00:01A solar eclipse happens when a new moon moves between the Earth and the Sun,
00:06blocking some or all of the Sun's rays from reaching the Earth.
00:11By cosmic chance, even though the Sun is 400 times wider than the Moon,
00:16it's also 400 times farther away.
00:19Therefore, the two objects appear the same size in our sky.
00:25Astronomers are able to predict eclipses
00:28because the Earth and Moon have very predictable orbits.
00:33Why, then, isn't there an eclipse every month?
00:36The Moon's orbit is usually tilted a few degrees north or south in relation to the Earth.
00:43When the Moon does eclipse the Sun, it casts two types of shadows on Earth,
00:48a smaller, darker shadow known as the umbra
00:52and a larger shadow known as the penumbra.
00:58There are four types of solar eclipses.
01:01The first and most spectacular is a total eclipse,
01:04when the Moon completely covers the Sun's surface.
01:07A total eclipse can only be seen if you're standing within the umbral shadow.
01:12That's why the imaginary line created by this shadow as it races across Earth
01:17is known as the path of totality.
01:20People within the penumbra shadow see only a partial eclipse, the second type.
01:26From this view, outside the path of totality,
01:29the Moon passes in front of the Sun off-center, never fully covering its surface.
01:35Third, an annular eclipse occurs when the Moon passes directly in front of the Sun.
01:40However, unlike a total eclipse, the Moon appears too small to fully cover the Sun.
01:47The Moon's orbit is elliptical, so sometimes it's closer to Earth and sometimes it's farther away.
01:53Last, a hybrid eclipse, is when the Moon's position between the Earth and Sun is so finely balanced
02:01that the curvature of the Earth plays a role.
02:04The Moon will be farther away from some parts of Earth along the eclipse's path,
02:09resulting in an annular eclipse.
02:11In other parts, the Moon will be just close enough to fully cover the Sun,
02:16resulting in a total eclipse.
02:19While a total solar eclipse happens somewhere on Earth every year or two,
02:24any given point on Earth experiences the event only about once every 400 years.
02:30We interrupt this video for an important safety announcement.
02:35Looking directly at the Sun, even during an eclipse, can cause permanent eye damage.
02:41Fortunately, there are ways to enjoy an eclipse safely.
02:44The easiest is to use certified eclipse-watching glasses,
02:48which are shaded thousands of times darker than typical sunglasses.
02:52You can also look at the eclipse indirectly by making a pinhole viewer.
02:56Simply poke a small hole in a piece of cardboard.
02:59Hold the cardboard up to the Sun, allowing the Sun's image to be projected onto a flat surface.
03:05Be sure to look only at the surface and not through the cardboard.
03:09Just before the Moon completely covers the Sun,
03:12low-lying valleys on the Moon's edge will be the only spots that sunlight continues to pass through.
03:18These remaining brilliant shafts of light, known as Bailey's beads, will disappear one after another.
03:25And finally, a single bead of light remains, known as the diamond ring,
03:30signaling that you're just seconds away from experiencing totality.
03:34Once the last bead disappears, and the Moon completely covers the Sun's surface,
03:39the view through your eclipse glasses will be pitch black.
03:43Totality achieved!
03:47At this point, none of the Sun's rays are reaching your eyes,
03:50and it's the only time that it's safe to take off your glasses.
03:54Remember to put your eclipse glasses back on before any of the Sun's rays start to peek through again.
04:01Any sunlight reaching your eyes even for a few seconds can cause serious damage.
04:06While an eclipse can last a few hours, totality typically occurs for less than three minutes.
04:13Animals and plants have also been known to alter their behavior during a total eclipse.
04:19Songbirds may stop singing, crickets may start chirping, and flowers may even start to close up.
04:26We won't always be able to see total solar eclipses.
04:31The Moon moves about one and a half inches away from Earth each year.
04:35It's estimated that in about a billion years,
04:38the Moon will be too far away from Earth to completely cover the Sun.
04:42Unlike the Moon,
04:57you third remember the Moon will ever see the Moon's surge in the Moon.
05:02You can imagine that in about a billion years when recording it,
