solar eclipse
The countdown to a rare celestial spectacle is on. On August 21st, people within the "path of totality," a 70-mile wide swath of land stretching from Oregon to South Carolina (14 states in all), will witness a total solar eclipse. The shadow of the moon will start in the Pacific ocean and travel at Mach 1.5 speeds across the continental U.S., creating an ethereal light show that eclipse hunters swear is unlike any other naturally occurring phenomenon. Eclipse enthusiasts describe the experience as transcendent, even life-changing.

Here are five things to know about the upcoming phenomenon:

1. A total solar eclipse is the result of a remarkable cosmic coincidence.

The incredible serendipity of a total solar eclipse on Earth is difficult to fathom. For the brief few minutes of a totality, the Sun and the Moon occupy the exact same space in our sky, perfectly overlapping one another. How is this possible? While the sun's diameter is 400 times the size of the moon's, the moon is 400 times closer to us. The phenomenon is unlikely to exist for any of the other planets in our solar system and may be fairly unique to the Earth. While other stars and planets assuredly have their own distinct celestial marvels, a total solar eclipse is one of our cosmic home's special treasures.

2. The eclipse offers a rare glimpse of the sun's secret majesty.

The light show that occurs during a total solar eclipse is unlike any other natural phenomena, which is why scientists flock to and study the event in droves. With a clear sky, a total solar eclipse affords spectators a rare, unfiltered glimpse of the sun's outermost layer, a million-degree halo of plasma that flairs and contorts under the powerful grasp of the magnetosphere. For a few precious minutes, our star reveals its ethereal beauty, including "Baily's Beads," prominences, coronal streamers and, if you're lucky, coronal ejections. Baily's Beads create a diamond ring effect that has inspired many paramours to propose marriage during totality (an act that an eclipse enthusiast might have found annoying).

Those not in the path of totality can still study rare shadows cast off of Earth-bound objects, including trees that cast off crescent shapes in the twilight.


3. The event, known colloquially as a syzygy, requires the observer to complete the phenomena.

An alignment of 3 or more celestial bodies is known as a syzygy. In this case, the total solar eclipse includes the sun, the moon, and the human observer. Not all of the Earth will rest in the path of totality, so the completion of the triage requires an intentional act

4. The last time there was a total solar eclipse visible only in the United States was in 1776.

The August 21st eclipse is especially rare because it is the first continent-wide eclipse to be viewable only in the United States since the same year the country came into existence. Additionally, it's the first time since 1918 that an eclipse's path of totality stretched unbroken from one coast to the other.

5. In 600 million years, total solar eclipses will no longer occur.

Because tidal friction gradually changes the Moon's proximity to us, total solar eclipses weren't always visible from the Earth and, in the distant future, perfect alignment of our sun and moon will no longer take place.

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NASA estimates that around 300 million people will experience the eclipse first-hand, though not everyone will be in the path of totality. The sun's light is so powerful that even those experiencing a 99.9% partial eclipse will not get the full effect.

Eclipses are profound cosmic events that have mesmerized humans throughout history. As early as 1050 B.C., Chinese astronomers recorded them using "oracle bones." In 1918, Sir Arthur Eddington Einstein studied a total solar eclipse to prove part of Einstein's general theory of relativity by displaying how gravity bends light.

If you're near the path of totality, you have a rare opportunity to gaze upon what eluded Canadian astronomer and eclipse chaser J.W. Campbell, who spent 50 years trying to experience a total solar eclipse only to see overcast skies 12 different times. For more information on the best spots to view the eclipse on August 21st, this site breaks down the path of totality.