(0:00) Hi I'm Elliott and this is Mental Floss on YouTube, today I'm going to talk about some misconceptions about space. So I hope you like NASA, 'cause we're going to be talking a lot about them today.

(0:16) Misconception number one: the Sun is on fire. When many people picture the burning Sun they imagine something much like a campfire or an object on fire. But the Sun is actually a ball of gas. It burns things to nuclear fusion, which happens in its core. What that means is every second, 700 million tons of hydrogen gets converted into 695 million tons of helium. When this happens, energy is released as gamma rays, which get converted to light. So it emits light and heat, but it's not "on fire". In order for it to be considered "on fire", there would need to be oxygen involved, and there's not.

(0:46) Misconception number two: the Sun is the only star that has planets. Experts now believe that most of the stars in our Milky Way have planets surrounding them. Any planet that's found outside of our Solar System is known as an exoplanet, and we can be pretty sure that they exist because they affect the way a star looks. One of the most common ways to check this is to look for a decrease in light from certain stars during various times, which would indicate that a planet is orbiting it, affecting how the light appears to us.

(1:10) Misconception number three: Mercury is the closest planet to the Sun, so it's the hottest. Actually, distance from the Sun has little to do with average temperature on a planet. Venus is actually the hottest planet in the Solar System, but that's because of its atmosphere. The atmosphere contains mostly carbon dioxide and a little bit of nitrogen, making it very thick. Throughout the year the surface of Venus remains at a temperature of about 462 degrees Celsius. The surface of Mercury, on the other hand, has a lot of temperature variations. It can be as cold as -173 degrees Celsius at night, and during the day it might reach 427 degrees Celsius. Mercury has a very thin atmosphere, which is why there's so much variation in temperature.

(1:44) Misconception number four: people explode in space. Space is a near vacuum, which means that people can't survive there for more than a few minutes, but exploding isn't a concern. The body exposed in space will expand and bloat, especially the air in the lungs and the water and body tissue. But human skin is actually tight enough to prevent exploding. A person exposed to space would eventually die when circulation stops, after dissolved gases in the blood form bubbles and block flow. Basically it's like an extreme version of the "bends" that divers get, but they don't actually explode, so...just...just know that.

(2:14) Misconception number five: In the Sixties, NASA spent millions of dollars developing a pen that would write in space. So this is a popular myth on the Internet and even one episode of "The West Wing". People tend to use this as a comparison between NASA and Soviet astronauts, who were smart enough to just bring pencils. But NASA used pencils as well, and they have the receipts to prove it. In 1965, NASA placed an order for 34 mechanical pencils from Houston's Tycam Engineering Manufacturing Incorporated. There was an independent company, the Fisher Pen Company, that developed a space pen for around a million dollars. And later, both NASA and the Soviets started using Fisher's anti-gravity space pen, because it was a great pen.

(2:48) Speaking of gravity, misconception at number six: in space, you experience zero gravity. Gravity is actually considered the most important force in the universe and it doesn't just go away when we leave Earth, thank goodness. Gravity is necessary for everything from the Moon's ability to orbit the Earth to the Sun staying put in the Milky Way. What astronauts actually experience in space is what NASA calls "micro-gravity". It has nothing to do with the actual strength of gravity, which is only very slightly less on the Space Station, it's because astronauts are constantly falling, so they seem weightless.

(3:16) Misconception number seven: black holes are like vacuums. As we learn more and more about black holes, experts are more likely to compare them to Venus Flytraps than vacuums. Basically they don't suck up everything nearby, instead they sit pretty dormant, then if a star approaches it and gets too close, the black hole becomes active. And still, only some of the objects nearby get ripped apart by the black hole. But you can sometimes go through them, and come out another one, to a different part of the universe. Or at least that's what I learned in "Interstellar".

(3:42) Misconception number eight: the Moon orbits the Earth once a day. It takes about 27.3 days for the Moon to orbit the Earth, this is known as a sidereal month. Though it's worth noting that the Moon's orbit isn't considered regular, it has variations and there are upwards of five different months that astronomers recognize.

(3:56) And that brings me to misconception number nine: there's a dark side of the Moon. As the Moon is orbiting the Earth, it's also rotating on its axis, so we're always seeing the same side of the Moon no matter what. But the opposite side isn't "dark", it gets the same amount of sun as the other side.

(4:08) Misconception number ten: a light-year measures time. It actually measures distance. NASA defines a light-year as, "the total distance that a beam of light, moving in a straight line, travels in one year." Light travels at around 300,000 kilometers per second, so a light-year is around ten trillion (10,000,000,000,000) kilometers.

(4:25) Thank you for watching "Misconceptions" on Mental Floss on YouTube. If you have a topic for an upcoming "Misconceptions" episode that you would like to see, please let us know what it is in the comments down below, and I'll see you next week. Bye!