1 00:00:02,740 --> 00:00:06,693 Today we are going to start our class. And, the best way to start a class on 2 00:00:06,693 --> 00:00:11,140 astronomy is to just go outside and take a look at the night sky see some of the 3 00:00:11,140 --> 00:00:15,697 objects we are going to talk about in their actual natural habitat so to speak. 4 00:00:15,697 --> 00:00:20,034 There's far too many of us to fit in one place and we are scattered too widely 5 00:00:20,034 --> 00:00:24,591 over the globe but through the wonders of technology I am going to invite you in a 6 00:00:24,591 --> 00:00:28,791 minute to do a virtual night sky tour with me and I encourage all of you to 7 00:00:28,791 --> 00:00:34,084 take either a virtual tour or even better if you can, to go outside and take a look 8 00:00:34,084 --> 00:00:39,506 up at the sky familiarity with the night sky is not the main object of this class, 9 00:00:39,506 --> 00:00:43,587 but it's a very pleasant side effect and I hope you'll enjoy it. 10 00:00:43,587 --> 00:00:48,180 So without further ado let me invite you to join me virtually in a. 11 00:00:48,180 --> 00:00:50,769 Field outside of Athens, Greece for definiteness. 12 00:00:50,769 --> 00:00:54,060 And we'll look up and see some of what we can see in the sky. 13 00:00:54,060 --> 00:00:58,327 Welcome to our observatory. We've chosen to locate ourselves in the 14 00:00:58,327 --> 00:01:02,722 outskirts of Athens, Greece. It is November 27th at 9 p.m. 15 00:01:02,722 --> 00:01:07,691 And when our software is simulating the sky and we're looking to the south, we 16 00:01:07,691 --> 00:01:11,130 have a very broad field of view of a full 180 degrees. 17 00:01:11,130 --> 00:01:15,524 So we can see all the way from the. Eastern horizon to our left to the 18 00:01:15,524 --> 00:01:20,718 western horizon to our right, but because of the light pollution of a nearby city 19 00:01:20,718 --> 00:01:25,171 we see very few stars in the sky. This might be what you can see or it's 20 00:01:25,171 --> 00:01:28,015 certainly what I can see when I step outdoors. 21 00:01:28,015 --> 00:01:33,581 but the brightest stars in the sky are bright enough to shine against the glow. 22 00:01:33,581 --> 00:01:37,230 So we might see over here in the east Betelgeuse and Rigel. 23 00:01:37,230 --> 00:01:42,804 And perhaps Capella and Aldebaran. And over here on the western horizon, 24 00:01:42,804 --> 00:01:47,986 we'd see three very bright stars. Vega over here, Altair down there. 25 00:01:47,986 --> 00:01:53,953 And, Deneb over here, and these make up what is normally called the summer 26 00:01:53,953 --> 00:01:58,236 triangle. Let's step a little farther away from the 27 00:01:58,236 --> 00:02:02,280 city where more stars are visible, and try to get a better look. 28 00:02:03,460 --> 00:02:08,563 There, that's better with software it's much easier to turn off light pollution 29 00:02:08,563 --> 00:02:12,698 than it is in real life. And now we see the same view of the sky 30 00:02:12,698 --> 00:02:16,898 as it must have appeared before the advention of electric lights. 31 00:02:16,898 --> 00:02:20,839 And let's take a look and name some of the objects we see. 32 00:02:20,839 --> 00:02:26,007 over here, to the east we saw the two bright stars Betelgeuse and Rigel, which 33 00:02:26,007 --> 00:02:29,400 are now shown to be. Seen to be part of the famous 34 00:02:29,400 --> 00:02:34,580 constellation of Orion the hunter, there's his chest and his legs, his belt 35 00:02:34,580 --> 00:02:39,830 from which hangs his dagger, his club or bow over here, his outstretched arm. 36 00:02:39,830 --> 00:02:45,220 He even has a head up there and that would be Orion the hunter and Aldebaran 37 00:02:45,220 --> 00:02:50,400 will be part of Taurus the bull. There's his head and his body and there's 38 00:02:50,400 --> 00:02:54,810 long outstretched horns. looking further to the right we can 39 00:02:54,810 --> 00:02:59,150 identify some other famous groups there's W shaped objectives. 