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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Lunar Eclipses

In this video, I discuss the motions of the Moon, the reason for, and types of Lunar eclipses. I also have some some pictures I took of some lunar eclipses.

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 - 00:00:32:07
Now we're going to be talking about lunar eclipses. This is a video I took on October 8th of 2014 at about 5:00 in the morning from a park in northern Manhattan. This is the beginning of a total lunar eclipse that was visible in New York City. there goes a plane there. That eclipses are truly fascinating things. You can see here that the shadow of the earth is marking across the moon in a way that you don't see with the phases of the moon.

00:00:32:10 - 00:00:53:21
This eventually developed into a full, total lunar eclipse. But unfortunately for New York City, on that date, the moon was set before totality. So now let's take a look at what we can see when lunar eclipses occur where the moon passes into the earth's shadow. These are three exposures of the moon taken before, during and after a total lunar eclipse.

00:00:53:28 - 00:01:18:18
And specifically, this is the one on September 27, 1996. And that was kind of an interesting one for me, because I was at a Broadway show that night, Christopher, during Sex and Longing, starring Sigourney Weaver. And during intermission, everybody went outside to look up at the lunar eclipse. And it was fascinating to see that over Broadway. So we all stood in the street.

00:01:18:18 - 00:01:42:14
We looked up, but then the bell rang for the second act, and my brother really wanted to go back to see the show. So back we all went did it. Luckily, the show was really good. But we were able to catch the rest of the lunar eclipse after the show. So let's look at more about lunar eclipses. So if you have a penumbral lunar eclipse, here's the configuration.

00:01:42:16 - 00:02:20:01
So the moon has to get into into the Earth's shadow. And so this is, of course, really not to scale. Really, really not to scale. I'm showing some lines at the boundary of the lines that do mark the umbra or the darkest parts of the Earth's shadow from the sun. And this is anywhere in the umbra, the earth is completely blocking out all the light of the sun, the penumbra that the sun is not completely blocked out by the earth when it's in the penumbra, like we saw in the beginning of the event or at the beginning.

00:02:20:04 - 00:02:41:29
There was a chunk taken out and that was still in the penumbra. The chunk that seemed to be fully taken out was in the umbra. So as time progressed, it certainly looked more and more like it was going into the umbra. The penumbra just looks a little dimmer, but the umbra extraordinarily dark. So if we go ahead a little bit more in time as the moon goes around in its orbit.

00:02:42:01 - 00:03:02:06
If it passes fully into the umbra, then it's called a total lunar eclipse. Sometimes it just has a partial lunar eclipse like we saw at the beginning. That would be considered a partial if the moon just did that. And that happens frequently as well. All right. So let's look at the different kinds of eclipses that the moon can have.

00:03:02:09 - 00:03:29:02
And they are the tandem role, which is at the top. And then we have the partial eclipses which are at the bottom. Those would be a partial just like that. We see a little bit of dimming, but then there's more dimming because it goes in the pin in the umbra, just like we saw at the beginning. And then finally, a total lunar eclipse where the moon passes completely into the umbral shadow of the earth.

00:03:29:04 - 00:04:01:11
Now, it's also important to note that these don't happen every month. They don't. And the reason is, is because the moon's orbit is tilted five degrees with respect to the Earth's orbit around the sun. So the moon's orbit does not. So the moon doesn't always pass through the shadow. And therefore we have to look for eclipses during eclipses seasons and eclipse seasons are when the line of nodes, which is that red line lines up.

00:04:01:14 - 00:04:34:14
So let's see what we have because of this tilt of the of the of Moon's orbit respect to the earth's orbit around the sun. They simply don't happen every month because of that tilt. And the ecliptic is the path that's the big blue area. But the tilt is the tilt of the moon's orbit. So at this time in the moon's orbit, if the moon's orbit around the around the sun, there will be no way at any time for there to be a lunar eclipse because the line of nodes does not point to the sun.

