Solar Eclipses

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Solar Eclipses
Solar Eclipses
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Solar eclipses the big picture
This drawing shows how the Sun, moon and Earth
line up during a solar eclipse. The shadow area
where you could see a total eclipse is only 92
miles wide. If the entire Sun appears covered by
the moon, this is called a total eclipse if only
part, then it is a partial eclipse.
Click here to see an eclipse animation
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What do eclipses look like?

• Below you see an illustration of a total
  eclipse as seen from Earth. The entire process
  lasts only less than two hours, with the whole
  Sun blocked for up to eight minutes or less. Just
  during totality the corona seems to glow around
  the edges of the moon. Total eclipses occur
  somewhere on Earth only about once every 18
  months.

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Why dont eclipses happen every month?

• At first thought, it would seem that we should
  have an eclipse each month when the moon passes
  between the Sun and the Earth. Why not?
• The answer lies in the slight tilt (5o) of the
  Moons path in relation to the Earths path. It
  is usually above or below the direct sight line
  to the Sun.

Earth
Sun-Earth line
Moons tilted orbit
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Total solar eclipse video

• This video of the June 21, 2001 eclipse seen in
  Africa shows the Sun just as it is going into
  totality

Click on image to play video
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Time series of an eclipse

• This series of photos shows a entire total solar
  eclipse, from beginning to end, in a series of
  pictures taken by the same camera over about a
  two hour period.

Credit Dennis Mammana
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Partial eclipses

• From some places on the ground, viewers of
  eclipses only see part of the Sun covered by the
  Moon. They see what we call a a partial eclipse.
  Many more people see partial eclipses than total
  eclipses because the shadows path of the Moon
  for this is many times broader.

Credit Fred Espenak
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Eclipse shadows

• When the light passes through gaps between
  leaves of a tree, the shadows on the ground show
  little copies of the eclipse going on in the sky.
  In this eclipse, the moon did not quite cover all
  of the Sun, so you seen white rings.

Credit Ruth Benn
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Total eclipse photos
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Watching a total eclipse . . .

• As the crescent of light disappears, tiny
  specks of light are visible around the edge of
  the Sun. These specks of light are called
  Bailey's Beads and are the last rays of sunlight
  shining through the valleys on the edge of the
  Moon.
• Suddenly the sky is dark, but if you look
  toward the horizon you will see a reddish glow
  like a sunset. Once the Sun is totally eclipsed,
  the Sun's corona can be seen shining in all
  directions around the Moon. This is a spectacular
  sight because the only time the Sun's corona can
  be seen is during a total solar eclipse.
  Temperatures begin to fall.
• Also visible during a total solar eclipse are
  colorful lights from the Sun's chromosphere and
  solar prominences shooting out through the Sun's
  atmosphere. Without sunlight, bright stars and
  planets can be seen from the areas on earth in
  the Moon's shadow.

Baileys Beads appearing just after totality
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Why do scientists care?

• Free from the blinding glare from the Sun itself,
  the corona that surrounds it is usually the prime
  target for the observations. So during an
  eclipse, expeditions go out to whatever sites
  seem most favorable, to capture what may be a
  once-in-a-lifetime observation of things that are
  otherwise hidden by the Suns brightness.
• A NASA spacecraft called SOHO creates a false
  eclipse with its coronograph instrument and
  observes the Sun all day, everyday. Its
  observations can be compared with others on Earth
  during an eclipse to learn even more about them.

An image of the Sun was placed on top of an
eclipse image, which was centered on a
coronagraph showing the extended corona (June 21,
2001)
Eclipse image Williams College