40 00:02:59,150 --> 00:03:03,096 associated with Cassiopeia, the vain queen. 41 00:03:03,096 --> 00:03:06,891 And not far from her, this great square of Pegasus. 42 00:03:06,891 --> 00:03:10,914 And from the great square Pegasus, towards Cassiopeia. 43 00:03:10,914 --> 00:03:16,606 These two streaming lines of stars, associated to Andromeda, Cassiopeia's 44 00:03:16,606 --> 00:03:20,923 daughter. And up here Vega, the bright star we saw 45 00:03:20,923 --> 00:03:25,316 in the western sky is part, in fact, of Orpheo's lyre. 46 00:03:25,316 --> 00:03:28,950 This is the constellation Lyra. And finally, 47 00:03:28,950 --> 00:03:32,612 my favorite constellation we talked about Deneb over here. 48 00:03:32,612 --> 00:03:35,516 And Deneb is just the tail of Signus the swan. 49 00:03:35,516 --> 00:03:40,378 There's his tail and severed his heart, and a long swan neck that ends at 50 00:03:40,378 --> 00:03:44,041 Albireo, his head. And his pretty swept back swan wings, you 51 00:03:44,041 --> 00:03:48,461 can certainly see a swan. There are many other constellations but I 52 00:03:48,461 --> 00:03:53,070 don't have time to show them all. Let's allow the software to do that for 53 00:03:53,070 --> 00:03:58,567 us. Here that the software designate for us 54 00:03:58,567 --> 00:04:01,119 the. most famous of the constellations. 55 00:04:01,119 --> 00:04:05,243 And the brightest stars that comprise the shape or the asterism of the 56 00:04:05,243 --> 00:04:08,321 constellation. And we see Orion the hunter, and Taurus 57 00:04:08,321 --> 00:04:11,110 the bull, and Pegasus, the flying horse, and so on. 58 00:04:11,110 --> 00:04:14,653 As well as many others. And what we recognize is that many of 59 00:04:14,653 --> 00:04:18,545 them have their origin in Greek mythology, at least in the northern 60 00:04:18,545 --> 00:04:20,520 hemisphere. The reason for this is, 61 00:04:20,520 --> 00:04:24,744 and the point I'm trying to make with this image is, that if you show this 62 00:04:24,744 --> 00:04:29,312 picture without the helpful blue lines, to someone who lived in Athens thousands 63 00:04:29,312 --> 00:04:32,280 of years ago. I don't know, the philosopher Aristotle, 64 00:04:32,280 --> 00:04:36,848 he would not only recognize the stars, he would name the constellations and he'd 65 00:04:36,848 --> 00:04:41,668 use the same names that we use, because the pattern of the sky as Aristotle saw 66 00:04:41,668 --> 00:04:46,781 it on a fall day in Athens 2000 years ago would be extraordinarily similar, 67 00:04:46,781 --> 00:04:51,280 essentially identical to what we see today, absent light pollution. 68 00:04:51,280 --> 00:04:54,262 There is this beautiful permanence in the sky. 69 00:04:54,262 --> 00:04:58,865 The stars that we see today are essentially the same as they've always 70 00:04:58,865 --> 00:05:01,717 been. And this is something that has made 71 00:05:01,717 --> 00:05:06,321 astronomy one of the oldest sciences. It's also something we can use to 72 00:05:06,321 --> 00:05:10,988 establish a geography of the sky, so that, if I want to describe, or if an 73 00:05:10,988 --> 00:05:16,434 astronomer wants to describe viewing an object that lies right here, even if it's 74 00:05:16,434 --> 00:05:20,843 not part of the asterism of Orion, he would say, the star lies in the 75 00:05:20,843 --> 00:05:26,741 constellation Orion. Astronomers have formalized this by in 76 00:05:26,741 --> 00:05:30,877 recent memory actually dividing the sky into 88 regions. 77 00:05:30,877 --> 00:05:35,751 In the Northern hemisphere they're associated to ancient Greek 78 00:05:35,751 --> 00:05:41,660 constellations for the most part, and so now we precisely can distinguish a star 79 00:05:41,660 --> 00:05:47,494 that lies in the constellation Orion from some nearby star that lies in Taurus. 