hello scholars it's dr. aber again with our last video lecture of the semester I hope you're really excited about it and in this last lecture we actually kind of combined a couple of things chapters are on the Earth System solar system and the universe and so basically when you combine all of those you generate a core concept where we examine the Earth's place in our own solar system and of course our solar system and the context of its galaxy and the universe and general broader so to begin we're gonna talk a little bit about the motion of the earth as you guys learned when we talked about seasons that the Earth revolves around the Sun and it rotates on its axis and those two words are used specifically to describe those motions so the earth has three independent motions the first is its daily rotation it takes about 24 hours to spin around on its axis that's tilted at 23 and 1/2 degrees it rotates at about 1670 kilometers an hour at the equator and so it's going around pretty fast it also has a little bit of a wobble on its wrote rotation of access so if you've ever spun a top on a on a table surface and you can see that it spins pretty nicely but it it does sometimes wobble a little bit and that's evident also and the magnetic poles as well there's a wobble and then of course it takes around 365 days to go around the Sun it's actually a little less but every four years we add a day have a leap year and to make up for that the fact that it's not perfectly 365 days so and realize that the earth does not rotate excuse me does not revolve around the Sun equally the Sun is not in the direct center of the orbit it's slightly off center so we are actually closer to the Sun this is horribly uncalibrated but we are closer to the Sun during our wintertime it's just that we're tilted away of course we described that when we got the we did the seasons so you knew that already I think there is a quiz question refreshing your memory about this when you identify the the equinoxes and solstices of course the equinoxes spring and autumn kn'l we get the earth is getting equal exposure because it's neither tilted towards nor away from the Sun so it's 12 hours of daylight and 12 hours of nighttime all over the globe whether you're in the north pole or on the equator however if you're an Alaska during the summer solstice then you're gonna get 24 hours of daylight because you will well if you're high enough in latitude because you'll never rotate out of that sunlight exposure conversely if you're in this southern hemisphere during the summer solstice it would be our our summer solstice they would have 24 hours of of darkness ok so that brings us to the moon of course the moon is about 1/6 of the size of the earth and because it's only about 236,000 miles away it has a huge gravitational impact on on the earth and so we learned about this way back in the early chapters about gravitational attraction it depends on the distance and the mass well because the munis is pretty massive it and it's only two hundred thirty six thousand miles away plus some it actually has a pole on earth and the earth pulls on the moon however because the oceans are liquid and not confined to any kind of container they get pulled towards the moon and that's what's gonna create a high tide if the Earth rotates into that that bulge so the moon's responsible for our tides the moon is about the same age as the earth we know this from the basaltic rock recovered from the Moon during the Apollo missions it has no atmosphere of course we talked about the gravity is much less because it's less massive the basaltic rock that makes up the moon is about four billion years old and a lot like Earth rocks so not too far off from Earth's age a couple of ideas behind the formation of the moon you know two main prevailing theories are that it formed at the same time as the earth during the early formation of our solar system which we'll talk about at the end of the presentation or that the more accepted idea is that the earth was struck by an early young earth was struck by an asteroid spilling its lava far enough to where it would escape a little bit of the gravitational pole and form its own oblate spheroid the moon of course you guys look up at the moon and realize sometimes it looks a little different it also sometimes is up during the day as well as at night it's just we may not notice it as much because it's not as bright compared to the black sky behind it so moon phases are going to be a quiz it a quizzed item and so you should definitely take a look at those however depending on which hemisphere of the earth that you live in if you're Australian or if you're from the southern hemisphere the moon phases are exactly backwards because you're kind of looking at it well from our perspective upside down and so it's kind of hard to envision but if you're an outer space here from the moon then excuse me if you're an outer space looking at Earth and the moon as a system you can see the sunlight is lighting one half of the moon and one half of the earth so if you're sitting here and it's whether it's daytime or nighttime the earth can rotate on its axis and so when you're coming up and looking at a daytime if you're looking at the moon it's in this direction you're not going to see anything because the unlit portion is facing us so we call it that new moon if however you're looking in that direction then you can see that the moon will be full if looking at it this way then it's gonna be a half moon so that would be the first quarter and the third