close enough to the earth to fully cover the sun creating a moment of "totality" for the lucky few in its path. 

During totality, the sky becomes dark, the temperature drops and stars may even become visible! As a whole only one-tenth of one-percent of the Earth will experience totality during this eclipse, which is what makes this event so special.

For some folks, a lifetime will go by without seeing an event like this.  The last total solar eclipse to visit the state of Kentucky occurred some 148 years ago. Fortunately for those that are still here, the next one is only 7 years away.

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