80 00:05:47,494 --> 00:05:53,329 And when we talk about stars lying in one constellation or the other I will be 81 00:05:53,329 --> 00:05:58,325 referring to this the treaty, that divides the sky into the 82 00:05:58,325 --> 00:06:02,851 88 constellations up, the point that this again is trying to 83 00:06:02,851 --> 00:06:08,233 remind us of is that, a star that is in Orion now will be in Orion a century 84 00:06:08,233 --> 00:06:14,181 hence, and so there's this geography that we set up and we can identify positions 85 00:06:14,181 --> 00:06:20,170 in the sky. Removing for a moment all the distracting 86 00:06:20,170 --> 00:06:24,750 lines that the software was drawing, let's take a closer look at some of the 87 00:06:24,750 --> 00:06:29,330 objects we're seeing and try to pay attention again to what we're seeing. 88 00:06:29,330 --> 00:06:33,669 So we see large numbers of stars. We noticed that they were different 89 00:06:33,669 --> 00:06:36,139 colors. Some of them were more reddish or 90 00:06:36,139 --> 00:06:40,983 orange-ish or yellow and some are blue. The colors of stars are in themselves an 91 00:06:40,983 --> 00:06:43,415 interesting topic. We'll talk about that. 92 00:06:43,415 --> 00:06:48,402 the distribution of stars is interesting. If you look, you'll see that there are 93 00:06:48,402 --> 00:06:52,537 less stars here or here than there are along this region of the sky. 94 00:06:52,537 --> 00:06:57,341 This stripe through the sky and in fact, if we look closely, we'll see that even 95 00:06:57,341 --> 00:07:01,294 in between the stars the sky here is brighter than elsewhere. 96 00:07:01,294 --> 00:07:04,517 This is, of course, the famous stripe of the milky way. 97 00:07:04,517 --> 00:07:09,289 We'll want to take a close look at that. Here's what part of the Milky Way looks 98 00:07:09,289 --> 00:07:12,214 when you take a slightly long exposure photograph. 99 00:07:12,214 --> 00:07:16,953 The exposure brings out many, many stars an we see that this bright stripe in the 100 00:07:16,953 --> 00:07:20,346 sky that I call the Milky Way. has a lot more structure. 101 00:07:20,346 --> 00:07:24,499 It's not just a white stripe. There are these darker areas and brighter 102 00:07:24,499 --> 00:07:26,664 areas. Different colors, lots of stars. 103 00:07:26,664 --> 00:07:31,110 We'll take a close look at that and try to understand what the Milky Way is. 104 00:07:31,110 --> 00:07:36,419 There are some other objects visible in the sky that will justify a closer look 105 00:07:36,419 --> 00:07:41,280 of the form that Aristotle would not have been able to take advantage of. 106 00:07:41,280 --> 00:07:46,717 if we look at Orion here, and if we look at the stars, the three stars that form 107 00:07:46,717 --> 00:07:51,962 the dagger dangling from Orion's belt, then suddenly the middle one it's pretty 108 00:07:51,962 --> 00:07:56,632 clear, does not really look right. There's something fuzzy about that star. 109 00:07:56,632 --> 00:08:00,470 we'll take out a telescope and get a closer look at that. 110 00:08:00,470 --> 00:08:05,934 The slightly fuzzy suspicious star in the center of Orion's dagger that we 111 00:08:05,934 --> 00:08:11,253 mentioned turns out in a moderate telescope to be a lot more interesting 112 00:08:11,253 --> 00:08:15,407 than you'll think. In fact all of this stuff all of these 113 00:08:15,407 --> 00:08:21,090 stars all of this nebulous scattered light blue and pink these darker regions 114 00:08:21,090 --> 00:08:25,389 all of this is what our eyes sees as a slightly fuzzy star. 115 00:08:25,389 --> 00:08:31,218 And, understanding what is going on in the Orion nebula is going to be something 116 00:08:31,218 --> 00:08:36,217 that'll be very exciting for us. Slightly farther south, over here, just 117 00:08:36,217 --> 00:08:41,272 past Taurus, and in the constellation Taurus in particular, is this wierd 118 00:08:41,272 --> 00:08:45,624 collection of stars. A whole bunch of stars clustered together 119 00:08:45,624 --> 00:08:49,204 very close. The collection of seven bright stars in 120 00:08:49,204 --> 00:08:53,343 the constellation Taurus. Traditionally called the Pleiades, in 121 00:08:53,343 --> 00:08:55,405 some cultures. The Seven Sisters. 