00:04:34:16 - 00:04:59:08
Now, if we go across, say to six months later, again, there won't be any eclipses there because the the the moon is either below the ecliptic or above it. And now if we get to this point in the when the nodes line up and point at the sun, they can happen here. The red line is called the line of nodes.

00:04:59:08 - 00:05:22:11
And this is the intersection where the moon's orbit intersects with the ecliptic. However, it might not happen if the full moon, if the moon is not at the line of nodes for, say, a new moon. So if it's not in new moon phase and you won't get a total solar eclipse, and if it's not a full moon, you won't get a total or even partial or even penumbral lunar eclipse.

00:05:22:18 - 00:05:44:09
So the moon has to be at the line of Mode's line of nodes on that day. And likewise six months later, it can certainly might happen there too. But it certainly seems a little weird because it looks like I'm drawing it, that they're always at the same time. So you should be able to line this up. However, the line of nodes also processes.

00:05:44:11 - 00:06:34:21
So that means the location on the is location changes with time. So really after about a year, it's more like that. So the line of nodes gets back to its position prior to 365.25 days. And so you can have three line ups of the line of nodes during a calendar year. And that's because the Dragon knitting month, which which is the month, according to the the line of nodes, when it gets away from the one ascending node to one descending node that happens that happens in a 27.2 days compared to say the calendar month or the or the the month according to the phases, which is about 29 days.

00:06:34:23 - 00:07:02:12
Now, the line of nodes itself processes with a period of 18.6 years. So that whole that whole plane will make one full kind of swing around every 18 years. Therefore, we do know that the line of nodes will point to the sun roughly three times a year. So that's a bit about lunar eclipses. And I'd like to show you some wonderful pictures that I took.

00:07:02:14 - 00:07:29:07
The first one is this is a series of photos from Inwood Hill Park in New York City. This is a total lunar eclipse. I took these pictures on October 8th of 2014 at about 5:00 in the morning. And you can see the time is progressing and it's getting more and more and more covered as time goes on. And it was about 558 in the morning when I had to start packing it in because it was getting close to sunrise.

00:07:29:07 - 00:07:51:05
The moon was setting fast. It was also getting really cloudy, as you saw in the video at the beginning. And this started roughly about 5:00 in the morning and it progresses rapidly over about an hour. So I'm just going to give you a different one. This is from September 27 of 2015. And I took this one, too. This was near the end of the eclipse.

00:07:51:11 - 00:08:17:03
This was about 10:00 PM on September 27th of 226, 2015. It's a begs the question, why are total lunar eclipses all red? Well, total lunar eclipses, when you go out and see them, they look deep, deep red. It's like, why would they look really red? And so the answer is because we're looking at the refracted light from a ring of sunsets.

00:08:17:06 - 00:08:51:14
If you were on the moon looking up at the Earth during a total lunar eclipse, unlike a solar eclipse because the moon has no atmosphere during a solar eclipse, you see the atmosphere of the sun and you can see which we'll talk about in another video about total solar eclipses. But in a total lunar eclipse, if you were looking from the moon back to the earth, you would see the atmosphere of the earth glowing red because the Earth's atmosphere scatters blue light better than red.

00:08:51:16 - 00:09:12:04
So the light that gets passed through on this ring around the earth, that's that that would be the atmosphere that we would you would see if you were on the moon looking towards the earth, it would look this bright, bright, bright red. And that would makes the that the the the moon's light and is illuminated by this refracted red light.

00:09:12:06 - 00:09:44:14
And so the deeper it goes into the umbra of the Earth's shadow, the redder it becomes and it gets dead center inside of the umbra. It becomes this deep, deep red and it's quite gorgeous. I've seen that a few times, too. It's absolutely spectacular. So that's a bit about lunar eclipses. I don't want to leave you with this really beautiful one where the this was again back to October 8th of 2014 at about or 5:00 in the morning.

00:09:44:16 - 00:10:31:13
Hope you enjoyed this video. If you did, please like it and subscribe to the channel because that helps me keep things going. So now I'm going to leave you with a moment of Zen.