quarter or last sometimes it's called another way to look at this I'll show you kind of the space perspective and the earth-based perspective so in the outer circle we have the earth-based perspective and on the inner circle we have the from outer space perspective looking at the Earth and Moon so Sun lights coming in and exactly exactly as I said before if you're on earth looking up at the moon you're not gonna see it and it's going to be completely the dark side will be facing us and so if you're looking this way you're going to see a crescent moon and if you're looking straight up it this way the first quarter this way most of it will be lit up but there's gonna be a little sliver that's not we call that the waxing gibbous moon and then it's full it takes about 28 days for the moon to revolve around the earth and one interesting rotation is that the moon's rotation is equal to its revolution so what that means is we only see one side of the Moon and it wasn't until the first Apollo missions and spending sending spacecraft up to go around the backside and take pictures of the back side of the moon it was a subject of a lot of science fiction stories about alien colonies on the backside of the moon they call it the dark side of the moon but that's a misnomer because the dark side is is only which side it's not facing the Sun so sometimes the side we look at is that is dark and sometimes it's light but one thing is true is we never get to see the back of the moon from Earth's surface so you're going to want to bookmark that page and have it handy for a couple of quiz questions eclipse is a vocabulary word that you'll come across and it just means to block out and so the adjective that defines the Eclipse tells you what it's blocking out so a solar eclipse is when you're blocking out the Sun a lunar eclipse is when you're blocking out the moon and there's a couple of questions there's a question or two on the quiz about so solar eclipses what happens is the moon is going to get in the way and of course that would be a new moon would be between the Sun and a small point on Earth's surface now we had a fortune recently to be under here in East Tennessee to be under the total Umbra or total eclipse whereas any one outside that area would be experiencing a partial eclipse and so a lot of people travel great distances to experience total eclipses and just just because they're amazing a lunar eclipse is the opposite it's when the earth gets in between the Sun and the moon and so you see Earth's shadow slowly block out the moon we also need to know the names of the planets Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Uranus not Uranus or you can say Uranus it's just I've taught middle school for so long it's easier if I just say Uranus and then all the jokes can continue Pluto was downgraded in early 2000s to a dwarf planet and the International Astronomical Union decided that there are several pieces of evidence that would remove Pluto from its classification as one of our planets it does not follow the trend where you've got the for terrestrial inner rocky planets and you've got the four Jovian gas giants and this rocky planet way out in the distance it also was downgraded because it is not in the same plane of revolution as the other planets it's a little off and and revolves at an angle sometimes it comes in between Uranus and Pluto Neptune making it not as distant as Neptune if we add Pluto then there's a couple of other astronomical bodies we would have to add to our list of planets like Ceres for example is a a really large dwarf planet near Mars and so that that's our solar system there's a couple of fun facts that you can have reference for a quiz but most of this you could just get from reading a table it's not worth necessarily memorizing any of it and so we talked about planets moons and other bodies a moon is a satellite that revolves around a planet in fact some some moons are bigger than planets just by nature of definition of a moon at the for example some of the moons of Jupiter and Saturn are larger than mercury so Titan for example a moon of Saturn and so and moons might even be you know some moons might have an atmosphere things like that so a moon is a satellite that orbits around planets planets revolve around stars we'll talk a little bit about some other small solar system bodies in a second a solar system includes a star planets moons our solar system we name the star the Sun it has eight planets over more than a hundred moons in fact even Pluto has a moon Charon or Sharon CH aro and lots of asteroids comets an astronomical unit because these distances are so great it kind of you kind of get tired of just saying you know 93 million miles and so we just basically call the distance from the earth to the Sun one astronomical unit and kind of go from there that way we can and look at things in terms of astronomical units okay so the next like eight slides are on details and specifics and facts of each individual planet and they're great to read however I'm not gonna go through those I'm gonna have them in the PowerPoint on Moodle but I'm just gonna go ahead and skip those slides for the purposes of length of this video okay so that brings us to the smaller bodies of the solar system comets asteroids and meteorites a lot of these are just debris left over from the early solar system formation and planetary formations the mass of the smaller bodies might even be about two-thirds of the total mass of our solar system so when you add them all up together it becomes significant