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Honolulu Community College |
Music You're traveling through another dimension.A dimension not only of sight and sound, but of mind.A journey over a wondrous land responding to that imagination.The next stop, the twilight zone. (Echo.)Music"We're baaaaak.It's Science 122, the telecourse that encourages you to get physical.This is Program 4, 'Earth and Space,' which correspondswith Lesson 4 in Section 1 or the Study Guide."Hey, that was really good, but, you know, it wasa little weird on the part where you said, "Baaaaak."I didn't like that.Nah, it was OK.
You know, you know, maybe there's a future for yoursilicon brain in the broadcasting industry.Not me.I could never be happy with a desk job.Before we're done with this program we will have learnedabout the celestial sphere and its geocentric motion.And we will have described the kinds of objectswe see in the sky and their motions.We will refresh our knowledge of the modern heliocentricparadigm as we prepare to place ourselves in the prespectiveof our ancient ancestors in the future programs.We will see computer animations of movements in the sky as welearn about the stars, the moon, the sun, the planets,and finally, about meteors, comets and novae.In this program we will be switching back and forthbetween the geocentric and heliocentric paradigms,much like we did when viewing the vases and faces in Program 3.We don't do this to confuse anyone.We do it, in fact, to make things simple.
So, today astronomers use a geocentric reference frameto keep track of the positions and movements of heavenly objects.But we understand the movements in heliocentric terms.So, our modern paradigm does not abandon the geocentric ideas entirely.We use it as a model when it's useful and when it's parsimonious.But we remain aware that it is only a model and we understandunder which circumstances and for what purposes we can use it.We still believe that the heliocentric model representsthe true motion, but by using both models, we can providea clearer picture than either model alone provides.
In the case of the vases and faces, when we became aware thatboth paradigms were there, we gained knowledgeabout the true nature of the figures.Similarly, by using both heliocentric and geocentricmodels, we gain knowledge about the universe.Now, compared to our distant ancestors,we're not very good observers of the heavens.Most of us, in fact, are indoors most of the time, especially at night.Besides, the light and chemical pollution from ourcities obscures all but the very brightest stars, so we couldn't see them anyway.So, in our continuing quest here to understand the scientificrevolution and to understand why it was such a big deal for peopleto understand that the earth is a planet and goes around the sunlike everybody else, I want to take us now to the beginningsof science; and that is to try to put us in the perspectiveof someone who has no knowledge already of how the planets move.This is hard for us, because we know.We've been told.We've seen pictures.We have solar system demos.We have models of the earth and the moon.We have sent spacecraft to other planets, but try to put yourselfin the perspective of someone who's never been told and has noknowledge of any kind about how the planets move,what the planets are made out of, in fact, how far away they are or anything.In other words, all you have is your knowledge of what you see up in the sky.This is hard for us.
Close your eyes, if it helps, and picture yourself sitting around a fire.It's cold outside.Your only protection from the elements is maybe a woodenhut, maybe a stone cave, maybe some animal fur wrappedaround you, and you're sitting there and the fire's cracklingand you hear wolves off in the distance howling.You get the feeling?You don't understand any of this stuff.You know what the wolves are, but you don't really know anythingabout the world except what your senses have told you.And you begin to notice up in the sky that certain things are happening.So what I want to do today is to look at what kinds of things youwould see, and I'm going to keep switching back and forthbetween our modern perspective and ancient perspectiveto try help us get into the mood to do this.OK?
I know it's hard.I know it's hard.But, let's see what we can understand about this.The first thing to look at is what's actually in the sky.Now, a hundred years ago, if I was teaching a course like this,we probably wouldn't have to spend time describing whatgoes on in the sky, because more people would havespent time looking at the sky.How many of you spend any time at all looking up at the sky?For the most part, we don't, right?For various reasons.First of all, we're too busy.Secondly, we spend most of our time indoors, and if we're notin the house indoors, we're in a car indoors, or in a bus indoors,and most of the time when we are out at night, we're in the cityand the city lights are so bright that it obscuresall but the very brightest of things in the sky.Plus, here in Hawaii, of course, with the mountains over hereand the tradewinds blowing the clouds we only have a good viewof the southern part of the sky most of the time, anyway.So, we want to take a look at this and try to get a sense of whatkinds of objects there are in the sky, and see how theclassification of these things comes about, simply basedupon the different types of motion that things undergo.Be sure to read these objectivesin the Study Guide and refer to them as you study the lesson.
