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Prais'd be the fathomless universe For life and joy, and for objects and knowledge curious Walt Whitman, Leaves of Grass |
Assignments:send me an email telling me something interesting about yourselfRead Chapter 1 of your Text
check out the web pages on images you saw in class today:
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In Class:chose this slide of the gax NGC2997 as the first image you see in this course, because it depicts many of the important themes we'll discuss - it's unimaginably big - constructed of 100's billions of stars - light takes 150,000 years just to get across it that means even at warp factor 7, Captain Kirk would need more than 20,000 years to get the Enterprise across this galaxy. - but that's nothing compared to how far away from us it is - light from it takes 55 million! years to travel to us - the light reaching us today was emitted by the stars in this gax when dinosaurs were still walking around on Earth - even though some of the objects in our universe are huge, they're dwarfed by the distances in between - the fact that we can see this gax at all tells us a lot about the universe -- it's really far away -- but there's nothing blocking our view -- in fact, that's true for a number of distant objects -- go outside and try to look at something a mile away -- it's hard to do -- Why? -- too much nearby stuff in the way -- our local environment is really crowded -- but you can see really distant objects in space Why? -- because there's nothing in the way -- space is really empty; it must be - So the universe is constructed of huge objects like stars and gax, separated by vast distances of empty space -- it is highly structured, NOT smooth - in fact, the universe is structured on nearly all scales -- not only are gax separated by distances huge compared to their size -- stars within galaxies are too -- distances between stars, even in crowded regions of gax are huge compared to the size of a star. - light can travel across the diameter of our Sun in about 5 seconds - nearest neighbor is 4 light-years away -- even our SS is highly structured and mostly empty -- Earth-Sun dist = 10,000 times Dearth -- even Moon is more than 30 Dearth -- even atoms are mostly empty space -- on all scales, the universe is mostly empty space with a few little widely-separated nuggets -- very contrary to our everyday, crowded experience OK, so we've got this highly structured, really big, mostly empty universe, which is going to be hard enough to study since we'll have to learn about structures on so many different scales, but to make matters worse, it keeps changing on us. It's hard to believe that something as apparently unchanging as the night sky is evolving, but it really is, and often on human timescales. one night in 1987 (when you were no doubt fast asleep), the sky changed radically with the explosion of a star. now stars don't explode every day, but when they do, they make a big mess - spilling their guts out over the mostly empty space - releasing an incredible amount of energy - manufacturing new elements - the flotsam of SN explosions is what we (and everything around us) is made of --> important for evolution of the universe even worse, while you're sitting here comfy in your seat, there's a monster at the center of our galaxy that's eating a star the size of our Sun every 30 seconds Massive black holes suck in matter never to be seen again and there's one in the center of our gax don't fret; after all, it is 30,000 light years away with all of this star destruction going on, we're going to end up with no stars at all if we don't find a way to make some new ones -- luckily Nature is already at work -- reassembling some of the material spewed out by exploding stars and others into new stars -- ultimate in recycling -- it's going on now So the universe is changing, in some cases pretty radically. It is not today the way is was yesterday and it will be different tomorrow What's more, the universe has a beginning and probably an end It is not an eternal, unchanging world, but rather a dynamic, evolving and temporal structure. |