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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Navigating the Night Sky

In this video, I talk about how we navigate our way around the sky. I talk about the constellations and a horizon-based coordinate system to find your way around the sky. I also describe the differences between an asterism, a common constellation, and the official IAU-designated constellations.

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 - 00:00:24:22
Hello, this is Jason Kendall, and I'd really like to welcome you to my introductory astronomy lectures. It's a wonderful journey to go out and start the hobby of amateur astronomy. And you'll always have a really wonderful time no matter what. Just going out and enjoying the night sky and. And seeing the stars and watching things move and watching things rise and set.

00:00:24:24 - 00:00:49:26
You don't have to have a telescope. You don't have to have a camera. You just have to have some time out as well. After dark. Find a dark place where you can see a lot of stars and just begin looking. That's the basics of observational astronomy. Get away from all the bright city lights as far as you can so that you can see pictures like this, which are the stars from Boulder, Colorado, that I took with a camera.

00:00:49:27 - 00:01:23:05
Well, this is actually a couple minute exposure, 60 second exposure with a DSLR camera And August 16th of 2017, about 11 p.m. from Boulder cut from the mountains above Boulder, Colorado. Boulder is the glow, sky glow off to the side there to the left. And we see some planes flying in our Boulder International Airport across the horizon. But what we do see, in addition to the tree in the foreground, in some people's houses, in the background, is we can see the Milky Way centered up rising up from the horizon.

00:01:23:05 - 00:01:49:12
That's that smoke. That's the Milky Way. Very often when people first see the Milky Way, they think it's smoke. Especially people who have lived in cities their entire life. They just can't believe it when they actually see the Milky Way in the sky in a very dark location. But if you also go outside on such a dark night and are able to find such a place that's hopefully nearby, you'll notice that you get lost trying to count the stars.

00:01:49:15 - 00:02:10:09
This image kind of tells that story where you could if you scanned around the sky, you would probably find that you'd see 2 to 4000 stars in a truly dark place. Most places in the URB are blighted by urban light pollution, but you can still find another places if you go hunting for them. And I suggest you try.

00:02:10:11 - 00:02:30:27
What we see here is stars in the sky and the Milky Way. Just to let you know behind the trees the teapot shape of Sagittarius. And off to the right, the bright star above, straight up from the hill. And it looks kind of reddish in between to start to bluish stars on either side. That enters the heart of the scorpion.

00:02:31:05 - 00:02:48:19
And the pinchers of the scorpion are almost to the edge of the screen, to the right. And in fact, if you look at the two lights that are really close together on the horizon, the two almost bright yellow lights, then if you look straight up from them, you see what looks like one of the brightest things in the sky.

00:02:48:21 - 00:03:08:25
That's not a plane. That's the planet Saturn in the constellation of Lucas between Sagittarius and Scorpius. When we look out in the night sky, we can certainly see quite a few things. Let's actually take a look. A new way of looking at how to find things. Because let's say I was outside with you and we were stargazing and seeing this.

00:03:09:02 - 00:03:31:18
How would I point out to you what Saturn is in the sky? We would have only two things to think about. How high is it off the horizon and where is it with respect to the horizon? And that is what we call the altitude and azimuth system. Now, we've clearly demarcate Saturn with this green bar and shown its altitude off the horizon.

00:03:31:18 - 00:04:00:00
Why does it go below those hills? Because it seems like the horizon should be the top of the sails. But it's not. It is actually not. Those top those hills. And I've marked due south. They're due north. Straight north is directly behind me. And let's not pretend that we can measure angles around. And so we can say, what is that angular measurement from the horizon and the green bar at the bottom to the green bar at the top that shows where Saturn is.

00:04:00:02 - 00:04:28:05
And how far around the horizon do we have to go from North through east, through south to that point from the left. So we could we can say, look at that altitude, bar the lower part and go left. That will get us to South and east and north. That will swing some angle all the way around. And that's roughly about 210 degrees around from due north, 180 degrees is of course due south, 90 degrees is due east.

