Neil deGrasse Tyson Explains “The Sunset Illusion”

chuck what's up

neil

let's get back to it ah it must be time to explain you are my you are my guinea pig explainer that's all I have to do I have 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, okay, son, s-u-n, the day after which Sunday is named. Did you know that yeah, yeah, sun, Sunday, I don't know, I mean? it just has the word Sunday it's named after the sun the seven days of the week are named after the seven classical planets just so you know and god is related to those planets so Saturday I guess is named after who uh saturn saturn and day of the moon uh the moon, I gave you a clue because you called it day of the moon so here we go and the other one is that you have to go to the equivalent god who ruled the planet and then you get the power to eliminate the seven classic planets which were mercury venus. mars jupiter saturn the sun and the moon there you have the seven objects that would wander against the background stars and the Greek word for wanderer is planitus that's great yes yes yes okay then the sun what interests me is our vocabulary to describe what is happening In Heaven is pre-Copernican, so Copernicus about 500 years ago wrote a book called Revolutionibus that was about the revolutions of the celestial bodies and realized that maybe the Earth is not at the center of all movement.

He should have called that book. it's not just 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 that the Earth is at the center of the known universe, we do not say at what time the sun reaches its position such that its upper extremity becomes visible above the rotating horizon of the Earth, no, we simply ask when the sun rises, when exactly the sun rises. sun, so there is a certain simplicity in thinking that they are at the center of all things, but do not forget that all this vocabulary predates the discovery and affirmation that the sun is at the center of that movement and not the earth, so I just want to say that now that we have the sun moving across the sky, so the sunlight was generated in the center of the sun.

We made a whole explainer video on how sunlight leaves the sun and then arrives through empty space. Well, there are gaps in that distance in eight minutes and 20 seconds and then it moves. our atmosphere and then reaches your eyeballs, then light through the vacuum of space moves at the speed of light when it passes through the Earth's atmosphere it no longer moves at the speed of light, it slows down, it slows down, it is well, every time light slows down coming at an angle towards a medium, the path of light bends the physics term for that is updated, it is reflected like a straw.

Do people still use straws? No, yes, now they are paper straws, yes, now you have a spiral, I remember them, okay. I'm old enough to remember when all straws were paper and you couldn't drink smoothies with them because the straw would collapse and then if you used it for too long, the straw would fill with water and would be completely useless. So I'm having straw problems right now, but I'll get over them just fine, so if you put a slanted straw in a half-full glass of water, you'll see that the straw bends the light as it comes out of the liquid into the air in the straw so that bending is not physically different from going from vacuum to air to a different medium of different densities.

Well, I say all this because as the sun gets closer to the horizon to set, it is actually moving faster than you see, so it refracts. It's taking the sun lower than the actual position in the sky, you think the sun is, oh, that's it, oh man, it's crazy to look, so look, so what's up? Great, so look, yeah, when the bright sun is on the horizon, right? The sun has already set, yeah. that's amazing I love it I love it so the atmosphere actually takes the light and bends it in such a way that you're watching a

sunset

that actually already happened or happened five minutes ago yeah you missed it okay Oh, that's really cool.

So what it means is that if you had a super missile and you pointed it at the setting sun and it could get there instantly, they would just miss it, it would just fly into space because that's not where the sun is, that's the image of the sun tilted in a direct line to your line of sight oh okay so now look that's cool that's really cool but wait there's more and if I act now you want two for one I'm connected fine can I pay for shipping and handling? here's two for one, so now it's

sunset

, how about sunrise?

Well, the same thing is happening on the other side of the sky when you are fine, when you see the sun rise, the sun is still below the horizon and has not risen yet. Okay, it's doing the same thing in reverse, as far as the light is concerned, it's bending it and you're seeing the light above the horizon and now you're seeing that light before the sun is there, right, so now that's great. So you'll get a few extra minutes of sunrise light and a few extra minutes of sunset light. Okay, so watch what happens if you wait until the equinox, which we say lightly: I will do it, my colleagues and everyone in the know will say globally the same day. and night equals 12 hours of day and 12 hours of night if that day you look in the tables at what time the sun rises and what time it sets it is not it does not divide the day into 12 and 12. that is why five additional minutes on each side, so actually the equinoxes give you a ten around it depends on what your latitude is but about 10 minutes more sunlight than a pure 12 and 12 would tie it in if you're one of those people who like that.

When searching for these tables, you can search for them on wiki or search for them on Google. Find the sunrise and sunset table. If you want to find the day when you really have 12 hours of sunlight and 12 hours of darkness, it won't be on the equinoxes, although I have told you that we have the same day and the same night because it's too much to explain all the rest of this which I just did, so I'll leave it at that and if you come to me later and tell me where I looked at it, Dr. Tyson. above and it's not true, come to my office now we can explain to you and now I can give you the full explanation.

