WEBVTT

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A total solar eclipse is
an extraordinary event.

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 For a few minutes,

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night falls in the middle of the day!

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How is this possible?

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 In astronomy,

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an eclipse occurs
when one celestial body

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moves into the
shadow of another,

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blocking out some or all of its light.

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 On Earth,

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this can happen on two occasions:

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The Moon can pass behind the Earth

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 and cross the Earth's shadow cone.

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Or the Moon can pass between
the Sun and the Earth,

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and it is the Earth that crosses
 the Moon's shadow cone.

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What do we see on Earth?

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During a lunar eclipse,

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 the observer is on the night side.

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The night is clear beacause the Moon is full.

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But suddenly

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 a shadow moves in and seems
to nibble at the moon.

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It's the Earth's shadow
blocking the sunlight.

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A total eclipse is much more impressive

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because it happens during the day.

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The moon moves slowly

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and positions itself between
the sun and our eyes.

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Its shadow is cast on the Earth.

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An observer cannot see the moon moving
in front of the Sun

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 because the Sun is much too bright.

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To see it,

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one must wear protective glasses.

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When the alignment is perfect

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 and the solar disk is completely obscured,

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darkness suddenly sets in.

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This is the only moment allowed
to remove the protective glasses

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and experience the magic
of a total solar eclipse.

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The moon covers the sun perfectly

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and a thin, bright crown surrounds it.

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 This is the solar corona.

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It's not the eclipse
that causes this appearance.

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The corona is always present.

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The occultation of the solar disk

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reveals this outer layer of
the solar atmosphere to our eyes.

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The conditions that allow you
to see a total solar eclipse are rare:

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First,

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the alignment between the Sun,
the Moon, and the observer must be perfect,

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otherwise the moon will
only cover part of the Sun.

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The sky will darken, but not completely.

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This is a partial eclipse,

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and the observer cannot remove
his protective glasses

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at any time while looking at the Sun.

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Because the Moon's orbit
is slightly elliptical,

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the distance between the Earth
and the moon varies.

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If the Moon is too far away
at the time of alignment,

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an annular eclipse is observed.

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and some brightness remains

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If the Moon is too close,

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its apparent diameter will be larger
than that of the Sun.

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The eclipse is total,
 but the solar corona is not visible.

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The last condition,

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is to be lucky enough
to be in the right place

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 on the narrow path of totality.

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Finally, an amazing coincidence

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 makes the eclipse absolutely incredible.

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 The Moon is 400 times
smaller than the Sun,

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 but it also happens to be
400 times closer.

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In other words,

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 the Earth is in the unique position

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 that allows the lunar disk to appear

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the same size as the solar disk.

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If a total solar eclipse
is happening nearby,

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you do not want to miss
such an event.

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The next one will probably be
a century later.

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And don't forget your glasses