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可汗向你讲述太阳系的尺度. Sal Khan美国国家航空航天局 创建




where we left off in the last video I think we were getting a reasonably good appreciation for how huge the Sun is especially relative to the earth and how far the earth is away from the Sun that most of these diagrams that we see when we in science textbooks they don't give justice in fact you know when I showed it this this Sun over here that was about five or six inches across I said you would be just this little speck about 40 feet and it wouldn't be this distance would be about 40 feet to the left or the right or would have a radius its orbit would have a radius of about 40 feet so it'd be this you know you wouldn't even notice it if you were looking at this thing over here would be this little speck orbiting at this huge huge distance if you look at this Sun over here this Sun over here if I were to draw the whole Sun it looks like would have a it looks like I would have a diameter of about 20 inches so in this situation in this situation this earth right here and this is drawn to scale this earth would not be anywhere near this close it would be it would be about about 200 feet that way or about 60 or 70 meters 60 60 meters so you could imagine if the Sun was this size sitting on something like a football field this little speck of an earth this little thing right here would be sitting on the would be sitting on the the the other 40-yard line 60 meters away so Hugh you wouldn't even notice it this is you might notice this from a distance but you wouldn't even see this thing over here and the other planets are even further well not all of the other planets obviously you have mercury you have mercury here I'll just I think where most of us are familiar with these but I'll just list them here just in case that's mercury this is Venus mercury is the smallest of the planets where it's not debated whether it's a planet Pluto is the smallest but some people debate whether it's really a planet or kind of just a large solar body or a dwarf planet or on any of those types of things but then you have Venus probably the closest in size to the earth or it is the closest in size to the earth and then you have Mars and then you have Jupiter and just to give a sense of once again how far these things are if I were to go back to the analogy of this being the size of this then Jupiter is five times further than Earth so this would be this if I were to actually do this the scale distance this would be 300 meters away 300 meters so if I had a nice big maybe medicine balled size Sun right over here maybe a basketball size a little bit bigger than a basketball this looks on my screen then I would have I would put this little this little thing that's smaller than a ping pong ball I would put this three football fields away that's how far jupiter is and then Saturn's about twice as far as that Saturn is about nine times the distance let me let me make it clear this is the earth is one astronomical unit away from the Sun roughly its distance changes it's not a perfectly circular orbit Jupiter is approximately a little bit five plus astronomical unit so a little bit more than five times the distance of the Sun to the earth and Saturn Saturn is approximately nine astronomical units or nine times the distance from the Sun to the earth so once again this would be nine football fields away or another way to think about it and be essentially a kilometer away if we had a kind of a medicine ball sized Sun this little smaller than a ping pong ball Saturn would be a kilometer away Dan I just want to really reiterate that cuz you never kind of visualize it that way because just for the sake of being able to draw it on a page you see diagrams you see diagrams that look like this and they really don't give you a sense of how small these act these planets are relative to the Sun and especially relative to their distance from the Sun and then after Saturn you have you have Uranus Uranus and then Neptune and then and then Neptune and obviously these guys are even further just to give you a sense you know it's very easy to start talking about galaxies and and and universe is and all of the or the universe but but I really just want to get you know already what we've talked about we're talking about huge distances huge scale you know we already talked about that it would take a jet plane 17 years to travel from the earth to the Sun multiply that by five about a hundred years to go from Jupiter to the Sun 200 years to go from Saturn to the Sun so you could have had you could have had a Abraham Lincoln get into a jet plane and he still wouldn't have gotten if he left from Saturn he still would not have gotten to the Sun so these are huge huge distances but we're not done with the solar system they're just to give a sense of scale so this is so this right here that's the Sun and you know each of these plants are actually narrower than these orbits so they just draw these orbits here but you would actually even see the actual planets here at this type of a scale but this is one astronomical unit right over here the distance from the Sun to the earth then you have Mars then you have the asteroid belt there you have the asteroid belt asteroid belt which also has some pretty big things in it itself and he has these things that are kind of considered almost dwarf planets things like Ceres you could look those type things up and then you have a Jupiter out here and once again we said it would take a hundred years or roughly a hundred years for a jet plane to get from Jupiter to get from Jupiter to the Sun but even if you take this whole box here which is a huge amount of distance roughly about five astronomical units it would take about 40 minutes for the four for light to get from the Sun to Jupiter so this is a huge huge distance but even this huge distance we can put it into this little box right over here this little box right over here so this whole box this whole box right over there can be fit can be fit into this box and that you need to do that in order to appreciate the orbits of the outer planets and so on this scale you would you would and and Venus and Mercury and Mars their orbits look pretty much you can't even differentiate them from the Sun there they look so close they almost look like they're part of the Sun when you look at it on this scale and then you have net you have the outer planets Saturn Uranus Neptune and then if we have a