Jason Kendall's Introductory Astronomy Course

Adjunct faculty in Astronomy at CUNY Hunter (2015-2018) and William Paterson University (2011-2020)
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What is a Solar Eclipse?

How do Solar Eclipses arise? What causes them? How do you see them? Why don't you see them every month? What's the difference between total, partial, and annular eclipses? When are the ones coming up in the USA? When and where can you see them in the future all over the world? How can you safely view an eclipse?

Lecture Notes for This Video

Module 1: Foundations of Observational Astronomy: The Moon, the Seasons, and Mapping the Sky

  1. Navigating the Night Sky
  2. Angular Measurements and the Celestial Sphere
  3. The Celestial Sphere
  4. What Causes the Seasons?
  5. Lunar Phases and Months
  6. Lunar Eclipses
  7. What is a Solar Eclipse?
  8. Watching the Total Solar Eclipse of August 21, 2017
  9. Cosmic Distances using Parallax
  10. How do we know that the Earth is Round?
  11. How Big are the Sun and Moon?
  12. Geocentrism is False

Video Transcript

00:00:00:00 - 00:00:29:23
We start again now with total solar eclipses. The solar eclipse is when the moon covers the sun, and solar eclipses are partial, when only part of the sun is blocked and total when it's all is blocked. And we call them annular. Not because they happen every year. Annular eclipses when they make an annulus which is a ring or it's total like in this image from 2017.

00:00:29:25 - 00:00:56:20
The reason eclipses don't happen every month is because the orbital plane of the moon's orbit with respect to the Earth's orbit around the sun is tilted by about 5.2 degrees. That means that the shadow of the moon does not always come across the Earth's face at full, at New Moon. So you see on the left hand side, that's the position of the moon for new moon.

00:00:56:22 - 00:01:15:26
If we're looking across the plane of the Earth's orbit and the moon is in exactly the same direction as the sun, except it's inclined away and up by five degrees. And there would be a new moon that is in the direction of the sun, but above it, in the sky. And there will be no eclipse at that time.

00:01:15:29 - 00:01:40:26
So let's see when we get eclipses. These are called Eclipse seasons. And this diagram is really not to scale. There's a time of year during which the solar and lunar eclipses are possible. Lunar eclipses don't occur at every full moon, and solar eclipses don't occur at every new moon. And that's, again, because the moon's orbit is tilted five degrees with respect to the Earth's orbit and the eclipses.

00:01:41:01 - 00:02:03:19
For total solar eclipses can only occur if the sun, moon and earth are in a direct line. So because of that tilt, sometimes it's above the plane of the of the Earth's orbit and you're not going to get an eclipse there. And sometimes it's below the plane of the Earth's orbit. You're not going to get Eclipse there either.

00:02:03:21 - 00:02:33:08
But it might happen when the when the moon is at the node of the intersection between the ecliptic, the path that the earth takes around the sun and the moon's orbit around in its orbit. So those are two planes and they intersect in the line. And we call that the line of nodes. And so if the moon is new and at a node and at the ascending node, then it will be a total solar eclipse.

00:02:33:08 - 00:02:52:09
If it's exactly at that node and the node is lined up. So we have what's called is this a G? And this is a G, Is the conjunction in the sky viewed from behind, say, the moon, earth and sun. All right. But this doesn't always happen when the line of nodes is in this position. The moon might be at some other phase.

00:02:52:09 - 00:03:12:00
It might be somewhere else. It has to be at this position and it can be at any of these positions. And that's why it doesn't happen all the time. So this diagram is kind of deceptive because it makes it look like that the moon is always at this one place at this time. It's not. It can be when the nodes intersect, it could be anywhere on that orbit.

00:03:12:04 - 00:03:42:24
It just has to be at that place. Likewise, it could also be here. Actually, it happens three times a year because the direct kinetic month, which is the month according to the line of Node, is it actually that node line recesses within a period of about 18.6 years in the opposite direction of the moon's orbit. Therefore, the germinating month is faster and therefore the line of noise nodes will point at the sun three times a year.

00:03:42:26 - 00:04:08:28
And if the moon is at is exact only at New Moon at when, when, when the nodes are lined up, then sure we'll get an eclipse. The total solar eclipse. So let's look at what that looks like. A total and partial solar eclipse happens when the shadow of the moon lands on the earth. The black spot is the only place on earth where you will see a total eclipse.