Focussing on the Learning Objectives will help youto study and understand the important concepts.Compare the objectives with the study questions for this lessonto be sure that you have the concepts under control.From our perspective here on earth, it looks as if we'rein the center of a giant bubble looking out.It appears as if the stars are attached to this bubble,like the ones painted on this model.You can see from the model, it doesn't really make anydifference whether the earth is spinning inside the stars,or whether the stars are spinning around the earth.The effect is the same either way.We can't really tell.
In ancient times, some people thought that the stars werelike little holes in the black fabric of the celestial spherewhich let the light of heaven shine through.Picture yourself as being inside this giant bubble.And the bubble completely surrounds us and when we lookup into the sky we see the stars as if they're on this giant bubble.This, even today, we call the celestial sphere.The celestial sphere basically is the sphere of stars.So, on this celestial sphere we find pasted the sun,the moon, the stars and the planets.The whole celestial sphere revolves around us on a daily basis from east to west.And, of course, the sun comes up in the east,stuck on the celestial sphere, and when the sun's up, of course,it obliterates the background stars, so we don't see the stars.But at night, if you watch the stars, you find a star risingin the east and moving through the skyand setting in the west just like the sun does.
The picture on the screen is a picture taken from observatory.It's a time lapse picture showing the motionsof the stars over a few minutes of time.You can see very clearly here there's a circular motion involved.See the circles?The center of the circle is what today we would call,over the North Pole, and on the celestial sphere, it's centeredvery nearly on the star we call the North Star, the star, Polaris.I need to point out to you at this point that it wasn't until thefairly late in human history, like about 500 B.C., or so,that's certainly late in human history, right?About 500 B.C. or so that it was first recordedthat the stars revolved around Polaris.In other words, that the circular motion was noted in such a waythat you could tell that Polaris was at the center.Why does it take so long to recognize this?If you think about this.Think about looking up in the sky at night and you look up and you see the stars.You see them moving?They appear to be standing still, right?Even if you watched them really, really carefully, they don't appear to move.But, if you look at the star now and then a coupleof hours later you come back and look at it.If you're aware of the patterns and you recognize that star,and notice that whereas before it was over here,now a couple of hours later, it moved up to here.So, you have to watch it really closely and watch it for a reallylong time to understand how that particular star moves acrossthe sky and to understand that all of the starsmove together in a circular path.Of course, if our ancient ancestors would have had a time lapsecamera, they could have taken a picture like this and developedit and seen instantly that the circular motion occurs.But just understanding that the motion is circular is not an easy thing to do.So, what I'm saying here is, if you were just observing the stars,it would take you a long time of observations simplyto understand that the stars undergo this circular sort of motion.
The circles are significant, because we're going to see thatthe circle, the circular motion becomes the model.In other words, by the time we get to the ancient Greeks theypostulated for reasons that we'll understand later,that the motion is actually circles.And in fact, the paradigm that existed for the next 2500 yearsafter the Greeks insisted that any model that you builtof the universe included only circular motion.The reason for that, again, we'll get into a little bitlater as we develop the ideas here.
Well, now it's finally time to look at some animations of heavenly movements.We can visit the Planetarium which the power bookcarries in its microprocessors.Since you have the Planetarium software,why don't you introduce this topic, and be nice.OK.Here it goes.Since we spend so little time looking at the skyand wondering about it in our modern, we will now studythe motions of the stars, the moon, the sun and the planets.I have been alerted that there is a messageawaiting regarding the magic, magic, magic...That's it, that's the magic word, sky.What do you mean, magic word?I said sky before and nothing happened.Well, that really didn't count, we hadn't really started yet.OK, but who are you anyway?D. P. Hubblefield, child of the universe and astronomer at large.You can call me Dip.Dip, huh?Uhum.