00:04:28:11 - 00:04:52:27
So we're going a little bit west to south and it's 210 degrees Azimuth. And that bar, the green bar, is about 21 degrees altitude. And it just so happens that what on that date at that time in that location, Saturn had an azimuth of 210 degrees and altitude 21 degrees. And this is what we call the horizontal coordinate system.

00:04:52:29 - 00:05:17:25
And what I described was you find where north is and north is towards the north South Pole or Polaris, the North star. And then you simply face that on the horizon and slowly turn around, keeping your eyes level. And if you go 90 degrees, you'll be facing east and that'll have an azimuth angle of 90 degrees. And if you go all the way around such that azimuth angle is due south, you'll be facing away from north.

00:05:18:03 - 00:05:42:16
If you keep going a little bit around again to 210 degrees, you'll be at the azimuth angle we saw in the previous picture with Saturn at 210 degrees. Then we would have to go up in altitude off the horizon from the horizon to say that star. But in this case, it was the planet Saturn, 21 degrees. This looks like it's more than 45 degrees to that, that the altitude in this diagram.

00:05:42:22 - 00:06:03:03
And it's not even to east. So this looks like it, maybe 45 or 50 degrees azimuth and maybe 50 or 60 degrees altitude here in this in this diagram. And why do we have this coordinate system and what's with this dome sort of thing? And that's what we think of the sky. We think of the sky. We imagine the sky to be a dome over us.

00:06:03:06 - 00:06:25:23
And that is bound with a boundary of the horizon all around us. And that's our reasonable, normal way of with that we think of the sky that it overreaches us and that we're under some dark dome full of stars or a bright blue sky dome. And that's what we think of is as the celestial sphere or the sky.

00:06:25:25 - 00:06:46:26
Now, if you lie on your back as the observer and look straight up, that is the point in the sky is called the zenith. And there are many points on the horizon. There's a whole circle. The horizon is a circle around you is as the observer, the coordinates of altitude and azimuth make up what we call the horizontal or Altus system.

00:06:46:28 - 00:07:08:21
And it is dependent upon the exact date and time and location on earth that you are in order. That star will has different altitudes and different azimuth at different times and different dates at different places on the surface of the Earth. Why is that? Because the earth is a sphere and it's rotating and moving through space. So it's not the stars are not going to stay fixed.

00:07:08:24 - 00:07:32:15
That's right. And you see the sunrise, sunset. You've seen the moon rise and set. You see stars rise and set. So therefore they're constantly changing and azimuth and altitude. And if you were to call up a friend and you were in, say, Rhode Island and you were calling up a friend in California, who and it was very late at night, you were in Rhode Island an early eve in middle of early in the evening.

00:07:32:15 - 00:08:03:28
For the person in California, the same object in the sky would have a completely different azimuth and altitude, which would kind of make it difficult for you to explain where the thing is in the sky unless you have a different continents and stuff. But if we're out together in the star, gazing out on our back portrait, some dark location, we can always use the altitude and azimuth to help navigate around by and very because the stars and don't rise and set fast and things swinging around as fast as it could.

00:08:04:00 - 00:08:32:07
So that's very good. So when you're right next to each other. All right. Let's actually take a look now at the kinds of what we would do with these things. So we've got some stars in the sky. Maybe we want to say organize them. And so I've taken some snapshots from Stellarium and these and when we look closely at this, we see that there's a just a bunch of stars in the sky, but we can then group them in a particular ways called Constellations.

00:08:32:10 - 00:08:54:08
Constellations are areas of the sky with stars that form a particular pattern and any of these patterns, like you see the belt of Orion there, the V of Taurus and the well, the V of Taurus is in that isn't truly X, and neither is the training tiny, tiny little group of stars called the Pleiades up there in the upper right.

00:08:54:10 - 00:09:21:14
But definitely the box of Orion and the three stars of Orion. Those are accidental. All those stars are at very great distances and would look different if we orbited it at a thousand light years or so, as we are very distance in Orion today and we swan a thousand right light years around, it's the orientation of all these stars would change and we wouldn't see this familiar asterism known as Orion.