122 00:08:55,405 --> 00:08:59,271 different names for this obvious bright collection. 123 00:08:59,271 --> 00:09:03,845 Here are the seven bright stars. We see that there are many others near 124 00:09:03,845 --> 00:09:06,551 them, just not bright enough for us to see. 125 00:09:06,551 --> 00:09:11,448 And, even again, as in Orion we see that there is this nebulous stuff, there's 126 00:09:11,448 --> 00:09:15,636 this blue shiny stuff that is not a star, that is producing light. 127 00:09:15,636 --> 00:09:19,760 So some of the light we see is not coming from the stars at all. 128 00:09:19,760 --> 00:09:25,412 And if we look at this collection of stars, then perhaps it's worth looking, 129 00:09:25,412 --> 00:09:30,485 just below Pegasus over here. If we looked very closely, there would be 130 00:09:30,485 --> 00:09:35,703 a faint and slightly fuzzy object, probably better seen with a telescope 131 00:09:35,703 --> 00:09:39,747 than the naked eye. In a moderate telescope, the group, 132 00:09:39,747 --> 00:09:45,082 slightly faint, fuzzy object in the constellation Pegasus that I mentioned 133 00:09:45,082 --> 00:09:49,017 turns out to be this beautiful, globular cluster called M13. 134 00:09:49,017 --> 00:09:54,019 again we see many, many, many stars, far more in fact than in the Pleiades. 135 00:09:54,019 --> 00:09:59,487 We also see that they're all dimmer the stars in the Pleiades were bright like 136 00:09:59,487 --> 00:10:02,422 this. These are dimmer objects, and they also 137 00:10:02,422 --> 00:10:05,490 appear to be very much more tightly clustered. 138 00:10:05,490 --> 00:10:09,730 In a constellation of Andromeda up here in between 139 00:10:09,730 --> 00:10:13,841 Pegasus and Cassiopeia. If we look around here, there's another 140 00:10:13,841 --> 00:10:17,820 one of those fuzzy objects. Suspiciously, not quite starlight. 141 00:10:17,820 --> 00:10:22,635 If you magnify it a little bit and collect light for a long time and process 142 00:10:22,635 --> 00:10:27,014 carefully, turns out to be this beautiful, richly structured object, the 143 00:10:27,014 --> 00:10:31,267 great spiral galaxy Andromeda. I should point out that the fuzziness 144 00:10:31,267 --> 00:10:34,707 that we see, is only the brightest central part of this. 145 00:10:34,707 --> 00:10:39,460 This object itself is about five times the size of the full moon in the sky. 146 00:10:39,460 --> 00:10:44,339 It's very large and very, very faint, and requires careful image processing and 147 00:10:44,339 --> 00:10:47,331 light collection to get all this structure out. 148 00:10:47,331 --> 00:10:51,589 But nevertheless, our eyes without misleading us, there's something 149 00:10:51,589 --> 00:10:54,686 interesting there certainly worth investigating. 150 00:10:54,686 --> 00:10:59,259 Farther to the west. Remember the bright star Vega in the 151 00:10:59,259 --> 00:11:04,186 constellation Lyra. If you look over here in Lyra, we'll see 152 00:11:04,186 --> 00:11:10,365 with a telescope a faint fuzzy object. The slightly fuzzy object in the 153 00:11:10,365 --> 00:11:17,129 constellation Lyra that we saw, with a moderate telescope turns out to be this 154 00:11:17,129 --> 00:11:22,761 beautiful ring shaped, nebulous light. lots of fun colors in this and 155 00:11:22,761 --> 00:11:28,426 understanding what this ring structures is will be a lot of fun for us as we go 156 00:11:28,426 --> 00:11:31,390 along. And finally, we'll take a close look at 157 00:11:31,390 --> 00:11:35,605 this moderately bright star Albireo, the head of Cygnus the Swan. 158 00:11:35,605 --> 00:11:40,677 when you look at it more closely, turns out to be not one but two stars of 159 00:11:40,677 --> 00:11:45,683 differing brightnesses, there's a bright and a dimmer star, and of completely 160 00:11:45,683 --> 00:11:49,371 different colors. One of these is orange, the other is 161 00:11:49,371 --> 00:11:52,270 described by various people as being either. 