OK, Dip.I guess it's your game.Oh, by the way that was really cool magic.How'd you do that?Heh, heh, heh.Hey, everybody knows what the sky is, right?Well, here's your chance to tell us about the sky whileyou earn bonus points for this lesson.Just consider the following questions and send in your essays.What is the sky?What are those things we see in the sky?How far away are those things in the sky?How big are they, and how far away is the sky and what is beyond it?
OK, get ready now as we send you back to our program.(Whoosh, splat.)The stars are attached to the celestial sphere and they rotate with it.Because of this we often refer to them as the fixed star background.It's against this background that the other heavenly objects move.Although the sky seems to contain many stars, there are onlyabout 3000 visible to the naked eye under even ideal viewing conditions.About 500 are visible under typical conditions.From earliest times people worldwide recognizedthe named patterns in the stars and built myths around them.Although different cultures have seen different patterns,our modern astronomical paradigm recognizes specific regionsof the sky by the name of some ancient Middle Easternconstellation which dominates the sky in that region.Stars vary in color and brightness.There are white stars, but there are also red, yellow, green and blue stars.And not all of the pinpoints of light we see in the sky are stars.Some are planets.
The five planets, in fact, are the brightest objectsin the sky, besides the sun and the moon.The motions of the planets are a little complex.So we'll consider them later on in the program.So, the brightest stars can be seen even in the early dawn or twilight.The dimmest stars are far dimmer than we can see with the eye alone.Fortunately, telescopes and cameras allow us to seestars which we can't really see.Not counting the sun, the moon is the largestand probably the most familiar object in the sky.Awareness of its cycles and it's regularity, are legendary in every culture.The moon's motion through the sky is accompanied by phases.Even a little observation would reveal there's a relationshipbetween the phase of the moon and its position in the sky relative to the sun.Practically everyone knows the moon goes through phases, right?Well, there are some people who don't know this.Most of us do know it, but how many of us know theprogression of the phases and how many of us really know what causes them?Most of us don't keep track of the phase of the moonbecause it's not important to us.I mean we live inside, we don't care what the phaseof the moon is, for the most part it doesn't affect our lives,but anyone who spends a lot of time outdoors becomesacquainted with the phases and their timing.
Fishermen, campers, outdoors people in general.When you do pay attention to the moon and its phases you'llnotice that the moon moves against the fixed starbackground on a daily basis much faster than any other heavenly object.You'll also notice that there's a relationship between the phaseof the moon and the location of the sun.For example, the full moon rises around sunset.Everyday it gets about 50 minutes later.A week later it will rise as a quarter moon around midnight,so it's drifted 90 degrees through the sky in one week.Not surprising, 90 degrees is one quarter of a circle,and the moon goes through a complete circle in about four weeks.You'll also notice that a crescent moon hangs low in the westernsky just after sunset or hangs high in the eastern sky just before sunrise.You might also notice that a half moon is clearly visible in the daytime sky.It rises at noon and lingers overhead as the sun sets.I've known adults, people in the 30s and 40s,who suddenly discover the daytime moon.All of a sudden, it's "Hey, the moon's out in the daytime."I know this sounds strange, but ask people you know if they'veever seen the moon in the daytime.See for yourself.How many of us would have noticed this relationshipbetween the sun and the moon.Sure.It's easy to spot the phases, but to recognize the relationshipbetween the phases and the sun would require much morecareful observation and more importantly, it would requirecaring about the motions of the objects in the sky,because they were important to us.
The moon also moves through the sky east to west like the sun.In other words, the moon rises in the east travelsthrough the sky to the west.The difference is that whereas the sun rises and sets about thesame time every day, not quite, it changes throughout the year,but the moon rises at almost an hour later every day.In other words, the lunar day is up 50 minutes longer than the solar day.So, for example, if it's sunset today when the sun's justsetting, if the moon is just here on the horizon, tomorrow nightthe moon won't come over the horizon until 50 minutes after the sunset.This also is we know today is responsible for the tidesand this is why the tidal day is not the same length per dayas the solar day, and so the tides appear at different times during the day.Here's the sun.Here's the earth, and the full moon over here.
