What makes an eclipse?
Name: Janette L Gubala and Andrew G Cantrell
What makes an eclipse occur?
Eclipses occur when one astronomical object gets in the way of another, so
that the second objects light is blocked from reaching the Earth. In a
solar eclipse, our Moon gets between the Earth and the Sun, and blocks the
light from it for a while. It is actually a rather remarkable coincidence
that the Moon and the Sun are roughly the same angular size right now, so
that this is possible but rare (and very spectacular). It is thought that
trying to understand and predict solar eclipses was one of the motivations
for the development of astronomy thousands of years ago. In lunar eclipses
the Earth gets between the Sun and the Moon, so that the Moon becomes darker
as we see it from Earth. There are all sorts of variations on these
eclipses where only part of the object is blocked by the other - this
happens because the orbit of the Moon is not a perfect circle and is not
quite perfectly aligned with the Earth's orbit about the Sun.
We have a new moon every 28 days. Look on some calendars and you should see
the days when the new moon is to be seen. As the Moon starts to come around
the Earth so its edge to the Sun is just visible we see a new moon. Why do
not you watch the Moon at the same time each night for a month or so and see
if you can record how it looks each day and figure out when it changes and
how fast it goes around.
Samuel P Bowen
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Update: June 2012