Neil deGrasse Tyson Explains “The Sunset Illusion”

[Music] chuck what's up neil we're back at it ah must be time to explain you you're my you you're my explainer guinea pig that's it i get to i get to i get to get the test case for all nations for all millions who will see this on youtube that's right okay so a couple of things uh i want to talk about the sun all right okay son [Laughter] s-u-n the day after which sunday is named okay did you know that yeah yeah sun sunday i don't know i mean it only has the word in it sunday's named after the sun the seven days of the week are named after the seven classical planets just so you know and god's related to those planets so saturday guess is named after whom uh saturn saturn and moon day uh the moon i gave you a hint there because you called it moon day so here we go and the other is you have to go to the god equivalent that ruled the planet and then you get the you can flush out the seven classical planets which were mercury venus mars jupiter saturn the sun and the moon there you go the seven objects that would wander against the background stars and the greek word for wanderer is planitus that's very cool yeah yeah yeah okay so the sun what's interesting to me is our vocabulary to describe what's going on in the sky is pre-copernican so copernicus around 500 years ago uh wrote a book called the revolutionibus which was on the revolutions of the heavenly bodies and he realized that maybe earth is not in the center of all motion he should have named that book it's not all about you that's good it probably would have sold better you know the world's first psychiatrist it's not about you it's not about you and it's not your fault right it's not your fault it's not your fault okay so our vocabulary reflects earth being in the center of the known universe we don't say what time does the sun come into position such that its upper limb becomes visible over the rotating horizon of earth no we just ask when sunrise when is sunrise exactly so there's a certain simplicity to thinking that we are in the center of all things but don't forget that that entire vocabulary predates the discovery and affirmation that the sun is in the center of that motion and not earth so i just want to say that so now so we have the sun moving across the sky so sunlight was generated in the center of the sun we did a whole explainer video on how the sunlight gets out of the sun and then it comes through the empty space all right gaps that distance in eight minutes and 20 seconds then it moves through our atmosphere and then it reaches your eyeballs okay thus light through the vacuum of space moves at the speed of light when it goes through earth's atmosphere it is no longer moving at the speed of light it slows down it slows down okay okay anytime light slows down coming at an angle into a medium the path of light bends the physics term for that is refreshed it reflects much like a straw do people still use straws no no yeah they're paper straws now yeah now you have a spiral i remember those okay i'm old enough to remember when all straws were paper and you couldn't drink milkshakes out of it because the straw would collapse right and then if you use the straw too long the straw would get water logged and it would just be completely useless okay so i have straw issues at the moment but i'll get over them all right so if you put a straw in a half filled cup of water tilted you'll see that the straw bends the light bent on its way out of the liquid into the air of the straw so that bending is no different physically from going from vacuum to air to different medium of different densities okay i say all this because as the sun approaches the horizon to set it's actually moving faster than you see it to be so refraction is taking the sun lower than the actual position on the sky you think the sun is oh that's oh man it's crazy to watch so watch so what's up great so watch yeah so when the glowing sun is on the horizon right the sun has already set yes that's amazing i love it i love it so the atmosphere is actually taking the light and bending it in such a way that you are seeing a sunset that has really already happened or it happened five minutes ago yeah you missed it okay oh that's that's really cool so what it means is if you had some super missile okay and you aimed it at the setting sun and it could get there instantly they would just miss it it would just fly off into space because that's not where the sun is that's the image of the sun bent into a direct line of for your line of sight oh that's okay so all right so now watch that's great that's really great but wait there's more and if i act now you want two for one i connect right can i just pay shipping and handling here's two for one so now that's sunset okay how about sunrise well the same thing is happening is playing out on the other side of the sky when you okay when you see the sun rise the sun is still below the horizon and has not yet risen wow okay that it's doing the same thing in reverse so it's referring to the light it's bending it and you're seeing light back over the over the horizon and now you're seeing that light before the sun is actually there correct so now that's so cool so you're getting a few extra minutes of sunrise light and a few extra minutes of sunset light okay so watch what happens if you wait around for the equinox which we glibly say i will and my colleagues and everyone who knows will globally say equal day and equal night 12 hours a day and 12 hours a night if on that day you look up in the tables what time the sun rises and what time the sun sets it is not it does not split the day into 12 and 12. because of this extra five minutes on each side so in fact the equinoxes give you ten around it depends on what your latitude is but about 10 minutes more sunlight than a pure 12 and 12 would splice it to be so if you're one of these people who likes looking up these tables you can you can wiki them or google them you look up the table sunrise sunset if you want to find the day when you actually have 12 hours of sunlight and 12 hours of darkness it will not be on the equinoxes even though i have told you we have equal day and equal night because it's too much to explain all the rest of this that i just did so i'm going to leave it at that and if you come to me later and say where doctor tyson i looked it up and it's not true come into my office now we can explain the and now i can give you the full explanation wow that is phenomenal because i'm not giving i'm not coming out of the box giving you that full explanation exactly if you didn't know the 12 and 12 to begin with and the origin of the word and all the rest of that once you once