OK, so, during a full moon, for example, the sun,the moon and the earth are lined up.During the course of one day, the earth moves around the sun in its orbit.So the earth has an orbit around the sun that's something like this.In the course of one day the earth moves about one degree in its orbit.365 days in the year, 360 degrees in a circle, so in one daythe earth moves through its orbit to a new location.The moon, however, takes only one month to go in orbit.So, that means, in one day it's gone 1/30 of a revolution.One thirtieth of the way around, what's 1/30 of 360?About 12 degrees, right?So the moon in its orbit has gone, no longer lined upwith the earth and the sun, but has now moved through its orbit about 12 degrees.So the moon is now over here.No longer lined up with the earth and the sun.So why is the moon 50 minutes later?Can you see it from this picture?Here we are on earth.We're looking back at the sun like this, seeing it juston the horizon, and we see the moon just rising on the horizon over here.Our line of sight to the sun is on the horizon.
The moon is on the opposite horizon.The next day, at sunset, looking back here at the sun,and our line of sight on this horizon is this way.We can't see the moon until we've moved this much furtheraround so that we move that extra 12 degrees around on the earth'srotation until we can see the moon coming over the horizon.Would we try to see the models of the planets and their orbits.We ran into some problems involving distance and scale.Now we can draw scale models.We can make the earth a certain size.We can scale it down by a factor over 1000,or 2,000, or 10,000, or 100,000 or a million.We can do the same with the moon and the sun and all the rest of the planets.
The problem is that the distances in space arevast compared to the sizes of the objects.In our heliocentric model of the solar system, we can't evenshow the orbits in the sizes of the planets on the same map.For example, the distance to the moon is about 250,000 miles,yet its diameter is only about 3500 miles.That means it's about 70 moon diameters between the earth and the moon.The sun is almost 100 million miles away, yet its diameteris only a little less than 10 million miles.The sun is about 116 sun diameters away from the earth.If you want a little project, you can calculate howmany earth diameters away it is.If the earth is 4000 miles in radius, how many earth diameters is it to the sun.It's 93 million miles away.
We want to try to demonstrate the relative sizes of the earth,sun and the moon compared to their distances with some numbers.Then we'll look at some pictures which represent the true scaleof the earth, sun and moon, both in terms of their sizes and their distances.So, when we're doing this, try to picture the relative sizes,both when you see the pictures on the screen, when you lookat the numbers in the Study Guide, and also when you look at the textbook.So, here's some examples:If the earth is a basketball, the moon is a softball, 25 feet away.
On this same scale, the sun would be a 180 foot diameter sphere.This will be the size of a small arena and the arena would be 2 miles away.If the sun is a basketball, the earth would be a grapenut, 100 feet away.That's about the length of a basketball court.And on the same scale the moon would be a sesame seedone quarter inch away from the earth.Can't you see that it's impossible to visualizeboth the distance and size at the same time?If the scale is small enough to see the size of the orbit,it's impossible to see the tiny planet.On the other hand, if the scale is big enoughto see the planet, then its orbit is far too big to see.On the screen we see a drawing to scale which showsthe distances between the sun, earth and moon.
The earth is 116 sun diameters from the sun.This just means we're using the diameter of the sun as a unit of measure.If you can't see the earth on the screen, it's because it's too small to see.The blue dot, which is actually here, is severaltimes larger than the real earth.The moon would be too small to see on this scale,but it's about 30 earth diameters from earth,or about 2/100 of an inch on this scale.In this picture we see the relative sizes of the earth, sun, and moon.On this scale the sun would be one half mile from the earth,and the moon would be 9 feet from the earth.So here we are.We're sitting out here at the fire.
We've managed to over some period of time, whether it'syears, months, weeks, depends upon the person who's watchingit, but we've managed to figure out that there's thisrelationship between the sun and the moon, and if we're veryclever, we might figure out if there a relationshipbetween the phases of the moon and its timing in relation to the sun.So there are two things going on here.It's not only the moon's movement and phases against the fixedstars, but also the relationship of the moon to the sun.So, if we're clever, we'll have figured that out, and we mighteven have begun to develop some sort of a calendar, some sortof a sense of the time from one full moon to the nextis about the same number of days.That isn't too hard to do, but it does involve the concept of counting, doesn't it?Well, we need to know how many days there are between one full moon and the next.You have to somehow be able to keep track of the days.Of course, that's easy enough.It's like the old prisoner scratching on the wall thing.Every time there's a, every time the night falls, you do thison the rock, and you do this some number of times.And then every time the moon's full, you put a scratchon the rock, and then next time you start over again and youdo this with the sun and this with the moon, and you can actuallycompare one by one to see if it's the same number of days.It doesn't require a very sophisticated mathematicsin terms of our own math, but it still requires some sortof accounting, it requires some sort of a way to keep track of the things.And more than that, it takes the desire to keep track of things.
