00:00Many sci-fi movies can make you believe that everything happening in space is accompanied by some kind of sound effect, which is a totally false misconception.
00:11In space, no one will hear you scream. There's no air in space. It's an almost perfect vacuum.
00:17And the sound waves don't travel through a vacuum.
00:21They can't reach your eardrums and make them vibrate, sending signals to your brain.
00:25But it's a good thing, especially for astronauts on spacewalks.
00:30If not for the quietness of space, they would be constantly overwhelmed by the noise of solar storms.
00:39Huge space explosions sure look super impressive.
00:43Whether they're scientifically possible or not is another question.
00:47Blasts on our home planet look the way they do because of air and gravity.
00:52You see, the air functions as an oxidizer, and the outward pressure makes everything fly into the air and then collapse back to the ground.
01:02But this process is very different in space, and it looks even cooler.
01:07If a blast occurred in space, there would still be some fire despite the lack of air because some kinds of fuels can act as oxidizers.
01:14But it wouldn't be the fire you're imagining now.
01:18This cosmic fire would look like an expanding ball of light.
01:22It would be a seemingly never-ending process due to microgravity and the lack of air resistance.
01:29Nearby spaceships would be in grave danger since the shrapnel would fly outward until something eventually stops it.
01:36All comets have beautiful long tails.
01:42Huh?
01:43It's nothing but a popular misconception.
01:45In reality, comets are very difficult space bodies to spot.
01:50They usually spend large amounts of time far away from stars.
01:54There, in the darkness of space, they remain rather inactive and completely frozen.
02:00Comets only get tails once they come close to a star.
02:03That's when they start warming up.
02:06This process makes them form some kind of a cloudy atmosphere, which is called a coma, and a distinctive tail.
02:14The tail always points away from the star that influences the comet.
02:19It happens because the tail gets blown in the opposite direction by solar radiation and solar winds.
02:25That's why the tail can often be in front of the comet, not trailing after it.
02:30The inner and outer planets of the solar system are separated by the asteroid belt, a ring of asteroids and other debris and space objects orbiting around the sun.
02:41While creating movies about space, filmmakers make sure to somehow use this region.
02:46Usually, they show the asteroid belt as an extremely crowded place with dense clouds of huge rocks you have to skillfully maneuver to get through to the other side.
02:56In reality, if you looked outside your spaceship while flying through this region of space, it would feel as if you were looking at the sky from Earth.
03:04All because of the ginormous distances in space.
03:09If you decided to cross the asteroid belt, there would be very little chance of a collision with a space object.
03:15Asteroids there are really spaced out and very far from one another.
03:19Black holes are giant, scary, cosmic vacuum cleaners, they say.
03:27But in reality, black holes are more like fly traps.
03:30They don't look for things to munch on.
03:32Instead, they sit out there quite passively.
03:35Only when a star or any other object comes too close does a black hole spring into action.
03:41Even so, only those space bodies that cross a certain border get ripped apart.
03:45In fact, black holes aren't any different from any other celestial body since their pull is directly proportional to their mass.
03:53They can't swallow anything bigger than what their size allows.
03:58Even if our sun was somehow replaced with a black hole as massive as itself,
04:03nothing would change for Earth or any other planet in the solar system.
04:07Gravitationally speaking, of course.
04:09Space battles in movies often involve using lasers.
04:17But if you were to see such a fight from up close, you would probably be disappointed.
04:22The thing is, it would be like nothing in movies.
04:25A laser beam is a concentrated burst of energy, and it could indeed be used for many purposes during a fight.
04:31But a real-life laser beam would be totally invisible in space since there wouldn't be any particles around to scatter the light
04:39and make the beam bright red or green or any other color.
04:46A human would be torn into pieces if they got into open space without a spacesuit.
04:51Well, contrary to popular belief, taking off a spacesuit during a spacewalk wouldn't be as dramatic as it's often pictured in movies.
04:59A person would just lose consciousness due to a lack of oxygen after 15 seconds of being in outer space without protection.
05:08But that's if this person breathed out as much air as possible.
05:11Otherwise, this oxygen would damage their lungs from the inside, making them rupture.
05:17After that, without the protection of the spacesuit, the pressure inside their body would drop.
05:23This would cause even more serious trouble.
05:25And even though this person definitely wouldn't burst, they wouldn't want to stay outside for too long.
05:34People often believe that in space, you experience zero gravity.
05:39Hence, the weightlessness astronauts feel on the International Space Station.
05:43But that's not exactly true.
05:45Gravity is one of the most important forces that exist in the universe.
05:49Thanks to it, the moon orbits Earth and the sun doesn't float away, out of our home Milky Way galaxy.
05:57Astronauts on the ISS do experience the effects of gravity.
06:01But that's not full-fledged.
06:02It's microgravity.
06:04The gravity on the space station is only 10% weaker than the gravity on Earth's surface.
06:10But astronauts are constantly in freefall.
06:12The spacecraft, people inside, and all the objects aboard keep falling forward, not down, but around our planet, following a specific orbit.
06:23And since they're all falling together, the crew and the stuff inside seem to be floating.
06:29That's why astronauts can move things as heavy as hundreds of pounds with their fingertips.
06:34And even though microgravity is often called zero gravity, they are very different things.
06:40A light year must mean time, right?
06:46Not really.
06:47Light years actually measure distance.
06:50NASA's definition of a light year goes like this.
06:53The total distance that a beam of light moving in a straight line travels in a year.
06:58And since light moves at a speed of 186,000 miles per second, a light year equals almost 6 trillion miles.
07:10It may seem as if the sun is always on fire.
07:14At least that's what it looks like in pictures and in movies.
07:17But in reality, our star is a giant ball of gas.
07:21Nuclear reactions happening in its core at all times make the sun burn.
07:26Every second, hundreds of millions of tons of hydrogen are converted into almost as much helium.
07:32During this process, huge amounts of energy are released as gamma rays.
07:38Then these rays turn into light.
07:40In other words, the sun does emit blinding light and incredible heat, but it's not actually on fire because no oxygen is involved in the process.
07:49The speed of light is believed to be the ultimate barrier for people when it comes to space travel.
07:57And it's often thought to be impassable.
08:00There are many theories about what it might be like to reach that speed, but none of the equations account for going above it.
08:07And still, we know that at least one thing in the universe is faster than the speed of light.
08:12The rate of its expansion.
08:13Yep, the universe is expanding faster than the speed of light, baffling astronomers and casual sky watchers alike.
08:22Or at least we can say so in terms of the speed of different objects, like faraway galaxies relative to each other.
08:30At the moment, it's not something scientists understand well.
08:33The rate of the expansion of the universe is proportional to how far something is, too.
08:39The farther it is from us, the faster it's moving away.
08:42But even though we don't get the mechanics of it yet, we've got our proof, even though it's theoretical so far,
08:49that some particles might be able to travel faster than the speed of light.
08:54Some scientists think there could be more things out there in space that could challenge this speed barrier.
09:00All we need to do is find them.
09:02That's it for today.
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