Wow, that's phenomenal because I'm not going to give you that full explanation exactly if To begin with, I didn't know 12 and 12 and the origin of the word and everything else. Once you get out of the box, we'll give you the full explanation and there you have it. I'm going to need to know this as an educator at all times. My audience needs to know this at all times. So let's do that experiment. Are you ready. I will do it with you. Alright. So what is the path around the Earth's orbit? the sun, what shape does that path have? eh, so it's a round, I love that vocabulary, chuck, it's around, man, it's an envelope, it's an ellipse, if I had told you it was a circle, would you have called me?

He would have done it because he could. I would say we already had that model of the solar system, it's very good, okay, so here's the thing, if you didn't know that the Earth moves at all, then I'll probably start that explanation by saying that the Earth goes in circles around the Sun. what the sun does not revolve around the earth is okay, like that, like that, that first foray, I don't want to do it either, you don't need to get complicated yet because you want to convey the basic ideas, okay, so we. Well, we went around the circle and said wait a minute, the circle doesn't work the way we need it to, oh you know, because it's not really a circle, it's an ellipse, okay, a slightly flattened circle, which is the answer I got. you gave, so, chuck, you're happy.

With this explanation you're having with your lips, I'm fine with that, that's fine, that's because you need to know. Oh, so you're saying it's not an ellipse. The 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, now that I need to know, I can't know, so we'll have to put that in another explainer video another time. Okay, okay, let me. back to sunlight for 12 hours of the day at night, so this refraction is just a fun fact about the sun because you don't see it where it is but where the refraction of light allows you to.

I love that, that's really cool because you never look at what you're looking at and let's be done, which not only is the sun not where you think it is in the sky for all the reasons. I've given that there are other types of ghosts in the sky that I think are worthy of just being exposed when you look at the stars, yeah, okay, oh, the way they refract through these angles, and I'm just saying that that has sense. life is light light light is light in fact, when I am in a telescope observing a star, its coordinates are the pure coordinates, assuming that the Earth has no atmosphere and the telescope knows the angle at which you are viewing the star with respect to to the horizon and calculate the refractive effects of the Earth's atmosphere on that starlight and move the telescope to that position, not to the star's position in the catalog, that's great, because we have people who know how to do the same thing, yeah, yes, I'm pretty.

Sure you would need them, we have good people, but not only do those stars not only go through this refractive thing but it's light that they gave off tens of hundreds of billions and in some cases, billions of years ago, they're all just ghosts, so it may not even be there you're seeing the light of something that's not even there this is about things that may or may not exist that's really I mean, I mean, I completely get it yeah, but it's really a bit strange to think and cool because like us when you cut a flashlight there's just no way you can make out the last light that came out of the flashlight, you can't make that out because everything goes dark and you can't make that perception but what you are They say here's a super bright luminous thing in the sky, a star, it's fine and it shines for billions of years and then all of a sudden it disappears, but that whole stream of material, that light that came from it, is still there. on that path.

It's still coming at you and you're getting all that information and then in a moment it's going to disappear, but it was a long time before that guy, that's amazing, I love it, it's like the dancing fountains in the uh, I love it. those are like yeah, that's where they not only okay, it's not just there, you go to a lot of theme parks, you have this right, dancing fountains, yeah, kids play, so yeah, these are fountains that are at the right angle. and they will put a faucet with a stream of water that comes out just as the fountain turns off and you see the stream of water going, so it's like that, but with light my friend, that's fantastic, it's incredible, in fact, in fact, since you got me there, okay, if the earth were a black hole, a ray of light would do exactly what those water currents are doing around the black hole because the curvature of spacetime is that strong, you turn on a ray of light and you see the beam go up and down, right, right, yeah, oh. that's amazing, I love it, that's, oh, that's so God, the universe is so beautiful in so many ways, it's beautiful, it's beautiful, beautiful, so, that's the sun, its refraction, it's the fake sunrises and sunsets , 12 hours of day and night, and that reminds me. from that poem recited at the end of the moody blues song gentlemen in white satin did you know that no, I don't know, I know the song, oh, so you cut the song before the most beautiful part of the song came out? which is a spoken poem at the end well, I was listening to the song because you are the song the song I wanted to hear the song is fine, but at the end there is actually a recitation that begins take a deep breath the darkness that accumulates look at how the lights they fade out each room that's how it starts, but what I'm thinking about is the last line that's on the topic of this whole explainer video, but we decide which one is correct and which one is an

illusion

.

How nice, oh, I like it, what a perfect ending. what we've been talking about the sun you're a liar you're a liar son chuck that won't turn into poetry sorry okay we have to leave it there chuck it's always good to have you it's always a pleasure baby Alright, I'm Neil Degrasse Tyson, your astrophysicist staff, once again asks you to keep looking up.