Some people have that desire, and some people don't.I probably wouldn't.I'm not the kind of person who would keep track of things,but fortunately, there are people who do that sortof thing so that we do have the records.Of course, the sun is very familiar to us as a ball of lightin the sky that heats the land and gives us sunburn.Of course, we set out clocks by it and it rules our livesby providing light and energy for our activities,but then it withdraws it on a daily cycle.From our perspective here on earth, the sun moves around the sky from east to west.If we were interested, and if we took the time to notice,we might see some changes in the patterns of movement of the sunthrough the fixed star background, but also against our own local horizon.
So now, you know, I'm talking about, you know, an individualhere who's sitting around the fire noticing this,and now you start to become really curious.And you wonder, you know, what else is thereabout the stars that might be interesting?So you start paying closer attention.And then you start to notice that at sunrise, for example.You know, you're up in the morning because you have to go outand you know, hunt the bear and things like that.So you look out, and just before the sun rises, you notice there'sa particular group of stars on the horizon.So, you're sitting here and you're looking out at the horizonand just for the record you might notice that there's a rockover here and over here there's a tree.And you know, you're sitting at your favorite vantage pointoutside the cave waiting for the sun to come up so youcan go out without getting eaten.And you notice that just before sunrise on this one particularmorning there's a group of stars here.And so you notice as you watch the sunrise and the sun appearsover the horizon, you notice that the sun appears here, say,and begins to obscure that background stars.So, you think this is kind of curious and don't pay much attention to it.So a few days later, a week later, a month later, some later time,you're out there again and you're watching the sunrise,and the sun's coming up, and you suddenly realize thatgroup of stars is no longer there.Instead, now when the sun comes up, that groupof stars is now up here instead.The sun's, as the horizon begins to get light,and you think to yourself, you know, I'm really sure thatbefore when that sun came up, that group of stars was here.But since you didn't have a photograph, and you didn't reallykeep records, you can't really be sure of it, right?So, then you start to notice, then the sun comes outand you notice something else very strange.I'll put this in here now, we'll come back to it later.But, you start to notice that the sun is now coming up over here instead.
Whereas before the sun was coming up right under thesestars, and now the sun's coming up over here closer to the trees.Again, you think to yourself, I'm sure the sun didn'tcome up that close to that tree before.And so then you might start to keep track of it.You might start to notice what's going on.And what you would notice is, OK, I'm going to switch back to ourmodern perspective now, is that a particular group of stars risesabout four minutes later each day.In other words, if you time the appearance of a particular staron the horizon, it changes by about four minutes a day.In our modern perspective this, of course, is becausethe earth is going around the sun.So that if today the direction's of a particular star is here,at this time of day tomorrow, when the earth has gonethrough part of its orbit, tomorrow the direction thatstar's going to be higher in the sky, a little different than it was before.OK, but four minutes a day isn't very much.Plus, we have clocks where we can, Oh, it's 11:56,we can tell the exact time that the star arises.If you don't have a clock and your only gauge is the sun, you don'treally know whether, you know, how much laterby minutes something is rising.
OK.What you would notice, if you started watching this,and started paying attention to it, that this particular groupof stars would eventually disappear altogether and wouldthen at some point start to beyond, you will startto notice it on the other horizon at sunset.So the same group of stars would disappear because now they'reonly up in the daytime and the sun obscures them, but eventuallyyou'd notice that when the sun sets over here, that groupof stars now appears in the western sky after sunset.So you begin to think, "Oh, gee."So now, the group, so you begin to try to figure this out.Right?As you keep watching you'll notice that later on,sometime later, things repeat themselves.And now you wake up one morning and you look and here'sthe group of stars, and here's the sun rising backwhere it was when you first noticed it.There's another cycle involved here.Right?