00:09:21:17 - 00:09:41:18
All constellations are accidental patterns that stars that because stars are different distances are not necessarily related to each other. They just happened include the Pleiades in the Hyades in here which are related to each other. And most of the patterns that that we describe and think of as constellations have been used for thousands of years and almost always are based on myths.

00:09:41:19 - 00:10:14:22
Some of the southern hemisphere, which are based on instruments, navigational instruments and such, were When we think about this, I just added the artwork of things that we might tell stories about the sky and the stories we might tell about the sky or okay, Orion is a great hunter and he's hunting Taurus the Bull, and he's backed up by the unicorn Monoceros and a the is dog in the lower left Sirius, the dog star Ursa Canis Major is chasing the rabbit at his feet.

00:10:14:25 - 00:10:45:09
There's all these kinds of little stories you can tell by a imagining that these gods and heroes and animals are up in the sky. And these are this mythology that we speak of in every culture has its own mythology across human history. It just so happens that the constellations they all describe to our internal actually agreed upon. And these particular constellations shown in this image are are mostly hailing from ancient Greece.

00:10:45:12 - 00:11:12:18
And Orion is a great hunter or warrior. But it's interesting in many sky cult, many cultures, very many cultures, irrespective of ancient Greece, but many cultures regard that pattern in the sky as a man or a warrior in the sky, which is really interesting. And it speaks to our ability to see shapes and things in our lot of our collective imagination as humans and what we think of and what are common things amongst all humanity.

00:11:12:18 - 00:11:46:22
That's kind of a fun thing to think about anyway. So now I'm going to do is I'm going to add the Constellation lines to help describe where now that we can trace out these things if we wish to my pointing them in the sky. In the sky, which these are a laser pointer or is it? No, a thousand years ago Internet laser pointers, maybe just somebody looking over your shoulder where you point your finger in the sky as you do stargazing and the constellation lying then would make up the image of that we see is this type of this artwork.

00:11:46:27 - 00:12:06:02
The artwork is not, of course, in the sky. You don't see that. You see the lines in the sky. None of this is in the sky. Only the stars and the Milky Way and the nebulae are in the sky. So we're all imagining these lines and we're all imagining this artwork in the in the lines. Then trace out the mythological artwork that we see here.

00:12:06:05 - 00:12:26:04
Now, the box that's around Orion, that is a particular kind of box by calling Asterism and the V of tourists, which looks like the tip of his horns and the eye of the bull, and that V looks like the head of the bull that in the end is advancing. He makes two other lines. I guess you can make out.

00:12:26:04 - 00:12:48:04
That's a good body. And one of those that's an asterism. It looks like the asterism of the horns of the bull typically asterisms are of bright, bright stars in the constellation. All right. So now we've added some names for some of these stars, some of these very famous names. Aldebaran is the name of the Eye of the Bull.

00:12:48:12 - 00:13:27:11
And we have Beetlejuice in the upper left shoulder of Orion. The right shoulder. Well, I mean, how is how last, as it were, we're looking at Orion, but from Orion's perspective, stage left, I guess. Stage right. But in to the left is Beetlejuice. And to the right is Bellatrix is other shoulder is split is named Rigel. The knee would be south and the belt stars have the names and attack on the lamb and talk up and they're all almost all the bright stars in the sky have names You can see Sirius in the lower left and Procyon and Canis Minor to the left of it in the middle, upper left.

00:13:27:13 - 00:13:53:21
I've removed the art so we can just show the lines and say, What? What are we suggesting to each other? And of course, these lines, again, are not actually in the sky. And either all these words and things, but what we do is we trace them out and we help people understand where stars are in the sky. We tell stories using the tracings that we might place and other that we guide other people, too, so we can associate them with the stories and mythology of the sky.

00:13:53:23 - 00:14:13:18
And it's fun to draw them out for a friend or to when you're in an evening stargazing session and say, okay, start from Bellatrix, alright? And you see this little arcs in the sky. That's the bottom. And if you look below, Bellatrix is three stars. That's like a belt. That's also like a belt. And there's the forehead hanging down and there's this two feet.

