 Greetings, and welcome to the Introduction to Astronomy. In this week's Misconception in Astronomy, we are going to look at the idea that gravity does not exist in space. So let's find out where gravity does and doesn't exist. Well, true, and to summarize quickly, what we know is that, yes, there is gravity in space because gravity exists everywhere. What is gravity? Well, under Isaac Newton, he gave us the idea that gravity is a force between objects, so that one object would pull on the other, and another object would pull on it, and that force of gravity is equal between the two and given by this equation. Now, in order for gravity to be zero, something here has to be, either one of the masses has to be zero, which would not be possible or something has mass, and gravity would have some mass, even if a small amount, or the distance would have to be infinite, and since you can't have an infinite distance, no matter where you are, you could calculate the gravitational force between any two objects. Certainly, it would be essentially negligible if you get far enough away from any object. Now, under Einstein, we look at gravity as a bending of space and time, and again, it would never be zero. The bending would get less and less as you get farther from the object, but it would never be zero. So, gravitational force never equal to zero. So, because of that, then, why do astronauts appear weightless? And we've seen images such as this of astronauts on the space shuttle images or on the, from the International Space Station, where the astronauts are floating in space. Well, in reality, they're actually, an astronaut in orbit would be in freefall. So, actually, the force of gravity at the distance of the International Space Station is pretty close to what it is on Earth's surface. Yeah, it's a little bit less, but not that much less. It is not anywhere close to zero. So, the gravitational acceleration at the distance of the space station would still be just as much. So, why don't the astronauts feel the gravity while we do? Well, they are in a state of freefall. They are constantly falling around the planet. Why don't they crash into the planet? Well, that's because they have a high enough velocity in their orbit that as they fall down, they've moved further around in the orbit and they remain the same distance away. So, they are moving fast enough around the planet. In fact, the International Space Station orbits Earth about every 90 minutes. So, it whips around Earth very, very quickly. And at the same time, the astronauts are really in that perpetual state of freefall that allows them to simulate weightlessness. Now, if you were in a spacecraft far away from any source of gravity, then you would have essentially weightlessness, and it would act the same as it is here. Again, the gravity would never be zero. But for what we're used to looking at for astronauts in orbit, the gravitational force is still there. Now, we can actually simulate this here on Earth, and that's often done with spacecraft, sorry, with aircraft, and taking them up high in the atmosphere, and then once you reach a certain level, kind of stopping the acceleration and you just float in a freefall for a short time before picking back up again and accelerating as the plane starts to come back down to a lower altitude. So, you can actually simulate freefall for a short period of time, which allows astronauts to be able to train. It's the same kind of thing that is happening with astronauts in the International Space Station. So, let's finish up with our conclusion here. So, what we've looked at today, gravity exists everywhere in space. There is no place in space that would have zero gravity, although it will vary depending on how close you are to sources of large mass. The Earth's gravitational force near something like the International Space Station in low Earth orbit is only a little less than what we get on the surface of Earth. And we can simulate this weightlessness using aircraft and putting an aircraft into freefall for a short period of time to be able to simulate what it would feel like to be in free, in the weightless, so supposed weightless environment of space. So, that concludes this misconception on there is no gravity in space. We'll be back again next week for another misconception in astronomy. So, until then, have a great day, everyone, and I will see you in class.