The stars progressed through sky in relation to the sun.And after a period of time, of course, now we call it a year,but that period of time, over that period of time, this groupof stars moves through the sky relative to the sun and suddenlyreappears again back in the sky in the same place.If you were really clever and you really cared about this,you might start then to say, "Wait, gee, I wonder howmany days it takes for it to do that?"If you were really clever.It might take many people, it might take ten years before youget to the point when you say, "Yeah, maybe I should keep track of this."Right?So, keep in mind when I'm talking about this and saying, you know,one person's doing this, probably no one person ever did this in a lifetime.Simply because there's too much recordkeeping.But you know, father could pass on to son the idea to keep count,and if the son was interested, he might or pass it onto the daughter, or she might, right, keep track of it.OK?
So, here we begin to get to the concept that there's not onlythe monthly cycle of the moon, but also a yearlycycle between the sun and the stars.Now let's focus on the sun, itself.Some of the stuff we know.The sun moves daily from east to west.It moves westward in relation to the celestial sphere.That's what I was saying here before, right, the sun doesn'tstay in the same place relative to the stars.It seems day to day to get further away from a particular star group.The path of the stars, of the sun, through the fixed starbackground is called the ecliptic.And every year the sun takes basically the same path.On certain day of the year the sun will bein the same place relative to the fixed stars.So, suppose now that you got to the point where you recognizethat there's this cycle between the sun and the stars.So then you start concentrating on the fact that the sun,let's forget about the stars for a minute, but the sun rises in a different place.So, you wake up one morning and you notice the sun risesabout half way between the tree and the rock that youcan see from your sunrise vantage point.By the way, everything I'm going to say hereabout sunrise also applies to sunset.Just it happens in the west instead of the east.
OK, so you watch the sun and the next morning you wake upand you look at the location of the sun and you say, "You know,I think the sun was more in the middle yesterday than it is today."So you decide to watch it and see what happens to it.Does anybody know what happens to it?It moves along the horizon.So that day after day, next day you notice the sun rises over here.Now if you were really clever, I mean if you were really clever,and you started to notice that the sun was moving, you mightfor reference points, put up a stick or something thatlines up with where the sun is.There were many early cultures that did this sort of thing.
Stonehenge in England, as an example, there's MedicineWheel in Wyoming, where the native Americans built thishuge wheel where you can stand in the center of it and markthe sunrise and sunset locations at different times of the year.So you notice that over time, the sun appears to drift along the horizon.I'll leave that stick there.Until suddenly, it appears that from day to day itmoves a little bit less each time.Now this would be hard to recognize, right, becauseif you really wanted to keep track of this, you need to put a stickevery day you'd have to have your assistant thereand say, "OK, a little bit further that way."And you line up the stick with where the sun is.But you would notice, if you did this, is that, I'm goingto exaggerate this, let's say you do it every week,you'd find that sunrise is here and next weekit rises here and next week it rises here,and next week it rises here, and here, and here,and here, and here, and that the lines where it riseseveryday and every week, in other words, it moves alittle bit less along the horizon until it hardlymoves at all and it appears almost to stand still on the horizon.
Don't get me wrong.I don't mean it stands still during the course of a day.I mean that over the course of day after day,after day, after day, it doesn't move along the horizon.You would probably notice eventually that it reaches a maximum point over here.In other words, it goes sort of, edges over here, getsto this point and appears to stay there for several days during sunrise.Again, not during the day, but each sunrise it appears to occurin the same place, but then it slowly starts day after dayand it moves back this way again as it passesthe center point here, it moves really a lot.
Each week it moves really a lot and then it does the same thing on the other side.Starts to slow down until it reaches some maximum point over here.Again, where it appears to stand still.The word for this particular location on the horizon iscalled solstice in our modern language.It comes from the word,italics sol, italics means sun.Comes from the Latin word italics stare italicswhich means to stand still.Same basis as the word for static and stasis.
OK.So, you'd find that day after day the sun appears to moveacross the horizon and it reaches some maximum locationon the horizon, appears to stay there at sunrise for severaldays and then starts to move very slowly across the horizon day after day.It speeds up again on the way back.In fact, if you could do a time lapse movie of thisof the sunrise location each morning, you'd find that it sortof resembles a pendulum, going back and forth, moving fastin the center and moving slow on the edges.So, here, for example, this is a painting,But it's a painting of the December sunrise, and you have some landmarks here.Just to keep track of things.The next picture I actually took the colors out so you can see it better.
