Full transcript
0:00what does this mean if the Sun is
0:02actually rotating or seeming to rotate
0:05around us or at least is moving relative
0:07to the Stars
0:09well how we see the Sun where it's lined
0:12up relative to the Stars behind it
0:16changes throughout the year and I mean
0:19this would be very difficult to see
0:21during the day because the stars are not
0:23visible because the Sun is so bright but
0:25if you extrapolate it out knowing where
0:27it was the Sun would seem to line up in
0:29front of a different set of stars
0:32throughout the year and this might be
0:34familiar to many of you it's the so
0:36called zodiac the zodiac where the Sun
0:39seems to appear relative to us when we
0:42look at the Sun where it would be lined
0:44up with the Stars does change out
0:46through the year as it does a full as we
0:48sorry do a full 360 around the Sun so it
0:53seems to line up and that's where the
0:54zodiac comes from where the Sun would be
0:57in front of what stars and this is
0:59something we're going to talk about more
1:01in a later chapter when we talk about
1:03astrology and in essence why it actually
1:05makes no sense but we'll get there a
1:08little bit later now another thing
1:10that's important to note is that all the
1:13planets and even the moon all seem to
1:15orbit very close to this ecliptic as
1:18well so if we look at this image right
1:21here you can see the ecliptic visit has
1:23been superimposed on top of it this line
1:25right here and you can see all of the
1:27planets and the moon morrow Saturn all
1:29of these ones are very close to the
1:31ecliptic and this is not a coincidence
1:33what we find is when we look at our
1:35solar system is in essence that is very
1:38flat all of the planets orbiting the Sun
1:41all orbit on a very similar plane but we
1:46also have to talk about constellations
1:47in general because they're actually kind
1:50of important for astronomy we actually
1:52divide the sky that celestial sphere
1:55into 88 different constellations and now
1:58they're not all the same size but this
2:01is a very rough way of organizing the
2:05sky and actually being able to give
2:07directions now what do I mean by that
2:09well if the sky is divided into 88
2:12constellations
2:13and I say well this is in the Orion
2:16constellation I know the rough part of
2:19the sky that that relates to I don't
2:21know exactly where in the sky that is
2:23but it tells me a rough direction your
2:26book talks about the idea of comparing
2:28this to the States I like how it divides
2:30it into States well sure if I say it's
2:34in California I don't know exactly where
2:36that is
2:37but it gives me a pretty good idea it's
2:39a very similar thing here by referring
2:42to what constellation something's in I
2:45get a rough idea of what portion of the
2:47sky it is in and in the next video we're
2:50gonna see a more specific way of
2:52dividing it in and actually giving
2:53coordinate system but this gives you a
2:55rough idea of where in the sky something
2:57is so these constellations are still
2:59useful even if they often look nothing
3:01like what they're supposed to in fact
3:03that's not an accident either if you
3:06look at your book it describes the idea
3:08that some of these were just named after
3:10famous things so they didn't necessarily
3:12look like the objects they were named
3:15after but one last point worth noting is
3:20that these constellations aren't
3:23groupings of stars like most people seem
3:25to think many of these constellations
3:27have stars that are nowhere near each
3:29other if you look at the Big Dipper this
3:32is an actual image of how far the stars
3:34would be they are nowhere near each
3:36other it just so happens the stars
3:38appear in the same direction when we
3:40look into night sky from our perspective
3:42on earth if someone was looking from a
3:44different planet a different solar
3:45system they would see very very
3:47different constellations and so these
3:50constellations are not actual groupings
3:52of stars they are just in the same
3:54general direction what is this whole
3:57idea of angular size let's take a look
4:01at some demonstrations of this actually
4:03because angular size is an important
4:05concept it is the angle and objects
4:08takes up when you're looking from one
4:10side to the other let's jump to some
4:15examples so angular size it says this
4:20angular size of an object depends on how
4:22big the object is and how far away it is
4:24from us well let's think for a second if
4:26that makes it
4:27here's my pan my nice chewed-up and I
4:31don't know why I always chew on it well
4:34my pen is a fixed size it's not gonna
4:36change I'm not magic this pen is a pen
4:39what happens as I move it towards the
4:41camera seems to be getting bigger it's
4:45not but all that's happening is this
4:48angular size is changing as its distance
4:52from us the viewer changes so angular
4:56size and let's use my cell phone we're
5:02going to use this as a demonstration of
5:03angular size right here again angular
5:05size is if I was looking at the angle
5:09would actually take something here let's
5:10demonstrate let's say I am someone
5:12standing right here so this is me the
5:15angular size of my phone from this
5:17perspective would literally just be the
5:20angle it takes up when looking from one
5:22side to the other so this we could
5:27define as the angular size I can even
5:29give it a fancy simulator and that's
5:31just the size this object takes up from
5:33this perspective what happens if I move
5:36my phone relative so I'm still standing
5:38here
5:38go paper two-dimensional me now my phone
5:42has moved closer
5:52okay now the angular size has changed
5:56the angular size would be this distance
5:58Peter - I could even call it if I wanted
6:01to nothing changed I'm still at the same
6:03spot this phone is still the same size
6:06phone it's just because of its relative
6:09position it now seems larger to me which
6:12again is the very long way of doing this
6:14demonstration I did right here but
6:18hopefully that actually demonstrates the
6:22idea and please ask questions if not
6:25this is a concept were going to come
6:27back to especially when we started
6:29looking at our Sun and Moon combination
6:32angular size becomes very important and
6:34a whole explanation of why you get into
6:36Clips actually