00:04:09:06 - 00:04:35:07
The gray spot is where you'll see a partial eclipse. So it's the dark gray triangle that's going to cast a is called the Umbra, and that is the darkest spot in the moon's shadow. When the where the sun. If you're anywhere in the umbra, the sun is completely covered. If you're behind the moon, but if you're in the larger great triangle, you're in the penumbra, which is wider and the sun is partially covered.

00:04:35:09 - 00:04:57:08
All right. The other thing that it can be is an annular eclipse. And again, annular eclipses do not mean that they can happen annual every year annually. It means that it is an annulus, and annulus is another name for a round ring. Annular eclipses are a special form of partial eclipse, where the moon is too far away to fully cover the sun.

00:04:57:10 - 00:05:19:27
Wait a second. How is this happening? That's because the moon's orbit is elliptical. And so sometimes it's farther and sometimes it's nearer. So the moon has to be at at its closest point in its orbit in order to have a total solar eclipse. If it's at its farthest point in its orbit, then it will be an annular eclipse.

00:05:19:29 - 00:05:42:02
So we have kind of three regions. Again, the umbra is the darkest triangle. And so if you have a spacecraft and you're out in space and you're right in there, you're going to see an eclipse. The whitish triangle is where the two penumbral triangles merge and it's not fully covered. All of these things are penumbral eclipses. It's just a really special form of the penumbra.

00:05:42:02 - 00:06:15:29
Taylor. I'm glad to know that humble Penumbral Penumbral eclipse where the sun is partially covered. But this. But the moon makes a very large spot that almost covers the entire sun. Next we have the shape of the shadows on the sides of the earth. If the moon is is pointing straight overhead, there will be a pure circle. But because the earth is a sphere and it's not flat, it's because it's a sphere.

00:06:16:01 - 00:06:43:12
The shape of the shadow of the moon will be spread out across a spherical surface. And so it won't be a circle. It will be an oval. So yet another way we can determine that the Earth is a sphere. Take that Flat-earthers. Let's look at some future eclipse tracks. There's one coming up in April 8th of 2024. That's not far from today when I'm recording this.

00:06:43:12 - 00:07:04:11
But you're probably. It's possible that you'll be watching this. Well, after that time, in any event, that will be a huge, huge thing. But if you miss it, there will also be one in 2034, 2044 and 2045. So watch for those if you happen to missed the one in 2024. Here's another one nine years later and then ten years after that.

00:07:04:17 - 00:07:32:17
And then right one year later again, the 2033 one that's only in Alaska, the 2044 one is most is in northern Canada. So you're going have to take a trip. And unfortunately for caps for people who wish to see that one, they'll probably be cloudy. That's usually how that flies. Just have to wait till 20, 45, 20 more years from the time of this recording, 21 years to get another one that'll pass straight across the United States.

00:07:32:20 - 00:07:57:21
And if you love to go even further and you're a little person when you're hearing this, a tiny baby boy or baby girl, then you may get to see these much farther in the future. And in this deep, deep, deep future, I believe in 2099 is the farthest one out that will pass across there. So the United States will get a bunch in the next in the coming times.

00:07:57:23 - 00:08:18:11
But you may have to wait a very long time to see them if you don't wish to leave the continental United States in North America. Well, let's see what's happening in the rest of the world and the rest of the world. We have a lot of upcoming eclipses in this diagram. The red ones are annular and the blue ones are total.

00:08:18:13 - 00:08:50:23
And if we see the then August 2nd of 2027 going straight across the middle there from kind of going from an up to down, it first comes through the Straits of Gibraltar and then passes across northern Africa and down through I believe that's going through Egypt and Cairo, which is amazing. So that would be great. So go the there will be some amazing pictures of the eclipses from the eclipse, possibly from the from the pyramids way out there in the in the Egyptian desert.

00:08:51:00 - 00:09:13:26
And we'll also see some beautiful, beautiful images coming in from the Strait of Gibraltar and Spain. And then there's also one that kind of goes lower to up. That's in March 20th, March 20th, 2034. That will be going across central Africa and going across the hottest parts of the Saudi desert and into Iran and into Afghanistan before it gets to western China.

00:09:13:28 - 00:09:41:00
That'll be amazing. So perhaps that's something other people will see. Maybe you get the chance to see it. Take a flight. Next, let's go across and notice something truly fascinating 20, 28, 2030, 20, 37, and 2038. Australia gets four eclipses in ten years. Wow. That's going to be amazing for them. And November 25th, South Africa gets it as well.