but when you break them all up into small parts that they don't seem that significant they can hit larger objects and even cause deflections and change their trajectory of course an object in space is going to continue in motion until acted on by an outside force and so that force can be gravity and its own inertia but if it comes into contact with another object then that can potentially change its vector and trajectory so comets are believed to come mostly from the Oort cloud on the Kuiper belt and that's just outside Pluto a little further and one of the origination --zz I call the place underneath our couch the Kuiper belt and that's where the origin of dust balls comes from you'll vacuum the house and get all of them up and then one will come rolling out from from the the Oort cloud underneath the couch so you know that's it's just kind of funny how you might wonder how these things pop up and they just kind of show up sometimes one of the interesting things about comets that a lot of people don't know fun fact for the bar is that the tails always point away from the Sun and so a lot of people think the tail is left and sort of the pathway in the exact opposite direction of where the comet is going and that's incorrect in fact the comet could even be traveling this way into its own tail the tail is opposed to this direction of the Sun so we know where the Sun is in relation to this comment the Sun is what's causing that tail to vaporize they're considered to be sort of dirty snowballs are made of frozen waters and dry ice rocks and a lot of the small rocks and debris that's left behind when the Earth rotates into the pathway of that tail we get some really cool meteor showers and so the tail always points away from the Sun asteroids come mainly from a region between Mars and Jupiter so the asteroid belt is between Mars and Jupiter and there's a couple of ideas behind why that's there some say that it was a planet that existed in between Mars and Jupiter but received some sort of catastrophic impact that blasted it into a bunch of pieces and creating a debris field around the Sun at that's at that at that distance sort of like what was the name of Princess Leia's home planet Alderaan so but most people don't think that this was an albarran that was you know disintegrated a lot of the prevailing idea is that during the early formation of our solar system the gravitational tug of war between Jupiter and Mars prevented this rocky material from forming a planet so the meteoroid meteor meteorite can be kind of confusing it's kind of like driving down a street and marival and you'll be going down and it changes name three times even though you never turned and that's really the same thing they're all the same object but it's kind of where they are that makes them what they are so a meteoroid is just a small rock that's traveling through space once it enters Earth's atmosphere we call it a meteor and it starts to burn up because of friction in the atmosphere and it glows as it heats up and if it was large enough to actually impact Earth's surface then it's now a rock on Earth's surface so we add the suffix 8 meteorite to make it a rock and it's on our surface so we learned a lot about you know outerspace from analyzing meteorites and but most of them burn up of course meteors aren't as menacing or threatening to us unless they hit you directly your home car yours but of course the big scare would be asteroid impacts there's evidence of asteroid impacts on the fan in the past so you know it's it's just one of those things and the origin of the solar system is shown here it's starts as sort of a nebular cloud of debris the heavier elements are gonna be sort of gravitationally pulled towards the middle which is why the four gas planets are less dense larger less dense in fact they're less dense than water as they're just mostly gas and so the heavier elements got pulled towards the center which gives us the for terrestrial rocky planets followed by the gas giants which are composed of lighter elements and so in stage a you get the formation of the heavy elements that make up the center of the star and then the remaining stuff swirling about do later stages B and C you get gravitational contraction the spin rates going to increase and most of the mass is going to concentrate into this protostar it's the early formation of the star and then you form a solar system some solar solar systems have more than one star and where they can be binary there are many solar systems out there that we've discovered and distant galaxies and some even in our own galaxy and so basically any star could potentially have a solar system it's just a matter of finding it we call planets outside our own solar system exoplanets and we're looking for that one that's in the right distance away from its star to have water in all three states of matter for obvious reasons I hope and then that brings us to stars in the universe we've been staring at the stars as long as we've been a species and of course stars create their own light whereas planets and moons are reflected light so that's that's one of the interesting differences of objects celestial objects in the sky the stars appear to twinkle because of dust in the atmosphere and so it's really not the star themselves once you get outside Earth's atmosphere the stars don't twinkle at all you know we've got satellites and the Hubble Space Telescope outside Earth's atmosphere which is one of the reasons why we launched it we don't have the interferences of atmospheric