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Little
Known Facts About Solar Eclipses
- The longest
duration for a total solar eclipse is 7.5 minutes.
- 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.
- Eclipse
shadows travel at 1,100 miles per hour at the equator and up
to 5,000 miles per hour near the poles.
- The width
of the path of totality is at most 167 miles wide.
- The maximum
number of solar eclipses (partial, annular, or total) is 5 per
year.
- There
are at least 2 solar eclipses per year somewhere on the Earth.
- Only partial
solar eclipses can be observed from the North and South Poles.
- Total
solar eclipses happen about once every 1.5 years.
-
Nearly
identical eclipses (total, annual, or partial) occur after
18 years and 11 days, or every 6,585.32 days (Saros Cycle).
- The Saros
Cycle exists because it takes 18 years and 10 days for the entire
orbit of the Moon to precess once around in its orbit plane
so that the lunar nodes make one complete revolution along the
orbit. This "Nordical" period equals nearly an integer
number of lunar months (223 x 29.53 days = 6,585.19 days) during
each Saros Cycle. Because the true length of the Saros Cycle
is 6,585.32 days, you have to wait THREE Saros Cycles in order
for an eclipse to repeat at the same spot on Earth.
- Successive
eclipses in the Saros Cycle happen 1/3 of the way around the
world from each other, and after three Saros Cycles, the eclipse
returns to nearly the same geographic location after 54 years
and 33 days.
- Twelve
different Grand Saros eclipse series are now occurring, with
the one producing the eclipses of 1937, 1955, 1973, 1991, and
2009 having durations near the 7.5 minute limit.
- Every
eclipse begins at sunrise at some point in its track and ends
at sunset about half way around the world from the start point.
- Partial
solar eclipses can be seen up to 3,000 miles from the track
of totality.
- Before
the advent of modern atomic clocks, studies of ancient records
of solar eclipses allowed astronomers to detect a 0.001 second
per century slowing down in Earth's rotation.
- Total
solar eclipses happen because the Sun is near one of the nodes
of the lunar orbit, and the Moon is at perigee at this node
at the same time.
- Annular
solar eclipses happen because the Sun is near one of the nodes
of the lunar orbit, and the Moon is at apogee at this node at
the same time.
- Shadow
bands are often seen on the ground as totality approaches.
- Light
filtering through leaves on trees casts crescent shadows as
totality approaches.
- Local
animals and birds often prepare for sleep or behave confusedly
during totality.
- Local
temperatures often drop 20 degrees or more near totality.
- During
totality, the horizon is illuminated in a narrow band of light,
because an observer is seeing distant localities not under the
direct umbra of the Moon's shadow.
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7.5
minutes is the longest duration for
a total solar eclipse.

Eclipse
shadows travel at 5,000 mph at the poles, and 1,100 mph at the
equator.

The
width of a path of totality is 167 miles wide.

Local
animals prepare for sleep or act confused during totality.

Temperatures
drop 20 degrees or more at totality.

The
horizon glows from distant localities not under the direct umbra.
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