1 00:00:00,800 --> 00:00:05,457 Hey, so, we spent a week looking at main sequence 2 00:00:05,457 --> 00:00:10,484 stars and we can apply really fun and exciting thinking and observation to 3 00:00:10,484 --> 00:00:13,581 learn a lot about them. That's 90% of the stars. 4 00:00:13,581 --> 00:00:18,967 We want to know about the others and one of the things that main sequence stars 5 00:00:18,967 --> 00:00:22,441 taughts us is that they're not eternal, they burn out. 6 00:00:22,441 --> 00:00:27,210 So if we see any they must be forming, if we can ask what happened where they came 7 00:00:27,210 --> 00:00:31,639 from, how it is that they formed, and what happens when they are no longer able 8 00:00:31,639 --> 00:00:35,217 to be main sequence stars. What happens to a star when its done, 9 00:00:35,217 --> 00:00:38,170 that'll be the topic of this week stellar evolution. 10 00:00:38,170 --> 00:00:43,699 The challenge that faces us when trying to understand star evolution is that 11 00:00:43,699 --> 00:00:48,797 stars evolve, but very slowly. The time scale for the sun's evolution is 12 00:00:48,797 --> 00:00:53,320 tens of billions of years. We do not get to watch a star evolve. 13 00:00:53,320 --> 00:00:58,778 we get a snapshot of the universe as it is now, and so we will need, again, to 14 00:00:58,778 --> 00:01:04,594 apply both painstaking observation and modeling and understanding of the science 15 00:01:04,594 --> 00:01:08,400 to pick piece together a picture of how stars evolve. 16 00:01:08,400 --> 00:01:13,174 I spoke about sort of population studies as the realm of sociologists, I think 17 00:01:13,174 --> 00:01:16,440 last week. probably a better analogy is the one I 18 00:01:16,440 --> 00:01:21,340 quoted on the title slide due to the famous British astronomer Sir William 19 00:01:21,340 --> 00:01:24,293 Herschel, who liken an astronomer to someone 20 00:01:24,293 --> 00:01:29,318 wandering through a beautiful garden and trying to understand by looking at the 21 00:01:29,318 --> 00:01:34,470 plants, how it is that they developed and evolved and developed and grow and 22 00:01:34,470 --> 00:01:42,969 you can relate if you wish the fully grown redwood to a sapling, even though, 23 00:01:42,969 --> 00:01:48,685 no living biologist has seen a the redwood sapling grow into a 4,000 24 00:01:48,685 --> 00:01:52,868 year old mature tree. We know enough about the way plants work 25 00:01:52,868 --> 00:01:56,730 to relate the two. And we have to learn enough about the way 26 00:01:56,730 --> 00:02:00,446 stars work to make the same observations about stars. 27 00:02:00,446 --> 00:02:04,950 one of the laboratories that we have to do this is star clusters. 28 00:02:04,950 --> 00:02:09,190 Clusters are, remember, are formed when a cloud starts collapsing. 29 00:02:09,190 --> 00:02:13,496 That means all of the stars in a cluster formed at the same time, 30 00:02:13,496 --> 00:02:18,796 comparing the snapshot that different clusters give us at different times since 31 00:02:18,796 --> 00:02:24,072 they were created allows us to compare what the status is of different stars. 32 00:02:24,072 --> 00:02:28,905 All the different stars in a cluster, when they are the same age and this gives 33 00:02:28,905 --> 00:02:33,739 us different snapshots of the population and this will be an important tool in 34 00:02:33,739 --> 00:02:36,859 understanding what we know about star evolution. 35 00:02:36,859 --> 00:02:41,449 So the plan for the week is start by talking about how stars form. 36 00:02:41,449 --> 00:02:45,170 We'll talk about the pre-main sequence aspect of solar evolution. 37 00:02:45,170 --> 00:02:49,635 We'll skip over the rather boring sedate main sequence and talk about all the 38 00:02:49,635 --> 00:02:52,611 exciting things that happen after the main sequence. 39 00:02:52,611 --> 00:02:55,702 We'll mention giants, and super giants, and dwarves, and 40 00:02:55,702 --> 00:02:58,335 remnants, and all kinds of exciting explosions. 41 00:02:58,335 --> 00:03:02,914 And, in the process we will have filled out the HR Diagram, explained all of the 42 00:03:02,914 --> 00:03:07,150 things that are not main sequence stars that we have found, and piece them 43 00:03:07,150 --> 00:03:11,500 together in an interesting pattern. We will discover many new phenomena and 44 00:03:11,500 --> 00:03:15,275 some new physics that will be required to understand them. 45 00:03:15,275 --> 00:03:19,783 More this week than in any previous week, we will be addressing questions to which 46 00:03:19,783 --> 00:03:22,701 the answers is not known not just to me but to mankind, 47 00:03:22,701 --> 00:03:26,944 and so, there will be a lot of well some people think this and some people think 48 00:03:26,944 --> 00:03:28,747 that. I think that's very exciting. 49 00:03:28,747 --> 00:03:32,885 we will be acquiring more steps on our construction of the Cosmic Distance 50 00:03:32,885 --> 00:03:36,863 Ladder:, ways to measure larger and larger distances to add more and more of 51 00:03:36,863 --> 00:03:41,106 the universe to our 3D picture of things to which we can determine the distance. 52 00:03:41,106 --> 00:03:45,403 We will not be discussing this week the end to, despite the fact that clusters 53 00:03:45,403 --> 00:03:47,790 play an important role in what we talk about, 54 00:03:47,790 --> 00:03:52,240 the dynamics of the formation of clusters, the molecular clouds the come 55 00:03:52,240 --> 00:03:55,266 from and the dynamics of how clusters evolve 56 00:03:55,266 --> 00:04:00,422 are going to be relegated to our study of galaxies, since those are structures 57 00:04:00,422 --> 00:04:05,968 above stars we will relegate them to galactic studies. Although as some of the 58 00:04:05,968 --> 00:04:11,713 aspects of the physics we study will be require relativistic physics and we will 59 00:04:11,713 --> 00:04:16,756 skip that because relativity will be the topic for next week and I hope you 60 00:04:16,756 --> 00:04:17,906 enjoyed this one.