10 Things You have Heard and Re-told but are Completely False – Neil deGrasse Tyson

Here we go. Okay, here we go. Weightless stuff left the sky. North Star's the brightest. In the dark night you can make out millions of stars. Total solar eclipses are rare. Days get longer in the summer and shorter in the winter At high noon the sun's directly overhead. Sun rises in the east and sets in the west. The moon comes out at night. What all these have in common is that they're all false Every one of these is just false, but we've heard them and we re-tell them. And we re-tell them because we assume they're true, because even that you want them to be true or they feel like they should be true but they're not. They're not. The first one: what goes up must come down. That's true if you're just human, right? If you're just flesh, whatever you throw up comes back That's kind of life experience. However we've banged golf balls on the moon that are never coming back to earth. Stuff that went to the moon reach escape velocity from Earth.

There's a speed with which you can throw things so they'll never come back to earth ever, ever. The five spacecraft that have achieved that speed in the history of the space program Pioneer 10 and 11, Voyager 1 and 2 and the New Horizons mission. Wow Yeah Okay, can I have a little more volume on that, please? More, testing… That's good, okay. I said I kinda like the other one but it's all we've got right now But I was okay, I'm holding this I was ok with this, yeah? Testing… This is kind of booming like the other one was That's right. I'm sorry with trying to work this out I'm trying. Can you hear me in the back row? Okay, okay. So, good. Ah, so… at scape velocity it never comes back, ever, it will go to the edge of the universe and never look back to earth So it's just false.

The Sun is not a yellow star, the Sun is white, right? In clock daylight, in the middle of the day, you're not looking up at the Sun because you'd be blinded by that. So then you look at the Sun when is low on the horizon, try to make its way from the crap that's in the atmosphere and all the blue and the yellow then the green filters out goes into the sky and it looks like a yellow star on the horizon is not the true color of the Sun. The true color the Sun is much better represented by when it's high up in the sky. So the Sun is just simply not yellow. By the way, if the Sun were yellow the color would snow be. Yellow There's only one place you'll find yellow snow: that's your fire hydrants? Okay? So… Weightless astronauts left Earth's gravity. That's Baloney right there.

They're weightless. Wait, they haven't even left Earth's gravity No, no, they are orbiting around the earth If they left Earth's gravity what's holding the moon in orbit? alright? Just think this through It doesn't take a grant from the NSF to understand, okay? I did this test. Nine out of ten people when asked would tell you the North Star is the brightest star in the night sky That's just not so. The North Star is not even in the Top 10 It's not even in the Top 20. It's not even in the Top 30. It's not even in the Top 40. The North Star is the 49th brightest star of the night sky. Which means you've never been visually strucked by it. You never comment "Oh my gosh! Look at the North Star!" And you're not looking at the North Star You're looking at like a planet or something Venus is out there right now.

Those who don't know that Venus is a planet. Are wishing upon it, because you wish on the first star you see tonight. That's why your wishes never come true! Because you're wishing on planets! On a dark night you can make out THOUSANDS of stars, not millions. Try counting them. You won't get pass a couple of thousand – I promise you. I've done that, ok? They send a list of who's co-sponsoring this event. There's like a strong geek index there, right? The Sci-Fi club and all this. The aeronautics and astrophysics club or whatever. So they – I bet they've counted, cause like that's what they're doing you know you do that at night. You out at the ball, we're counting stars at night. Alright, total solar eclipses are rare that's just false. Every newspaper article that reports on a total solar eclipse is "rare eclipse today" Total solar eclipses happen every two and a half years or so.

They are more common than presidential elections but they never say "rare presidential election coming up" "rare Olympics coming up" Days get longer in the summer and so this is just false. who of you believed this until I put this up? Who here believed that? Raise your hand. Ok, and the rest of you are just lying, alright. Nine hands went up – you are the honest people here, ok? The rest of y'all, I didn't see any hands over on the left side there. So days get shorter in the summer and longer in the winter. Now this is not magic thinking. Consider, consider – what is the longest day of the year. Daylight of course. What was the longest day? June, June 21st. And what else is that day? The first day of summer. So if the first day of summer is the longest day of the year then every other day in summer has to be shorter doesn't it? Another fact that didn't require a grant to figure out. What's the shortest day of the year? December 21st.

What else is December 21st? First day of winter. Every day in the winter gets longer. Sun rises in the east – actually this is true on two days of the year. Every other day it rises and sets someplace else on the horizon, for the two days that happens is on the equinoxes. The Moon comes out only at night Of course, it also comes out in the daytime, you're just not paying attention. So the problem is when you hear information you need to sort of think about, carry with you some skepticism of it. So scientists, we're aware of the way things work, we're fluent in math – that's the language of the universe – and it powers ideas, just empowers. A quick example, just a quick example – I did a poll I went up to people in the car who were not wearing seat belts, because you catch them at the red light. Do this in the spring when it's not cold enough to close the window to have heat and not hot enough to close the window and have cooling. So in the spring and in the fall, people driving with the windows open, I drop in and say – most of time they just close the window real quick – but when they don't I say why aren't you wearing a seat belt I ask the driver and the driver says things like "oh it crinkles my clothes, it constrains me" and I'm thinking where you gonna do like jumping jacks on the front of – what do you mean you're constrained? You're sitting there, right.

So they say this and they're giving all these reasons and then I ask have you ever had a class in physics? The answer is no. Had they taken a class in physics they would have known Newton's laws of motion and one of them is things in motion tend to stay in motion unless acted on by an outside force. So if you are in the car and the car is going 20 miles an hour and the car hits a brick wall the car stops but you don't stop. You keep going 20 miles an hour into the windshield, when you bust your face. So now, now people say about who you are if you don't wear a seat belt. Who here, let me ask in a different way, what speed is low enough for you to think to yourself "I don't need a seatbelt at this speed". The non seatbelt wearers in this audience answer that question for me.

Give me a speed that you're pretty sure is all is fine, Give me a speed. 30 miles an hour? There you go. 30 miles an hour, ok? 30 miles an hour, ok. Because that's not that bad 30 miles an hour. Let's go back to the physics class and let's find out something. Alright, Olympic hundred-meter sprinters – the fastest people in the world – can run 23 miles an hour. Let's round it, so 25 miles an hour. So what I want you to do you're not going to run that fast otherwise you'd be in the Olympics, so what's the fastest you can run? Maybe 16 miles an hour? Ok? So here's what you do. Find a brick wall somewhere put your hands behind your back and just run face first into the brick wall. Just do that experiment. Run as fast as you can face first into the brick wall. Then report back to me on that.

You understand the meaning of seat belts. Survival..