turbulence we have what's called the celestial sphere it's sort of imaginary sphere surrounding the earth anyone who has ever been to a planetarium if you you know when you're an elementary school and they've come and blow up that big inflatable and you'd crawl in and now now they sell these star projection charts and for your children's bedroom and you can kind of see how the stars would appear from Earth and of course we see different constellations at different times of the year not because the stars themselves are moving but because the earth is one way rotating so we'll see you know pretty soon Orion start to throw his leg over the fence here and the because earth is revolving it's Earth's revolution that gives us access to view constellations so the spring time we see different constellations different star patterns in the sky compared to you know the the fall and winter and of course if you go to the southern hemisphere you'll see all kinds of constellations you've never seen before like the Southern Cross pop you know popular on the Australian flag and so it's just where you are on earth gives you access to view different constellations where the earth is on its road daily rotation would reposition the stars and again the stars aren't moving well they are but that's we'll get to that in a sec but it's really Earth's rotation that makes them appear to move and then of course it's also Earth's revolution which gives us access to view these constellations at different points so I just wanted to point out you're looking in this picture down on the lower left of this time-lapse photography graph staring up this building or tower observatory and you see it appears that the Stars are revolving around a central point and that's the North Star we call that Polaris and that's really a awesome coincidence that it happens to be right over the North Pole and it can actually be used as a point of navigation if you know where that one is follow the dipper on over to the end and you can find Polaris and use it to navigate because no matter where earth is and its rotation at whatever time of the night that's not going to be moving if you're following one of these other stars you're gonna be you're gonna be curving okay so of course I mentioned the stars produce their own light their incandescent they're powered by nuclear fusion and their core elements slamming into each other and fusing nuclei forming new elements and heavier elements the Sun is just an average star it's a yellow star you know around five thousand fifty two hundred degrees Kelvin sorry not degrees 50 to 100 Kelvin it provides a reference for understanding other stars looking out into space we see different stars and their life cycles of course few mins haven't been around long enough to really see the life cycle of a single star but when you have billions of them to look at it really puts the puzzle together because you could see them each at different stages and see kind of how they form what are the interesting things about stars is they produce you know they produce a spectrum and their spectra are analyzed we can look at the if you remember the electromagnetic spectrum visible light infrared ultraviolet and we can actually analyze the the spectra coming from the stars and and learn about their luminosity their intrinsic magnitude and there and use that to estimate how far away they are so SR has a couple of layers just like the earth it has a very hot core it's the most dense region and then you get this radiation zone that's going to radiate from energy from that central core however you get this gravitational collapse back on it you get this convection zone you can get Coronas and flares and of course that wreaks havoc on your cell phone there's the surface of the Sun as 5800 Kelvin I said 50 to 100 you know there's a little fun facts it sometimes escaped your memory so the Sun is about halfway through its lifetime based on using other stars as a proxy it was there's evidence that it was about 5 billion years ago it formed it has enough hydrogen for another 5 billion years of course the ultimate lifetime is gonna pin on its stellar mass there are two kinds of brightness there's the apparent brightness or apparent magnitude or luminosity and there's the intrinsic or basically the absolute magnitude and so the intrinsic magnitude is the actual brightness but sometimes you can't tell because a star might be a much farther away and appear to be dimmer and then another star but it's only dimmer because it's so much further away so the apparent magnitude you look up at the night sky you see the apparent magnitude that only tells you a little bit it's really about the intrinsic magnitude that tells you more about the star and of course the brightest object in the sky at night is the moon Sun during the day it drowns out the light of the stars you know you get some planetary reflections those are going to be really bright like Venus and Jupiter but then this the you know stars are going to be a little more faint the temperature of a star is also related to the brightness and its mass so some stars get up to of 30,000 Kelvin 80,000 Kelvin notices you know say degrees Kelvin it's just Kelvin and our own star of course the surface is around 5800 Kelvin and it's a yellow star there are yellow stars that can be hotter if they are more massive so the hottest stars would be blue so if you've ever seen a fire in a fireplace or a campfire and that part right above the log that's gonna be the hottest is at the blue color this is an HR diagram and