00:14:13:19 - 00:14:29:27
Rigel And then there's two shoulders. Bellatrix and Beetlejuice. This head is the three, two stars at the top, and he's got an upraised club the way up there. You know, you can make up all sorts of wonderful stories and you have to point the stars out to people. Otherwise they might not know which side you're talking about. So the lines help.

00:14:30:00 - 00:15:05:05
So today, though, constellations are much more clarified and constellations can be codified into these red lines. And those red lines were agreed upon by the International Astronomical Union a long time ago. And every star inside the box of those red lines that's on the sky, these are, again, real things. And they're just arbitrary demarcation on the sky so that we can say if we're looking at a star inside this box, that is that it's a it's a star in Orion.

00:15:05:08 - 00:15:25:08
So look up at the bow of Orion, and we see those two little stars that are above the rock, or at least a bunch of little dim stars above the bow. Those stars are also in the constellation Orion. They're just not associated with any of the lines or the mythology or the stories of Orion. And we look at the the horns of of tourists.

00:15:25:08 - 00:15:47:13
The Bull and Aldebaran is one of the bright stars of the of the the cluster, the Hyades cluster, a nearby star cluster. But all the other stars you see in that great box that surrounds the the Taurus. The Taurus is lines in Aldebaran and lines and off to the side, Pleiades, they're all part of the constellation Taurus as well.

00:15:47:15 - 00:16:09:19
These regions on the sky are now what we call the constellations, and they are agreed upon locations in the sky or regions in the sky, and there are 88 of them. And everyone in the world, every astronomer in the world, agrees that these are age and then helps us as scientists to understand the differences between all these locations in the sky.

00:16:09:22 - 00:16:29:02
All right. So now let's actually look at the concept of the Asterism and let's do this again and look at the concept of an ASTERISM And we've now we're looking at the constellation, the the asterism of the Big Dipper and the Big Dipper is, of course, off to the left there. And it looks like the familiar seven stars of the Big Dipper.

00:16:29:02 - 00:16:49:06
And if you don't know what you're looking for in there, they're the brightest seven stars in the lower left hand side and the Little Dipper is in the upper right. And the little dippers, a little tricky to see, but I'm going to highlight it in just a second. The Big Dipper is part of the constellation Ursa major, and the Little Dipper is part of the constellation Ursa minor.

00:16:49:09 - 00:17:08:06
And this is looking north on a late July night. So first what I'm going to do is I'm going to add the star names to the field of view and the star names themselves. You know, we have the seven me all of the bright stars in the Big Dipper have names as well as the three brightest stars in in the three.

00:17:08:06 - 00:17:28:14
The names of the three brightest stars in the Little Dipper also held. And there's Polaris. That's the North Star. It is not the brightest star in the sky. It just happens to be at the North Celestial Pole, which we'll get to shortly. Okay, so now what I'm going to do is I'm going to add the Asterisms to show you the locations in the sky that we call Asterism.

00:17:28:14 - 00:17:56:02
So the Little Dipper now is highlighted. We can see the stars, a Little Dipper, we can see the stars of the Big Dipper. There's also one a an uncommonly used asterism that pops up in psyllium called the mini Dipper, which is off to the side of the back in the in the Big Dipper. The big dipper is typically thought of as those seven stars and the mini dipper is almost never thought about in terms of in terms of the in terms of asterisms and thinking about.

00:17:56:03 - 00:18:19:28
So it's a very rare thing to see. Anyway, let's actually now go along and the constellation names, which are Ursa major and or some minor, Ursa minor is the full bear and Ursa major is the big bear. And those are Latin names. And now then I'm going to add their international astronomical Union constellation boundaries, which are those red lines we see in the sky.

00:18:20:00 - 00:18:45:03
And finally, I'm going to now add the constellation lines for the constellations themselves, and I'm going to zoom out to show a little bit more. The constellation lines that we see here in the sky are the common things. There's Draco, the Dragon Cetus Cassiopeia counterpart is notice the hunter is only two lines for Tennyson to teach in. Leo Minor.

00:18:45:06 - 00:19:05:19
A little lion has all that. So let's look at the various mythological artwork that's associated with these. And there we have the big Bear, Ursa major, which is a big bear. And the little bear is upside down going the other way. Draco is a dragon six as a seed and king. We see Perseus rising in the in the east.

