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    On August 21, 2017, the moon will pass directly between the Earth and the Sun, blocking its light and causing a Total Solar Eclipse to occur over North America. The time the eclipse happens and extent of what type of eclipse occurs varies by location. Some will witness the total eclipse, while other parts of the US will only see a partial eclipse.

    The Total Eclipse will occur in a path about 70 miles wide which crosses all the way from coast to coast on the United States.

    This Eclipse is 100% certain to occur.
    Total Solar Eclipses happen somewhere on earth about every 18 months, but it has been over 40 years since there was a total eclipse over the continental United States.

    Those who are within the centermost path see the total phase (yellow below). Those who are not within that ~70 mile wide path will see an eclipse, but the moon won't block all of the sun's light.  That is called a Partial Eclipse.

    More Maps available from www.GreatAmericanEclipse.com

    100% of the continental United States, and much of Canada and Mexico will experience the eclipse in either a partial or total phase on August 21, 2017.

    The exact time that the moon blocks the sun is different for each exact location. An eclipse map or eclipse calculations are needed to pinpoint your exact timing circumstances. (Click here to see circumstances for your location) Exact contact times vary about every 100 feet and at different altitudes.

    Partial eclipses occur rather frequently.  Most people have seen a partial solar eclipse.  Very few people have seen a total solar eclipse. You have probably seen a PARTIAL eclipse at least once in your life.  You unless you travel internationally or were in the states listed below in February of 1979, YOU PROBABLY HAVE NOT SEEN A TOTAL SOLAR ECLIPSE.

      The last Total Solar Eclipse to touch the continental US happened February 26, 1979 and was only visible in Washington, Oregon, Idaho, Montana and parts of North Dakota.

      Because the moon blocks 100% of the light of the sun's surface, it will get dark during the daytime.

      The Sun has a faint, outer layer called the 'Corona' which can then be seen. This Corona is 1/1000 as bright as the sun's surface or 'photosphere'.  Its light is so dim, it isn't even as bright as just what light scatters in our atmosphere from the photosphere. Light from the photosphere has to be blocked from outside our atmosphere to see this phenomenon.

      We do not have total eclipses in every orbit of the moon because its orbit is tilted a little so it passes below or above the Sun most of the time.

      It is only safe to look at the Total Phase of an eclipse.
      Watching a partial eclipse without a solar filter can damage your eyes.

      Also, the moon's orbit is oval, so it moves closer and farther away in different parts of the orbit.  If the eclipse happens when the moon is too far away, then it's apparent size is a little smaller than the sun and it can't block the whole sun.  That's called an Annular Eclipse.   

      During an Annular eclipse, the surface (photosphere) of the sun is still visible and is still too bright to see the phenomenon seen during the total phase.

      There was an Annular Eclipse visible across America on May 10, 1994. While that path crossed the whole continent, the eclipse was not total.

      Astronomers (Then Astrologers) have been accurately predicting eclipse circumstances for centuries.  The Chinese have been able to predict them since about the year 8 BC and perhaps earlier.
      The Antikythera mechanism recovered off the coast of Greece is believed to predict astronomical positions and possibly eclipse circumstances.

      Today, Astronomers can use highly accurate data from Japanese Space Agency "Kaguya" mission's 3D scans of the Moon's surface to predict eclipse circumstances with incredible accuracy.

      Different computations use different data.  Some use an average for the moon's shape, while other systems use exact 3 Dimensional data collected by astronomical observations or new 3D Kaguya scan data. Calculations on HowToEclipse.com use google map location data including site altitude and the 3D lunar scans to compute contact times. Other sources' contact times may vary.