162 00:11:52,270 --> 00:11:56,161 Purple or blue or green, but certainly these two stars are very obviously 163 00:11:56,161 --> 00:11:59,359 different colours. Understanding why stars come in different 164 00:11:59,359 --> 00:12:03,517 colours, what these two have to do with each other, will be another topic we'll 165 00:12:03,517 --> 00:12:06,696 spend some time on. Hope you enjoyed the little preview of 166 00:12:06,696 --> 00:12:11,308 all the things that we can see that poor Aristotle could not because he did not 167 00:12:11,308 --> 00:12:14,030 have telescopes. Let's go back to what it is that 168 00:12:14,030 --> 00:12:17,364 Aristotle did see. I've made a big deal of the fact that the 169 00:12:17,364 --> 00:12:20,475 sky is unchanging. But in a sense I was cheating all the 170 00:12:20,475 --> 00:12:23,865 time we've been talking it's still 9 p.m. in our simulation. 171 00:12:23,865 --> 00:12:27,809 I'm now going to let time move at a somewhat accelerated pace and then we 172 00:12:27,809 --> 00:12:30,699 will see. That the sky is not in fact unchanging, 173 00:12:30,699 --> 00:12:34,435 things move. Orion is clearly moving from low in the 174 00:12:34,435 --> 00:12:39,152 eastern horizon, to high in the south and eventually will set in the west, But 175 00:12:39,152 --> 00:12:43,624 things maintain their shape, the motion is not random, the motion is rigid. 176 00:12:43,624 --> 00:12:48,280 Of course pretty soon, the sun will rise and we might as well stop observing. 177 00:12:48,280 --> 00:12:54,102 So let's collect ourselves after a good hot cup of strong Greek coffee, and 178 00:12:54,102 --> 00:12:59,403 summarize what it is we've learned. Back from our night under the stars, 179 00:12:59,403 --> 00:13:04,308 hopefully all energized and excited to understand all the things that we've 180 00:13:04,308 --> 00:13:07,665 looked at. Let's see what it is that I was trying to 181 00:13:07,665 --> 00:13:12,570 make clear from these observations. we saw that we see many, many stars. 182 00:13:12,570 --> 00:13:16,120 We can see as many as 3,000 at a time on a clear night. 183 00:13:16,120 --> 00:13:21,412 And we saw that we named the groupings by ancient Greek names because the pattern 184 00:13:21,412 --> 00:13:26,124 that we see in the sky is unchanging. We also watched the sky move, but we 185 00:13:26,124 --> 00:13:28,900 noticed that the motion was a rigid motion. 186 00:13:28,900 --> 00:13:32,057 Betelgeuse and Rigel remain in the same relative position. 187 00:13:32,057 --> 00:13:36,084 They're both in Orion in the same relative position throughout the motion 188 00:13:36,084 --> 00:13:38,316 of the sky. And in fact they have been in that 189 00:13:38,316 --> 00:13:40,766 position since humans started observing them. 190 00:13:40,766 --> 00:13:45,229 So we can set up a geography of the sky. We can declare some part of the sky to be 191 00:13:45,229 --> 00:13:47,787 Orion, and another part of the sky to be Cygnus. 192 00:13:47,787 --> 00:13:51,870 And this is a meaningful thing despite or throughout the motion of the sky. 193 00:13:51,870 --> 00:13:55,859 that said, the sky moves. Everything rises in the east and sets in 194 00:13:55,859 --> 00:13:58,733 the west. So what you see in the sky at any given 195 00:13:58,733 --> 00:14:02,839 time is not of constant time. And our job for the rest of this week is 196 00:14:02,839 --> 00:14:07,004 going to be to understand and mathematically describe, at some level of 197 00:14:07,004 --> 00:14:11,287 precision, this motion and this permanence and how we can predict what it 198 00:14:11,287 --> 00:14:14,513 is that we will see, looking up from Athens at 9 p.m. 199 00:14:14,513 --> 00:14:16,215 in what direction in the sky.