you come out of the box then we'll give you the full explanation and there you go right now you're going to need to know basis [Laughter] as an educator at all times my audience is on a need to know basis at all times so let's let's do that experiment you ready i'll do it with you okay okay so chuck um what path is earth's orbit around the sun what shape is that path uh so it's a it's a round [Laughter] i love that vocabulary chuck it's around man it's a wrap it's an ellipse had i told you it was a circle would you have called me out on that i would have because i could i would say that we are we already had that model of the solar system it's very good okay so here's the thing if you didn't know earth moved at all then i'll probably start out that explanation saying earth goes in circles around the sun what the sun doesn't go around the earth all right so so so that first foray i don't want to get too it's not you don't need to get complicated yet because you want to get the basic ideas across okay so then we put we go around circle and we said wait a minute the circle is not not working as we need oh you know because it's not actually a circle it's an ellipse okay a slightly flattened circle which is the answer you gave me so chuck you're happy with this with your lips explanation you're having i'm good with that okay good that's because you're on a need to know basis oh so you're saying that it's not an ellipse earth's actual orbit around the sun is not an ellipse oh i ran out of time in this explainer video to tell you why oh so now that i need to know i can't know so we're gonna have to put that in another explainer video at another time all right that's cool now let me get back to the sunlight in the 12 hours a day at night so this refraction is just kind of a fun fact about the sun because you see it not where it is but where the refraction of light allows you right i see it that's right that's i love that though that that's really cool because you're never really looking at what you're looking at and and let's let's let's finish it which is not only is the sun not where you think it is on the sky for all the reasons i've given there's other sort of ghosts of the sky that i think are worthy of just just putting out there all right when you look up at the stars yes all right oh by the way they refract through these angles as well just saying that that makes sense life is light light light is light in fact when i'm at a telescope observing a star their coordinates are the pure coordinates assuming earth has no atmosphere and the telescope knows the angle at which you are viewing the star relative to the horizon and it calculates the refractive um effects of earth's atmosphere on that uh starlight and it moves the telescope into that position not the position of the star in the catalog that's so cool man because we got people who know how to do that same yeah well yeah i'm pretty sure you would need those we got good people but but not only that those stars not only go through this refractive thing but this is light that they emitted tens hundreds thousands millions and in some cases billions of years ago they're all just ghosts so they may not even be there you're seeing light from something that's not even there this goes from things that may or may not even exist that is really i mean that's i mean i mean i understand it completely yes but it's really kind of eerie to think about and cool because like we when you cut off a flashlight you just there's no way you can distinguish the light that last left the flashlight you can't distinguish that because everything goes dark and you can't make that perception but what you're saying is here's this super brilliant luminous thing in the sky a star okay and it's beaming for billions of years and then all of a sudden it's gone but all of that stream of material that that those that light that came from it is still on that path it's still coming at you and you're receiving all that information and then at one point it's gonna be gone but it was going a long time before that dude that is amazing i love it it's like the dancing fountains at the at the uh i love those it's like yeah it's where they it's not just well it's not just there you go to many theme parks have this right dancing fountains yeah the children playing it so yes these are fountains that are at an angle right and they'll put a spigot of a stream of water that comes up right the fountain turns off and you see you see the stream of water going so it's just like that but with light dude that's fantastic that is amazing in fact in fact since you took me there okay if earth were a black hole a beam of light would do exactly what those streams of water are doing around the black hole because the curvature of space-time is that strong you turn on a beam of light you see the beam go up and down right right right yes oh that's amazing i love it that is oh that's so god the universe is so beautiful in so many ways it's beautiful it's beautiful beautiful so so that's the sun it's refraction it's the fake sunrises and sunsets 12-hour day and night and uh kind of reminds me of that poem recited at the end of the moody blues song knights in white satin did you know that no i don't i know the i know the song oh so you cut off the song before the the most beautiful part of the song came out which is a spoken poem at the end well i was i was listening for the song because you it's the song the song i wanted to hear the song okay but at the end there's actually a recitation it begins breathe deep the gathering gloom watch lights fade from every room that's how it begins but what i'm thinking of is the last line in it which is in the theme of this whole explainer video but we decide which is right and which is an illusion nice oh i like it what a perfect ending to what we've been talking about the sun you're a liar you're a liar son chuck that will not make it into poetry i'm sorry all right we got to drop it there chuck always good to have you always a pleasure babe all right i'm neil degrasse tyson your personal astrophysicist once again bidding you keep looking up

Channel: StarTalk

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Keywords: startalk, star talk, startalk radio, neil degrasse tyson, neil tyson, science, space, astrophysics, astronomy, podcast, space podcast, science podcast, astronomy podcast, niel degrasse tyson, physics, Chuck Nice, refraction, sunrise, sunset, sun, telescopes, equinox, ghosts of the sky, copernicus, sunset illusion, neil degrasse tyson explains, sunset science, chuck nice neil degrasse tyson, chuck nice comedy, chuck nice science

Id: 9bww_ux8NCo

Length: 16min 19sec (979 seconds)

Published: Tue Jul 28 2020