So, here's due east.Of course, if you were living ten thousand years ago you didn'thave a compass, you didn't know this was called east.But it's called east by the way because that's theaverage position of the sun.In other words, what we would call due east on our moderndirectional system, is right here in the center,half way between the two solstices.So, here's the December sunrise.You'd find that in June what we now call the monthof June, the sun rises way over here.And there's a pretty large difference on the horizon.The difference here in Hawaii, for example, is about 45 degrees.In fact, if you haven't noticed this before,your assignment is to watch the sunset.How do you explain this?And how would you explain this?It's hard enough to explain, I mean, it's easy enoughto explain that the sun is going around you day by day,but it appears as if the sun is sort of doing this, going around youand turning like this, and turning like this, and so if you have an explanation. For example, that like the ancient Egyptians did, that there aregods who pull the sun to the sky on flaming chariots.
Every morning the sun's born and the chariots grab it and drag itthrough the sky and it dies in the evening and the next morninganother group of chariots pulls it through the sky.You'd say, "Well, I guess the sun could be born anywhere it wants to."But in terms of a scientific explanation, in termsof a logical, consistent explanation, this is a really hard thing to explain.We also find, if we paid close attention to this, thatfrom our perspective here on earth, if we watch the pathof the sun through the sky, we would find that the sun risesin the northeast in the June solstice.In other words, up here in June in the northeast, and the pathit takes through the sky is a high path.And in fact, the noonday sun, when the sun is directly overhead,it's higher in the sky in June than it is in December.You noticed that, haven't you?No, don't look at the sun.Oh, there it is, up there.It can burn your eyes out, but it's one of thosethings that we sort of take for granted.The sun comes up and it passes through the sky,but nobody pays attention to where it goes.Here we're looking down on the earth at the Equinox as if wewere looking at the earth from the sun.The sun's directly over the Equator and it illuminatesthe half of the earth which faces us.Notice as we look down directly on the Equator we see bothpoles and every point on earth has six hoursof sunlight and six hours of darkness.That is on a given longitude line.Longitude lines are like the sections of an orangerunning through both poles.All points emerge from the shadow at the same time,so all points experience sunrise at the same time.
Now, as we shift our perspective to look down on the North Poleat the Equinox, we see that each point on the same longitudecomes out of the shadow, that it experiences sunrise at the same time.Each point on the earth's surface experiences sixhours of daylight and six hours of darkness.That's what Equinox means, equal night.Now let's look at what happens at the solstices.So, here we are three months later, June 21,the summer solstice in the northern hemisphere.Because of the earth's tilt of 23 1/2 degrees, the North Poleis now pointing slightly toward the sun.So now we're looking down on the northern hemisphere.We can see the North Pole, but we can also seeover the North Pole, all the way to the Arctic Circle on the other side.This means that locations in the northern hemisphere have muchlonger days than points in the southern hemisphere.
Let's take a look from another angle.Now, if we swing around to the other side of the earth,or actually one quarter of the way around the earth where we cansee how the earth's tilt affects the lengths of the day,we can see the places in the northern hemisphereexperience more sunlight the further north they are.At a particular longitude line, a point in the northernhemisphere comes into the light before a point in the southernhemisphere indicating that the sun rises earlier in the northernhemisphere and later in the southern hemisphere.If we stop the motion here you can also see that thedirection of sunrise is high in the northeast.The lines of latitude follow an east west direction,and the direction to sunrise will always beperpendicular to the terminator or shadow line.Notice that from any point on the earth, the directionof sunrise is to the north, of east.This is also true in the southern hemisphere.In fact, it's true that from everywhere on earth, the sunrises in the northeast at the June solstice.Now let's go to six months later, to the December solstice.We notice as we watch the world turn, that from this perspectivewe see the South Pole illuminatedand the Antarctic Circle we can see on the other side of the pole.
