- [Narrator] A solar eclipse happens
when a new moon moves between
the Earth and the sun,
blocking some or all of the sun's rays
from reaching the Earth.
By cosmic chance, even though the sun
is 400 times wider than the moon,
it's also 400 times farther away.
Therefore, the two objects
appear the same size in our sky.
Astronomers are able to predict eclipses
because the Earth and moon
have very predictable orbits.
Why, then, isn't there
an eclipse every month?
The moon's orbit is usually tilted
a few degrees north or south
in relation to the Earth.
When the moon does eclipse the sun,
it casts two types of shadows on Earth:
a smaller, darker shadow,
known as the umbra,
and a larger shadow,
known as the penumbra.
There are four types of solar eclipses.
The first and most spectacular
is a total eclipse,
when the moon completely
covers the sun's surface.
A total eclipse can only be seen
if you're standing
within the umbral shadow.
That's why the imaginary
line created by this shadow
as it races across Earth is
known as the path of totality.
People within the penumbral shadow
see only a partial
eclipse, the second type.
From this view, outside
the path of totality,
the moon passes in front
of the sun off-center,
never fully covering its surface.
Third, an annular eclipse,
occurs when the moon passes
directly in front of the sun.
However, unlike a total eclipse,
the moon appears too small
to fully cover the sun.
The moon's orbit is elliptical,
so sometimes it's closer to Earth
and sometimes it's farther away.
Last, a hybrid eclipse, is
when the moon's position
between the Earth and
sun is so finely balanced
that the curvature of
the Earth plays a role.
The moon will be farther
away from some parts of Earth
along the eclipse's path,
resulting in an annular eclipse.
In other parts, the moon
will be just close enough
to fully cover the sun,
resulting in a total eclipse.
While a total solar eclipse happens
somewhere on Earth every year or two,
any given point on Earth
experiences the event
only about once every 400 years.
(high-pitched hum)
(static crackles)
We interrupt this video
for an important safety announcement.
Looking directly at the sun,
even during an eclipse, can
cause permanent eye damage.
Fortunately, there are ways
to enjoy an eclipse safely.
The easiest is to use certified
eclipse-watching glasses,
which are shaded thousands of times darker
than typical sunglasses.
You can also look at
the eclipse indirectly
by making a pinhole viewer.
Simply poke a small hole
in a piece of cardboard.
Hold the cardboard up to the sun,
allowing the sun's image to be projected
onto a flat surface.
Be sure to look only at the surface
and not through the cardboard.
Just before the moon
completely covers the sun,
low-lying valleys on the moon's
edge will be the only spots
that sunlight continues to pass through.
These remaining brilliant shafts of light,
known as Baily's beads, will
disappear one after another.
And finally, a single
bead of light remains,
known as the Diamond Ring,
signaling that you're just seconds away
from experiencing totality.
Once the last bead disappears
and the moon completely
covers the sun's surface,
the view through your eclipse
glasses will be pitch black.
Totality achieved.
At this point, none of the sun's
rays are reaching your eyes
and it's the only time that it's safe
to take off your glasses.
Remember to put your
eclipse glasses back on
before any of the sun's rays
start to peek through again.
Any sunlight reaching your
eyes, even for a few seconds,
can cause serious damage.
While an eclipse can last a few hours,
totality typically occurs
for less than three minutes.
Animals and plants have also been known
to alter their behavior
during a total eclipse.
Songbirds may stop singing,
crickets may start chirping,
and flowers might even start to close up.
We won't always be able to
see total solar eclipses.
The moon moves about one
and a half inches away
from Earth each year.
It's estimated that in
about a billion years,
the moon will be too far away from Earth
to completely cover the sun.
(elegant music)