00:19:05:22 - 00:19:27:14
And then we have the Arcturus, which is at the in the bottom of the foot, the type of of a Buddhist hunter. We have all these stories. There's the little there's a little lion. Leo Meyer And then we have a very, very, very busy sky, just a really busy sky with all of this artwork in this constellations and everything that we see.

00:19:27:20 - 00:19:46:02
So I'm going to clean things up and just reduce it all the way down to what we see in the sky. We might want to point out to somebody what it looks like on a night sky and that's our constellations that we think of that we might draw out to a friend or a companion under a stargazing section.

00:19:46:04 - 00:20:11:08
But really, none of that's there. And all we really get is this night sky. And hopefully we know the cardinal directions to end for north and then the northwest and we see that Polaris was the star that's directly above the horizon. We can always find true North by looking for Polaris in the little Dipper and then swinging east from there to get our azimuth angle.

00:20:11:14 - 00:20:31:09
And our altitude of all of the Little Dipper will show us our latitude. I already said that. keep going. All right, So this is just a wonderful thing that we see as we go through the night sky. And you got to hopefully get to see something beautiful like this. This isn't a this is these are new things.

00:20:31:09 - 00:21:05:01
And so this is a hand-colored engraving of Ursa major by John Beyer. John Johann Bayer, which appeared in the Year that You're an American in 1603, very close to the time that Kepler and and Galileo were and were doing their work on the night sky. These pictures in the sky of the various and sundry creatures are different. And you can see Johann Bayer's image of of Ursa major makes it the tail is the three stars and the body is basically very little of it.

00:21:05:03 - 00:21:26:05
But the contents, the Big Dipper is only the latter is the haunches of the Big Bear. And we have all these other stars that are bright in the sky that we point out to find the constellation. And it were pictures like these that help that people try to understand locations in the sky and to map the sky mythology that people had been discussing for a long time.

00:21:26:07 - 00:21:49:18
Those briefly look at the overview for this long. And what we have is this is a free software stellarium again, and this is a night sky simulator and you can see the settings across the bottom. And we're looking south at this point. Again, I'm going to try to show the sky from Boulder where I took that picture of now it's just mid-August in 2023 as opposed to that.

00:21:49:18 - 00:22:21:08
So we're missing Saturn from this field of view. And we're also, again, facing south by Southwest. And as you can see by the cardinal based directions across the horizon there. So we've added the constellation lines. As you can see, and that traces the common asterism. That's the core of each constellation. And the Scorpius has the three prongs and the heart of the scorpion is is is this raging heart and there's a teapot for Sagittarius, and that's the asterism for those constellations.

00:22:21:11 - 00:22:47:06
So now I'm going to go on and add in the names of the constellations are Sagittarius and Scorpius called Australis. And we're also now going to start using a tool that'll show the angular separation from stars from the horizon. And what we're actually using is trying to see, well, how high off the horizon is a given star in in Sagittarius.

00:22:47:06 - 00:23:07:05
And so that particular star in Sagittarius has an altitude of approximate 20 degrees and then we're going to look at other stars, too, just to see that in order to move around. I'm going to try. So I'm going to click on this individual star and that star is going to be see this one new key, which is also in Sagittarius.

00:23:07:12 - 00:23:52:14
And I'm going to try getting the angular height of the horizon of that particular thing. And I've got a kind of seen around just so so it's going straight up from the horizon and we can see it's approximately almost 23 degrees and you can see that it has an azimuth angle, see the numbers way up in the left hand corner of approximately 192 degrees or just under 192 degrees means that we need to turn 192 degrees east from north to get to the horizon point directly below that star again, we had the turn 192 degrees east from north around the horizon to get to the point directly below that star on the horizon.

00:23:52:17 - 00:24:34:07
Then we go up 20, roughly 23 degrees in order to get to that star horizon. Now let's set the constellation boundaries in after we've done all this, because you know, why not do that? And because that's always fun to have those in and see you there. They are a completely important now when you turn on the altitude and azimuth grid and this is what we think of when we go outside and we're making believe that there's this dome over our head and we're using these grid lines in order to get us to help us navigate the sky in this altitude and azimuth system.