Now the North Pole is pointed away from the sun,so the southern hemisphere has the sun shining directly on it.In fact, the sun is now shining directly over the 23 1/2 degreelatitude and the days are longer in the southernhemisphere than they are in the northern hemisphere.Now, if we go again one fourth of the way around the earth,we can see how the tilt affects the hours of daylightin both hemispheres here at the December solstice.Now we see that the northern hemisphere isin darkness longer than the southern hemisphere.And we see that all locations in the southern hemisphere emergeout of the darkness and experience sunrise earlierthan any location in the northern hemisphere.Again, notice that a point on the Equator experiences six hoursof daylight and six hours of darkness.Just like before, we can determine the general direction of sunrise.A line of latitude runs east west and a direction perpendicularto the terminator points to the sun.
At sunrise, the sun is to the south of east in both hemispheres.In the southern hemisphere that direction south of east bringsa particular location out of the shadow at an earlier time thanin the northern hemisphere, so the days are longer in the southernhemisphere and the sun rises earlier and sets later.In this picture we see how the tilt of the earth causes the circleof illumination to be tilted relative to the poles.We're looking at the South Pole at the December solstice.Note that about 66 1/2 degrees called the Antarctic Circle,the sun does not set at all, just 24 hours of daylight,the so-called midnight sun.Let's go quickly to the North Pole to see what it looks like.On the other end of the earth, at the North Pole, we see that thetilt causes the North Pole and all locations down to 66 1/2degrees, what we call the Arctic Circle to be in darkness.Here the sun doesn't rise at all.The result of this is that each pole experiences sixmonths of light and six months of dark.Imagine living in a place where each day and each night is half a year long.The heavenly objects that have attracted the mostattention over the years are the Wanderers.The Wanderers are the planets, and the five planets visibleto the naked eye are Mercury, Venus, Mars, Jupiter and Saturn.
Now the planets move against the backgroundstars, sometimes erratically from night to night.The movement is slow, but definitely noticeable.If you care to keep track.But who would?Everything else in the sky appears to be very orderly and themotion of the planets is very orderly except during this verysmall period of time when they go retrograde.It's the retrograde motion that really requires explanation.It really drove people crazy.If it wasn't for that, we might still not know that the planetsare, that earth is a planet and goes around the sun like everything else.Because the other orderly motions are easy to understand.The final category of heavenly objects is the short duration objects.Now these things show up in the sky from time to timeand it's somewhat irregularly.While the motion may be fast, like a meteor or slow like a comet,whose motion resembles that of a planet.Or they may not move at all, like a nova, which is a new starthat shines brightly for a few months and then disappears.Some comets do appear with regularity.The most famous, of course, is Halley's Comet which lastappeared in 1986, but it's not scheduled again until 2062.So by the time you finish this section, you should be ableto clearly distinguish between these threecategories of heavenly objects.
Occasionally weird things appear in the sky.Meteors, comets and occasionally a star brightens up and flaresup until it becomes the brightest thing in the sky.We call these today a nova or supernova.While watching the sky any dark night you'll see, whew, meteor tracks.These were called falling stars for many years.In fact, some people still call them fallingstars--mistakenly.The key here and the part of this that I want to point out that'simportant to us is that people assumed that theseobjects were close to the earth.The reason they assumed they were close to the earth issimply that the idea developed that the stars, themselves,were fixed in place and were inalterable and couldn't change.So, anything new which appeared in the sky had to be somethingwhich was near earth because near earth is where thingschange, and that the heavens are unchanging except in this orderly fashion.
Well, in this program we have seen how the sun, the moon,the stars, and the planets moved through the sky asseen from our perspective here on earth.We've tried to show how these apparent motions arisefrom our understanding of the heliocentric paradigm.Now be sure to study the text assignment and pay specialattention to the figures, diagrams and boxes.The better your understanding of what we see in the heavens,the better you'll relate to the upcoming programs where wetrace the development of the geocentric paradigmand its eventual overthrow and replacement by Leocentrism.
So, now we're ready to tackle the beginnings of science.But we're out of time for this program.So, we'll do that next time."That's another episode in the Nature of Science.We hope you'll join us next time."Hey, that's very good.At this rate, it won't be long before you don't need me at all."That is the plan."Well, that's it for this time.Remember, when it comes to science, get physical.Bye.Music
