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Solar Eclipse 101 by NASA: Who? What? Where? When? and How?

August 13, 2017 by Paul Shepard

One week from today, on Monday, August 21, 2017, all of North America will be treated to an eclipse of the sun. Anyone within the path of totality can see one of nature's most awe-inspiring sights - a total solar eclipse.

This path, where the moon will completely cover the sun and the sun's tenuous atmosphere - the corona - can be seen, will stretch from Lincoln Beach, Oregon to Charleston, South Carolina. Observers outside this path will still see a partial solar eclipse where the moon covers part of the sun's disk.

California’s San Juaquin and Coachella valleys, both key solar producing regions, will see coverage of around 76% and 62%, respectively. And, although it will be spared the full impact, California is planning for the potential of major disruptions in its grid as the production of electricity from photovoltaic installations falls from a normal level of over 8,700MW to 5,600MW while demand is rising by 1,300MW primarily due to the increased use of electric lights.

California unveiled CalEclipse.org with a call to Californians to Do Your Thing and reduce electricity use during The Great Solar Eclipse on August 21, 2017.

The following information is from the "Eclipse 101" overview page of the official NASA Total Eclipse website (the site also includes a list of solar eclipse-related apps):

Everyone in the contiguous United States, in fact, everyone in North America plus parts of South America, Africa, and Europe will see at least a partial solar eclipse, while the thin path of totality will pass through portions of 14 states.

Image Credit: NASA's Scientific Visualization Studio. This map shows the globe view of the path of totality for the August 21, 2017 total solar eclipse. You can find more information online

This celestial event is a solar eclipse in which the moon passes between the sun and Earth and blocks all or part of the sun for up to about three hours, from beginning to end, as viewed from a given location.

Diagram showing the Earth-sun-moon geometry of a total solar eclipse. Not to scale: If drawn to scale, the Moon would be 30 Earth diameters away. The sun would be 400 times that distance.

For this eclipse, the longest period when the moon completely blocks the sun from any given location along the path will be about two minutes and 40 seconds.  The last time the contiguous U.S. saw a total eclipse was in 1979.

You can see a partial eclipse, where the moon covers only a part of the sun, anywhere in North America. To see a total eclipse, where the moon fully covers the sun for a short few minutes, you must be in the path of totality.

Example of eclipse times for cities in the path of totality.

The path of totality is a relatively thin ribbon, around 70 miles wide, that will cross the U.S. from West to East.  The first point of contact will be at Lincoln Beach, Oregon at 9:05 a.m. PDT. Totality begins there at 10:16 a.m. PDT.

Over the next hour and a half, it will cross through Oregon, Idaho, Wyoming, Montana, Nebraska, Iowa, Kansas, Missouri, Illinois, Kentucky, Tennessee, Georgia, and North and South Carolina.  The total eclipse will end near Charleston, South Carolina at 2:48 p.m. EDT.  From there the lunar shadow leaves the United States at 4:09 EDT.

Its longest duration will be near Carbondale, Illinois, where the sun will be completely covered for two minutes and 40 seconds.

Times for partial and total phases of the eclipse vary depending on your location. This interactive eclipse map will show you times for the partial and total eclipse anywhere in the world.

You never want to look directly at the sun without appropriate protection except during totality.  That could severely hurt your eyes.

Check with local science museums, schools and astronomy clubs for eclipse glasses—or purchase an ISO 12312-2 compliant pair of these special shades!

This list describes when to wear your glasses and when you can safely look at the eclipse, only during totality!

There are many ways to safely view an eclipse of the sun including direct viewing - which requires some type of filtering device and indirect viewing where you project an image of the sun onto a screen. Both methods should produce clear images of the partial phase of an eclipse.  Click here for eclipse viewing techniques and safety.

Using a projection method to view the sun.