00:24:34:09 - 00:24:59:27
So each of the green lines is separated by five degrees on the grid and notice all distorted squares. Notice that each of the vertical lines comes straight up from the horizon. And now they seem to kind of bend and curve as we move around. But they all, if you face that direction, the exact direction, the line that you are facing is coming directly from the horizon.

00:24:59:27 - 00:25:22:12
And it is 90 degrees from either direction on the horizon. So every one of those azimuth lines that comes up from the horizon is 90 degrees from the horizon. All of the lines going across are parallel to the horizon going up. So it's kind of funny looking because it's like, wait a second, the horizon is kind of flat at the bottom and it curves going up.

00:25:22:12 - 00:25:51:25
It's like, yeah, because it's a we we project a dome on the sky, but all of those altitude lines are parallel to the horizon, and all of the azimuth lines come 90 degrees straight up from the horizon towards the zenith. And that trick of projection is all there, spherical trigonometry for you. So now then, let's swing around to the south and show off.

00:25:51:28 - 00:26:21:04
Let's try to show off the altitude and the azimuth of some of these lines just to prove it. I mean, we see the lines off to the side, 25 and so forth and 10 to 20. But let's actually just go through and take that angle. Okay, Here we go all the way over here. Yep. And now I'm going to look at that star or actually this line I'm going to drag from that line all the way down to the horizon, assuring that I have equidistant between those two azimuth angles.

00:26:21:04 - 00:26:45:12
And we get those lines. And sure enough, it's that 120 and this one's a 35. And so we're pretty confident that we'll. Okay, now we're going to swing around the horizon like we're standing in place, keeping our head level and just turning around to face roughly north ish. And we kind of swing around with too far going east, and then we're going to look right out there as a Big dipper.

00:26:45:12 - 00:27:06:26
Again, we just we're talking about that and swinging around. There's Perseus. We're talking about that, too. And we can swing all the way around back down to the south again. And we see that the altitudes are the altitude lines are in parallel horizon. Now, I'm going to widen the field of view. So I zoomed it out. So it's about 150 degrees field of view, and that is how all the lines converge at the top.

00:27:07:03 - 00:27:33:00
That's the zenith. That's where all the azimuth lines converge. And we see that Altair in Aquila is about 58 degrees up from the horizon at this date and on this time at this location. And Vega is all the way over there. Our 58 180 degrees, roughly. Azimuth and Lira is approximately 270 degrees Azimuth and 6078 degrees off and rising.

00:27:33:02 - 00:27:54:08
But we can't go straight down in our field of view. We have to go straight down towards the horizon. The nearest point that Lyra is to the horizon. So we have to swing around and bring that all the way down. Let's say pulled their arms to the right because we have to go straight down to the horizon such that the altitude is 90 degrees up from the horizon.

00:27:54:08 - 00:28:29:07
Either way, the only way to properly measure where Lyra was is along the horizon. So let's try to measure the angle on the sky of something that's an altitude line that's not directly on the horizon like this. And we notice that we're not quite getting lined up with those things because this is the shortest angle between these two points on the sky, which is not in a one of the altitude lines.

00:28:29:10 - 00:28:53:06
Those altitude lines are parallel to the horizon. That's not the shortest angular separation between these two things, which the measuring tool is trying to show. Okay, so now we can go over to Hammoud in Paris, and it has an azimuth angle, about 68 degrees, as you can see from the stats. Nevertheless. But if I naively measure the angle of the sky to the innocent angle to north again, it is too low by a few degrees.

00:28:53:08 - 00:29:15:12
And that's because of that. We have to measure across the horizon. And when we do finally do measure across their eyes into it there our 68 degrees. Right? So that's what we see now, the analysis. And now we're going to go take a look and zoom in. I wonder I zoom in on the zenith. So let's go try to look at some stars at the zenith.

