Name: 什麼是日食？|| 日食｜｜月食｜｜天文學 (What are Eclipses? || Solar Eclipse || Lunar Eclipse || Astronomy)
Uploaded: 2021-01-14T08:51:16.000Z
Duration: 9 min 3 s
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Maybe even a little unsettling, but, you knew it was only going to last for a short time.

It must have been terrifying for early mankind.

Your faithful companion in the sky just up and disappears.

It would have felt like the world was ending.

Even now, with all we know, an eclipse is one of the most dramatic celestial events

We’re a little more blasé about astronomical events these days.

We use powerful telescopes to peer at the distant reaches of space, capturing not just

visible light, but all kinds of radiation - and we get back the most beautiful pictures.

We can see nebulae…... even supernovas.

But we still get pretty excited for eclipses that we experience firsthand,

You may be a little fuzzy on the details.

You know an eclipse has something to do with the Earth getting in the way of the moon -- or,

is it the moon getting in the way of the Sun?

Which is for a Solar Eclipse, and which is for a Lunar Eclipse?

Sometimes, the Sun, the Earth, and the Moon all line up along a straight line.

When the Earth is in the middle, the shadow of the Earth can fall on the moon, which is

OR, in the other arrangement, with the moon in the middle, the shadow of the moon can

fall on the Earth, which is a Solar Eclipse.

Notice that these eclipses only happen during a new moon (in the case of a solar eclipse)

or a full moon (in the case of a lunar eclipse).

But why don’t these happen every single month?

You know that the moon orbits the Earth, and the Earth orbits the Sun.

But these orbits don’t take place in the same PLANE.

There’s a difference of about 5 degrees between the plane of the Earth’s orbit and

The two orbital planes intersect along what we call the “line of nodes.”

It’s only when the Sun, Earth, and Moon all line up juuust right along the line of

The plane of the Earth’s orbit is called the ECLIPTIC plane.

This name comes from the path we see the Sun take across the sky - the “Ecliptic”.

Of course, it’s actually the Earth moving around the Sun, but from our perspective on

Earth, it LOOKS like the Sun is moving in a fixed path across the sky.

This idea dates back to the ancient concept of a “Celestial Sphere.”

The Greek scholars of antiquity proposed the heavens consisted of concentric, crystalline

The Sun, the Moon, and other planets were each thought to have their own invisible sphere

that could freely rotate, and the distant stars were fixed in place

The “Celestial Sphere” is still a useful way to picture our heavens.

To an observer on Earth, all celestial objects, no matter their distance, appear projected

on the inner surface of the Celestial Sphere - as if we were living under a dome.

Elements of spherical astronomy are still used today whenever we look for celestial

objects based on a particular date, time, and position on Earth.

During an eclipse, the Moon happens to land along the Sun’s apparent path across the

sky - the “Ecliptic.”That’s why we call it an “eclipse.”

During a Full Moon, The Sun and the moon are on opposite sides of the Earth.

A lunar eclipse happens during a Full Moon if the moon is on the line of nodes and the

Sun is also on or near the line of nodes.

Now all three celestial bodies are in a straight line, and the shadow of the Earth

By contrast, the moon comes between the Sun and the Earth in a New Moon.

This is when a Solar Eclipse is possible.

These happen less frequently than Lunar Eclipses.

What’s more, it’s much harder for an observer on Earth to see a solar Eclipse

A lunar eclipse is visible everywhere in the world - as long as it’s not cloudy.

If you can see the moon, you can see a lunar eclipse.

A solar eclipse, on the other hand, is only visible along a particular path - the path

If you stand right in the center of the moon’s shadow (the umbra) you will be able to see

But if you’re in the penumbra, this weaker, outer shadow, you’ll only see

The farther away from the path of totality, the smaller the degree of eclipse you’ll

There’s another reason why total solar eclipses are rare.

Remember that the Moon’s orbit is elliptical.

That means there are times when the moon is closer to Earth, and times

The farther the moon is from the Earth, the smaller it appears.

When the moon is at its farthest from the Earth, we call it apogee.

Under these conditions, even if everything else is right for a solar eclipse, you can

see the Sun peeking out from around the moon.

We call this an ANNULAR solar eclipse, named for the ring of fire around the moon.

In these kinds of Eclipses, the Moon is so far away, its umbral shadow doesn’t reach

But when the moon is closer to the Earth, that’s our chance for a total Solar Eclipse.

The moon looks bigger in the sky - big enough to cover up the Sun.

You don’t look right at the sun on a normal day, right?

Well, the sun’s rays don’t change during an eclipse.

Get yourself a handy dandy set of eclipse glasses for everyone in your family.

They even make clip-ons for people who wear prescription glasses.

Get yourself some genuine eclipse glasses.

We’ll include a link in the description so you can get your own. These are mine.

Here’s what you’ll get to see during a Solar Eclipse if you’re lucky enough to

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什麼是日食？|| 日食｜｜月食｜｜天文學 (What are Eclipses? || Solar Eclipse || Lunar Eclipse || Astronomy)

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