A solar eclipse is when the Moon lines up between Earth and the Sun such that the Moon either partially or completely blocks out the Sun.

Eclipse Across America

For the first time since 1979, the contiguous United States will be treated to a total solar eclipse. Even more exciting, the path of totality across the USA starts in Oregon and ends in South Carolina.

Total Solar Eclipse – August 21, 2017

Eclipse flyer by NASA
NASA - What can you see during a total solar eclipse?

CREDIT: Exploratorium

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Partial Eclipses

When the Sun is completely blocked out we called it a total solar eclipse, and often this is what people think of with an eclipse. But a partial eclipse can be just as exciting.

When the Moon comes just shy of completely blocking out the Sun a bright ring or annulus is visible.
This is a special kind of partial eclipse, an annular eclipse.

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How can I view the eclipse safely?

The most important this to remember is that it is never safe to look directly at the uneclipsed or partially eclipsed sun without the proper safety glasses. The only time you can look at the sun without safety glasses is during the brief moments of totality. There is a lot of great information at NASA and the AAS (American Astronomical Society) about how to safely look directly at the sun as well as indirectly. For all these points and more check out:

NASA eye safety
Eclipse projector
Eclipse mirror


Eclipse/Transit Facts

  • The longest duration for a total solar eclipse is 7.5 minutes.
  • Eclipse shadows travel at 1,100 miles per hour at the equator and up to 5,000 miles per hour near the poles.
  • The maximum number of solar eclipses (partial, annular, or total) is 5 per year.
  • A total eclipse can only happen during a new moon.
  • Nearly identical eclipses (total, annual, or partial) occur after 18 years and 11 days, or every 6,585.32 days (Saros Cycle).
  • A total solar eclipse is not noticable until the Sun is more than 90 percent covered by the Moon. At 99 percent coverage, daytime lighting resembles local twilight.
  • The width of the Moon’s shadow is at most 170 miles wide.
  • There are at least 2 solar eclipses per year somewhere on the Earth.
  • Total solar eclipses happen about once every year or two.
  • The Sun’s corona (“crown”) can ONLY be seen from the Earth’s surface during a total eclipse.
  • The alignment of Sun, Venus, and Earth comes in pairs that are eight years apart but separated by over a century.
  • The last transit of Venus pair before 2012 happened in December 1874 and December 1882.
  • The most recent pair were in June 2004 and June 2012.
  • After 2012, subsequent pairs will be in December 2117 and December 2125.
  • There will be 36 solar eclipses from 2001-2025, of which 15 will be total eclipses on some part of Earth’s surface – a little less than the average of one a year.
  • Transits and eclipses are rare celestial events but the transit of Venus is the rarest.
  • Transits of Venus allow astronomers to calculate more accurately the distance of Venus from the Sun, and subsequently the distances of other planets.
  • One can see the corona or atmosphere of the Sun safely with naked eyes only during a total solar eclipse.
  • Gemini 12 witnessed a total solar eclipse in 1966 and the International Space Station, in 2006.
  • The Hubble Space Telescope will be aimed at the moon to detect dips in brightness during the 2012 transit of Venus.
  • The Solar Dynamic Observatory captured the Sun and Venus during the 2012 transit in unprecedented detail.
  • A transit of Venus occurs when Venus passes directly between the Sun and the Earth.
  • A solar eclipse occurs when the moon passes between the Sun and the Earth, and the moon fully or partially blocks the Sun as viewed from a location on Earth.
Total Lunar Eclipse of April 15, 2014 from

Guide to Solar Eclipses (Infographic) Guide to Solar Eclipses (Infographic)

Credit: Karl Tate, Contributor
How Solar Eclipses Work: When the moon covers up the sun,
skywatchers delight in the opportunity to see a rare spectacle.