00:29:15:14 - 00:29:37:04
But we can look first and say, where's the zenith that day? All the way up there. It's like we can go all the way up. And there's the zenith at approximately 90 degrees. So it's not a great measurement. So it's actually just going to click on some stars and zoom in. There we go and often go so we can see that we got to move it around a little bit, get all summed up nicely, right?

00:29:37:08 - 00:30:10:20
So if we go over the top, so we looking straight overhead now we're on our backs, looking straight up, trying to orient ourselves and see what stars are at the zenith of the stars change minute by minute, hour by hour. Now I'm going to zoom out and take in a full field of view. This is the whole sky in a circular projection and you'd never see this when you lie on your back in your peripheral view always extends to the horizon, always to your left, in your right and above and down when you're lying on your back.

00:30:10:22 - 00:30:36:07
So we don't see this unless you have extraordinary, really bad tunnel vision and macular degeneration or some sort of eye disease. But I don't know if is possible with with such tunnel vision, digital degenerative diseases, but maybe this but what's interesting about this particular projection is it shows everything that's in the sky at the same time. And that's kind of nice because it's hard to see all the sky once.

00:30:36:09 - 00:31:01:02
So this looks like just a map of everything that's in the sky on at Boulder, Colorado, on August 12th of 2023. Right. That was what was in the sky at that time, at that place. So that's pretty helpful. It helps us to make a map of what's in the sky. So now I'm going to try some things and try and maneuvering this around a bit.

00:31:01:02 - 00:31:15:16
You know, maybe I can oriented better, but you can see that as you turn around, you're facing different directions. Maybe you're facing to north. It's hard to make the same case. Absolutely true. North For now, I'm going to do this. I'm going to start skipping forward week by week. You can see the numbers go across in the bottom, right.

00:31:15:18 - 00:31:38:27
But I'm staying keeping the time fixed at 11:20 p.m. local time. And each of these is a snapshot which repeats year after year in the same location on Earth. So they keep going forward and forward and forward. Now, in 2024 or 2025, we can see that these patterns recur and recur. The only things that are going to be different are what's on the zenith at different days.

00:31:38:29 - 00:32:03:29
So the stars change, which ones are at the top of the zenith at different, different days. And now we're going to kind of go back and zoom out and face due north for just a second. And there's our familiar earth, some minor again. Now I'm deliberately showing a slight or some minor for a reason. Let's actually speed forward in time, just like I was doing.

00:32:03:29 - 00:32:25:24
And I'm going when we get a time. And as I do so, you see that the stars seem to rotate around that one star Polaris in very some minor. That's the pole star. So we'll talk about that in another video on the celestial sphere. So let's just go back and take another look. This is one of those maps that we're talking about.

00:32:25:26 - 00:32:47:26
If we look at the night sky in October, this was so night sky that JPL, that NASA, you can certainly go there and download these things from them. This is free to download and it's a good little map. It shows you the biggest asterisms of the night sky. You can see that they highlight the Big Dipper. The key is to highlight Cygnus the Swan.

00:32:47:28 - 00:33:11:24
They highlight the great square of Pegasus and they also show, my goodness, there's a teapot in Sagittarius two that we talked about and the moon, where it is and where Jupiter is, and Saturn is in the sky. And of course the planets will move with respect to the background stars, But this kind of map will show you will help you understand the things in the sky that you see when you go out just to go stargazing.

00:33:11:26 - 00:33:34:09
And then you can either look at a more detailed map to get more detailed versions of these constellations and learn more of the constellation names here in the sky. Or you can just have fun trying to find these and take this out with you at about 9 p.m. or in late October, about eight. It'll change a little bit as time goes on and things will rotate around the sky as we saw.

00:33:34:12 - 00:33:55:24
But that's that's kind of what we're trying to help you do, is go outside of the night sky and have a proper little map like this and find the things that are there that this time we were just talking about the altitude, the asthma, what the definition of zenith is, the horizon that constellations are the collections of stars bright and dim.

00:33:55:24 - 00:34:19:27
That can be part of some pattern or not, but don't now, eight one of eight regions on the sky declared internationally by the International Astronomical Union that all astronomers and scientists use across the Earth. And the asterisms that we see in this thing are helpful little things to help us navigate in nice and wonderful evening stargazing.