Qui per belt and this is more asteroids but these are kind of more frozen you know and when you think of ice you always think of water ice but he out here it's so cold and it's it's relatively getting dark now because we're pretty far from the Sun that things that we normally associate as gases are going to be in their solid form out here so this isn't just rocky element's this will also be things that we normally associate as gases like methane frozen methane but even here we're not done we're not even out of the solar system yet we're not even out of the solar system yet and actually just to give you a sense just to give you a sense of the scale we're operating right here I have this chart right here from the Voyager mission so the Voyager missions Voyager 1 and 2 actually Voyager 2 left a little bit earlier a month earlier the Voyager 1 is just traveling faster they left about a year after I was born a year after I was born and their current velocity just to give you a sense of how fast how fast Voyager 1 right here Voyager 1 right here is right now traveling at 60 1060 1,000 kilometers per hour that's about 17 kilometers per second the size of a city every second it's going that fast that's at least in my mind and unfathomably fast velocity this thing has been travelling roughly that fast you know it's been going around planets and getting and gaining acceleration as it went around orbits but for the most of the time it's been going in a pretty fast speed and just to translate it to people who don't relate to kilometers that's about 38,000 38,000 miles per hour so this huge huge unfathomably fast speed and it's been doing it since 1977 I was I was learning to walk and and and when I was learning to walk it was traveling at this super fast speed and then when I was learning to tie mean you know our whole lives when we're sleeping everything we're eating and yeah I'm in elementary school is still true akka ting out of the out of the solar system at roughly the speed it's velocities change but especially once it got outside of the planets it's been roughly at this at this velocity so it's just been rocketing out and I don't want to say only but it's gotten this far it's gotten this far it's gotten about if we look at on this scale it's gotten about that far right there it's about 115 116 astronomical units and to give a sense so there's two ways to think about it one syczyk wow that's really far because if we know that even on this scale you can't even see Earth's orbit so this looks like it's a pretty pretty far distance and just to give you a sense of how far 116 astronomical units are if if 2,000 years ago Jesus got on a plane I actually cut and pasted a copy of Jesus just for visualization purposes but if he got on a jetliner at a thousand km/h and went straight in that direction in the direction that Voyager Voyager would only just now be catching up to Jesus so this is a huge huge huge huge distance but at the same time even though it's a huge distance especially relative to everything else we've talked about relative to just even the the the outer reaches of the solar system we're still talking in terms of a small scale so that is that's how far voyager is and just to give a sense on this scale so this whole box over here this whole box over here can be contained in this box and when you look at this box voyagers only gotten about voyagers only gotten about that far after traveling at this unbelievable velocity for over thirty years for 3334 about 33 years and just to give you an idea of these other things Sedna right here is one of the it's it's a it's a reasonably large sized outer solar system object it's it's it's one of the farthest objects that we know of in the solar system and it has this very eccentric orbit so it gets I don't want to say relatively close but not unreasonably far away and then it gets really far away from from the app from the Sun but even Sedna's orbit so if I were to look at this so this whole box over here this whole box over here can be contained right over here so in this diagram right here you couldn't even you wouldn't even be able to see it would be like a speck how far Voyager has traveled in 33 years at 38,000 miles per hour you would not even be able to notice you wouldn't even notice that distance and even though you can't even notice that distance we still have the sun's influence the gravitational is still a the gravitational pull is still attracting things to it and this right here this right here we speculate that there's the Oort cloud and this is where the comets originate from and this is just a bunch of frozen you can almost fit you know frozen gases and ice particles and things like that but this is kind of we're starting to get to the outer reaches of the solar system in this distance right here this distance right here is about and 50,000 astronomical units 50,000 astronomical units and just to give a scale because you hear a lot about lightyears and all of that light years are about 63,000 astronomical units so if you go a Lightyear out from the cloud you will light you're out from the Sun you'll end up in in the Oort cloud the the hypothesized Oort cloud and just to give a sense another scale the Oort cloud is actually you know most of the planets orbits are roughly in the same plane but this right here is the the orbit of the planets and once again these lines are drawn too thick they're just drawn too thin as possible so that you can see them but they're still drawn too thick and this goes gets us all the way to the creeper belt but all of this over here it's all the way out to the creeper belt all the way out to all of the major planets this is pollute this is Pluto's orbit right over here this is Pluto's orbit right over here this whole diagram is only sitting in right over there you can barely see it that's this whole diagram is just that dot in this and then you can see the Oort cloud all around it it's more of a spherical cloud and we think it exists obviously you it's hard to observe things at that distance so hopefully that gives you a gaming sense of the scale of the solar system and what's really gonna blow your mind this hasn't blown your mind already is that this whole thing's gonna start looking like a speck when you even just look at the local area around in our galaxy and then much less the galaxy as a whole much less the universe as a whole anyway I don't want to get well anyway does this this is this is starting to get crazy