Full transcript
0:00welcome back this week we're gonna be
0:01starting off with chapter 2 but remember
0:03we already covered 2.1 in the first week
0:06we'll reference some of those ideas I
0:08mean many of the concepts in the course
0:10will build off of previous chapters and
0:12previous ideas but in this case we're
0:15gonna be starting off with 2.2 and let's
0:17get right to it
0:19so astronomies been around for a long
0:23time in some shape or form in fact the
0:25idea of cosmology us trying to study the
0:28universe trying to understand its
0:30structure and its origin it is something
0:32people have been doing since ancient
0:34times
0:34obviously the complexity with which we
0:37do it has changed drastically the
0:38techniques the tools we have to use has
0:41changed drastically
0:42but many early societies did study the
0:46sky for a variety of reasons in some
0:49cases it was simply a religious thing
0:51they thought the events occurring in the
0:54sky above them related to their gods and
0:57might indicate displeasure or at least
0:58tell them to avoid doing certain things
1:00so but many also use it for much more
1:04practical purposes such as calendars
1:06that's what we're actually able to see
1:08in these a lot of these rock formations
1:10were actually calendars meant to line up
1:13with specific things whether it might be
1:16lining up say with the moon's phases to
1:18tell us what time month it is and in
1:20some cases it's to line up with certain
1:23times of year
1:23in fact we'll talk about stonehedge
1:25later on and see that it's an example of
1:27that but often society is needed to know
1:30when say to plant their crops for them
1:33these interests were a matter of
1:34survival knowing when to plant your
1:36crops could mean the difference between
1:38your civilization surviving or not if
1:41you weren't able to make enough food to
1:42feed everyone people are gonna die
1:45so you need to actually be able to
1:46predict what time of year it is and I
1:49mean that sounds maybe like a silly idea
1:50to us now but they didn't have a phone
1:52to look and go oh that's the day I mean
1:55they had to find a some way to predict
1:58growing seasons also a lot of people are
2:02using it for like seafaring if your
2:03culture was trying to travel well if
2:06they didn't have compass they had to use
2:08things like the Stars to try and
2:10navigate so there was a lot of very
2:12practical
2:13reasons they study this guy and started
2:15trying to actually make very simple
2:18instruments to tell them things now
2:23we're going to keep going and look at
2:25some of these early things and early
2:27models or the ideas one thing I want to
2:29mention though right off the bat you're
2:30gonna notice I'm putting a lot of dates
2:32like the birth dates and death dates of
2:34these people like Aristotle here I'm not
2:36gonna expect you to know that I would
2:38not expect you to know that Aristotle
2:40was born in 384 BCE
2:42because well I don't think that's
2:45necessarily an important detail for you
2:47to learn but I wanted to put the dates
2:49in here so you know roughly when this
2:51was occurring again like what kind of
2:53time frame we're looking at so just to
2:56give you an idea of how spaced out event
2:58some of these events are and again how
3:00early on they were like someone like
3:01Aristotle again 384 BCE before Common
3:05Era that's a long long time ago and
3:08thing is Aristotle was nice
3:12representative of his time in terms of
3:15what he believed a lot of the people had
3:18the similar beliefs to him well one
3:21thing Aristotle knew was that the Sun
3:23must be further from us than the moon
3:26they had noticed eclipses remember we
3:29talked about eclipses last week where
3:31the Sun Act he gets blocked by the moon
3:34they had noticed these events in history
3:35so they knew obviously if the moon was
3:38passing in from the Sun it must be
3:40closer to us they also understood the
3:43reason why the moon went through its
3:45phases again something we studied last
3:46week it goes through those phases
3:48because of it going around us and the
3:52sun's light hitting it so they were
3:54aware that it was a sunlight hitting and
3:57lighting the face of the Moon and that
3:58was what was causing it to go through
4:00the various phases but Aristotle also
4:04was able to argue that the earth was
4:06round something that we should all know
4:08for fact as of now and there was a
4:12couple different arguments he used for
4:13that for one thing the Eclipse Eclipse
4:19lunar eclipse in this case before we're
4:22looking at solar was why we knew that
4:24the moon
4:25could become between us and the Sun but
4:27the lunar eclipse remember that is the
4:30shadow of the earth passing across the
4:33moon and since that shadow always has a
4:37circular shape they knew earth was
4:40around because if I mean if you noticed
4:43that one's great you could argue that
4:44the world was flat and just in round
4:47shape and that we were lining it up but
4:49every eclipse every time there was a
4:52lunar eclipse it was circular no matter
4:55what angle was going on no matter what
4:57part of the earth was looking at it so
5:00he was able to from that justify that
5:02Hey look it must be a sphere because
5:05every part of it when it lines and goes
5:08across the moon is actually round so he
5:14was able to argue from that perspective
5:15that it was round but he also actually
5:17looked at the people traveling remember
5:22we talked about the celestial sphere and
5:23the Stars and then above us well what he
5:27said what Aristotle was arguing was that
5:29look if you travel far north the stars
5:33you see can actually change the Stars
5:37you see will change because eyes are
5:40getting higher up on earth you're seeing
5:42further up the celestial sphere you can
5:44actually see different stars remember
5:47you have that Zenith right above you you
5:50can see her to the horizon at 90 degrees
5:53from you that means you're not seeing
5:55the entire sky so as you get farther
5:57north what you would see the stars you
6:00see would be different and that was a
6:01very good argument to that obviously we
6:03must be moving across a curves feet
6:05surface as if it was earth was flat then
6:08we'd all be seeing the same stars so it
6:11was very convincing arguments hopefully
6:14these days well I mean there is still
6:16people who argue this in present day
6:18which is kind of silly
6:21I don't know what the conspiracy would
6:22be that would make us want the world to
6:25be round but there is quite a few
6:27compelling arguments your book lists a
6:30few others as well even I mean one being
6:33hey look we take satellite images in
6:35space and we clearly see it's a global
6:38as the satellites travel around it so