Edward M. Murphy

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Eclipses

• Edward M. Murphy
• Space Science for Teachers
• 2005

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Eclipses

• Although the Sun is about 400 times larger than
  the Moon, it is also about 400 times further
  away.
• Both appear to be about ½ degree across.
• As a result of this coincidence, the Moon can
  completely cover the Sun, producing a total solar
  eclipse.

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Eclipses

• The shadow of any body consists of two parts
• The umbra is where the Sun is completely blocked
  from view.
• The penumbra is where the Sun is only partially
  blocked.

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Shadows and Eclipses
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Total Solar Eclipse
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Solar Eclipse

• Under the most favorable conditions, the diameter
  of the shadow cone is 269 km at the Earths
  surface.
• At the equator, the shadow moves at 1730 km/hr.
• Totality can last as long as 7½ minutes.
• A total solar eclipse occurs about once every 18
  months somewhere in the world.
• At any given location, a total solar eclipse
  occurs once every 360 years.
• The next total solar eclipse in the U.S. is on
  Aug. 21 2017.

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Total Solar Eclipse
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Diamond Ring Effect
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Baileys Beads
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Solar Corona During Eclipse
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Total Solar Eclipse

• As the Moon orbits the Earth, its apparent size
  varies.
• Only when the Moon is closest to the Earth can it
  completely block the Sun.
• If the Moon does not completely cover the Sun we
  get an annular eclipse.

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Perigee Apogee
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Annular Solar Eclipse
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Frequency of Solar Eclipses

• We do not get solar eclipses at every new moon
  because the orbit of the Moon is tilted by about
  5 degrees with respect to the ecliptic.
• At most new moons the Moon is either above or
  below the Sun.
• The tilted orbit of the Moon crosses the ecliptic
  at two points. When the Sun approaches these
  points, eclipses are possible. This will happen
  twice a year.

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Lunar Eclipses

• A lunar eclipse occurs when the Moon passes into
  the shadow of the Earth.
• The lunar eclipse is visible to everyone on the
  night side of the Earth.
• Aristotle (384-322 B.C.) used the apparent shape
  of the Earths shadow to show that the Earth is a
  sphere.

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Lunar Eclipse
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Lunar Eclipse
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Lunar Eclipse Showing Earths Shadow
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NASA Eclipse Page

• The best web page on eclipses is
• http//sunearth.gsfc.nasa.gov/eclipse/eclipse.html