you're gonna want to bookmark this because there's a couple questions on a quiz about the HR diagrams and mainly it has to do with our scientific inquiry in addition to our unit on stars but it shows the relative magnitude the wall I'm sorry not the relative the absolute magnitude along with the mass and temperature and you can also see a little bit about the lifecycle of a star and how it changes over time so I have main-sequence stars white dwarfs Giants and supergiant's and that's going to become important when we start to look at the lifecycle of a star so we're gonna start as a basically a gas cloud and nebula which is a cloud that becomes eventually a star some famous one is the Horsehead Nebula you might have seen in pictures because it looks like a horse head but gravity is going to start to pull all of this material together and it's going to condense and form a protostar and then once gravity pulls that all together you're gonna have a main-sequence star and it'll be a main-sequence star for a long time and as is our Sun it can take one of three pathways depending on the mass of that main sequence star which ultimately will depend on how much matter make that made up the nebula low mass will become a red giant and then a white dwarf and then just a some dark lump of basically coal if it has middle of mass it'll form the same but in between getting the red do I excuse me the red giant the white dwarf planetary nebula my form the high mass you will get a supernova that supernova may form a black hole or a neutron star and that's gonna depend on several things as well so of course you have the inward gravitational force being pulled and of course the outward expansion from the energy so those two forces are gonna be kind of pushing on each other and to form a star you basically get that gravitational collapse not early protostar stage there's a quiz question on this picture here and basically it is a small version of the HR diagram you've got stage of a star we name them based on their temperature and brightness different stars have different light lifetimes based on their mass and so that's gonna ultimately determine the fate of the star Milky Way galaxy is the name of our galaxy it is a spiral galaxy so it's densest stars will be concentrated in the middle and right through this region here of course you have some starters outside that as well but most of the highest concentration being in there and the center is sort of the galactic nucleus we are not at the center of that galaxy were often in the distance and there's other kinds of galaxies besides spiral galaxies and there's you know millions of galaxies each having billions of stars so it's a very vast universe the Big Bang Theory and there's a couple of different pieces of evidence that would support that and I just want to let you kind of know what scientists think a little bit about it it all started with Edwin Hubble's discovery sort of a Doppler effect of he was studying spectral lines of stars and noticed that the red lines from more distant stars had shifted and you know if you're used to studying star spectra and you understand you know the Doppler effect then it's really easy to determine that if the red lines of the spectra are shifting away that that means the galaxies that they're observing in the stars are actually moving and so they've actually calculated the expansion rate and it's very well documented it agrees with Einstein's theory of relativity independently and so what this actually means is everything is moving farther away from one another so think of if you're making chocolate chip cookies or raisin raisin bread and you've got this concentrated ball of dough and all the raisins are mixed in there and then you go to bake it what happens is the it expands as you bake it and the chocolate chips or raisins are going to be moving with the dough and expanding away from a central point from the middle point and that's exactly what's been observed in the space the stars and galaxies are are measured to be expanding so that's not hypothetical that's actual data that's been collected it's the galaxies are moving away from each other and what's more they've calculated the rate of expansion and so if you know how fast things are moving away from each other and time what if you were to take that equation and run it backwards and so if you know the rate of expansion and actually the that's actually expanding faster and faster you can run that backwards and go back in time and estimate the age of the universe and so that is what ultimately you run that back words and you come to a single point of the universe we call that a singularity and one uni verse one verse a universe and so one singularity and there's so much energy that there's that you know Big Bang and causes that expansion that we're observing and measuring you know it's getting a little bit into science fiction perhaps there's an idea of not just a single a singularity but multiple singularities that might give rise to a multiverse and so there is some idea that there will be an eventual contraction and will that be expansion forever will it be the Big Crunch so lots of really cool things to think about go off and study and become an expert at and it's just fun to think about so that's all I wanted to talk about in this screencast the last screencast I know you're all excited about that good luck on the quiz um we're gonna great lab on stars and I think that you'll like that as you start to classify stars and call or text if you have any questions Thanks