00:09:41:08 - 00:10:01:15
But amazing that Australia gets four in the coming decade. So in the next 14 years, from the time of this recording, you'll be able to see that. And the most to me, I think that's well, the best one of all is, of course, December 26, 2038. There will be one day after Christmas, so that'll be fun for them.

00:10:01:17 - 00:10:21:00
But if you wish to, you can also take in 2039, go a little bit further south and go into Antarctica to see that total solar eclipse in Antarctica. That would be amazing. And now if we go back north, we would see August 12th of 22nd, 2026, you and North Pole to see that one or you can see it from Spain again.

00:10:21:00 - 00:10:43:28
From Spain. Amazing. Good stuff for them. And then it goes to Iceland. So that might be an amazing time to go see that and take a trip to Iceland or even Greenland, see how it goes all the way through Greenland, September 2nd of 2030 Drive. It goes through central China, North Korea and Japan. So that will be a some amazing times, which have to be a great time to be in Japan.

00:10:44:00 - 00:11:12:23
Then we go back over to North America and we see, of course, in 2033, that's the one in western Alaska and again, the one in April 8th of 2024, coming up really soon. So there's a bunch that'll happen between 2021 and 2040. And those are all all those previous maps were were given by were created by Fred ESPENAK at NASA's Jet Goddard Space Flight Center for Goddard Space Flight Center.

00:11:13:00 - 00:11:38:20
And so this is just some amazing stuff that Fred has been doing over the years. And he's a real eclipse chaser. Make sure you get a chance to see it. Got a plan for it there. They're amazing times. Why? Because you see this? Here's an image that from Glendale, Wyoming, on August 21st, 2017, taken by Vishnu Reddy. And this new was standing right behind me in Glendale.

00:11:38:20 - 00:12:01:22
And so he offered to give me these images. So this was a faint, amazing set of images. And here they are again. This is during totality. Can you see you can you see in a photographic image like this, the corona of the sun, which we talk about with the corona, is in my module about the sun. But this is what it really looks like through a camera, but it looks different.

00:12:01:25 - 00:12:27:03
Naked eye. We don't really have to. You shouldn't look at it naked eye. You should always have some sort of protection. But you do see the corona in the sky, which is amazing. That's just astonishing. It does get dark when you when it goes to totality. It's absolutely beautiful. I be showing you this in just a second. So, again, a total solar eclipse is when the and lights from the sun, the disk of the sun is completely blocked by the moon.

00:12:27:05 - 00:12:52:00
And it is interesting that the moon's size is exactly the same as the sun's the size in the sky. And we'll get to why that is later. So an annular solar eclipse here is the one that just happened on October 14th of 2023. And this is by JAXA and ESA, and it was taken by the solar telescopes, you know, day as the moon came across, it came between it and the sun.

00:12:52:02 - 00:13:16:29
And so this is from science, nasa.gov. So go there and look for this image from JAXA. Nasser next. This was taken in National Park Service by Kevin Dust Axler and October 14th and from the Desert Southwest. And this is a progression of all the images taken in together and this is the Umbral shadow is seen from space and this is a really interesting thing.

00:13:16:29 - 00:13:40:06
And I believe this was aboard the International Space Station on November 13th of 2003, and this was downloaded from NASA's Goddard Space Flight Center. When you go see an eclipse, solar eclipse, make sure you do it safely. First, look over on the left hand side. Get yourself those eclipse goggles. You need that or else you're going to you know, you damage your eyes.

00:13:40:06 - 00:14:12:00
The sun is really bright and just because the moon's covering it doesn't mean that it can't damage your eyes. And it's really wonderful to watch the moon go across the sun. And if you have these kind of glasses, you will be able to see the chunk taken out. But as it happens, also, if you're really smart, you can put a solar filter on top of a little junky telescope that you don't mind burning the interior optics off and projecting it to the side so people can watch without having to look through the little glasses where you can make a pinhole telescope like that diagram.

00:14:12:03 - 00:14:33:13
It basically is a cardboard shield with a little pinhole. And you typically want to make that pinhole out of foil. So it's a very tight pinhole. It'll is better if you put it inside some sort of box in that thing, like the kids in the middle. They're going to they will see the corona. But you would see the corona if you put the pinhole camera inside a box and then look inside the box from the side.

00:14:33:16 - 00:14:39:27
At the very minimum, if you're going to go see a solar eclipse, get some eclipse shade.