A solar eclipse occurs when the moon moves between the Earth and
the sun, blocks the sun’s light, and casts a shadow on the Earth.
When the moon completely covers the bright disk of the sun,
that’s a total solar eclipse, and it happens roughly every
year and a half somewhere on Earth. A partial solar eclipse
is more common, happening at least twice a year. A lunar
eclipse, on the other hand, is where the moon moves behind the
Earth, so it’s now the Earth blocking the sun’s light on the
moon, creating a shadow on it with a red tint. The easy way to
remember the difference is to remember what gets darker. With
a solar eclipse, the sun gets darker, and during a lunar
eclipse, the moon does. A solar eclipse is a rare event that not
many get to see, because the moon’s shadow is relatively
small. This limits the locations on Earth that get to see it. You
have to be on the sunny side of the planet, and you have to be
in the path of the moon’s shadow. So, if you find your
area in the path of totality one year, you’ve hit the jackpot,
because on average, that same spot on Earth will only get to
see a solar eclipse every three hundred seventy-five years!
During a solar eclipse, the moon casts a shadow with two parts:
the umbra and penumbra. The moon’s umbra is the part of the moon’s
shadow where the entire sun is blocked by the moon. In space,
it’s a cone extending some four hundred thousand kilometers
behind the moon. It’s when the small end of this cone hits the
Earth that we experience a total solar eclipse. Most eclipse maps
depicting the path will show you a circle representing the
shadow of the moon, but in actuality, the true shape of the
umbra is more like an irregular polygon with slightly curved
edges. This is because the moon isn’t a perfect circle – it has
mountains and valleys on its surface, which all affect the
passing sunlight and subsequent shape of its shadow. And
scientists now have a greater understanding of the shape of
the moon’s surface, thanks to NASA’s Lunar Reconnaissance
Orbiter. The unprecedented level of detail from the topographic
maps, photos, and other datasets has allowed us to more precisely
pinpoint the regions on Earth falling within the path of
totality of a solar eclipse. So if you get the chance to witness
a solar eclipse, always remember that our little moon plays a
role that's quite large.
[beeping]