eli5: I’ve heard orbit described as continuously falling past or missing the Earth, how then do objects in geosynchronous orbit above a single point not fall out of the sky?
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Earth is also rotating, if you’re at the right altitude, the speed you need to “fall past” is one lap around the earth in 24 hours. That means you’re always over the same spot on earth, because that spot also does one full lap every 24 hours.
Earth is also rotating, if you’re at the right altitude, the speed you need to “fall past” is one lap around the earth in 24 hours. That means you’re always over the same spot on earth, because that spot also does one full lap every 24 hours.
Earth is also rotating, if you’re at the right altitude, the speed you need to “fall past” is one lap around the earth in 24 hours. That means you’re always over the same spot on earth, because that spot also does one full lap every 24 hours.
The closer you are to Earth, the faster you have to orbit to stay in orbit. For example, the International Space Station is only 254 miles away, so it has to orbit really fast (about 90 orbits per day) to stay in orbit.
The further you are from Earth, the slower you have to orbit to stay in orbit. The moon is about 240,000 miles away from Earth, so it has to orbit really slow (about one orbit every 27 days) to stay in orbit.
It stands to reason that there is a distance somewhere between those to where you will have one orbit every one day. That distance turns out to be about 22,360 miles, which as you guessed is somewhere between the close-fast orbit of the ISS and the far-slow orbit of the moon.
The closer you are to Earth, the faster you have to orbit to stay in orbit. For example, the International Space Station is only 254 miles away, so it has to orbit really fast (about 90 orbits per day) to stay in orbit.
The further you are from Earth, the slower you have to orbit to stay in orbit. The moon is about 240,000 miles away from Earth, so it has to orbit really slow (about one orbit every 27 days) to stay in orbit.
It stands to reason that there is a distance somewhere between those to where you will have one orbit every one day. That distance turns out to be about 22,360 miles, which as you guessed is somewhere between the close-fast orbit of the ISS and the far-slow orbit of the moon.
The closer you are to Earth, the faster you have to orbit to stay in orbit. For example, the International Space Station is only 254 miles away, so it has to orbit really fast (about 90 orbits per day) to stay in orbit.
The further you are from Earth, the slower you have to orbit to stay in orbit. The moon is about 240,000 miles away from Earth, so it has to orbit really slow (about one orbit every 27 days) to stay in orbit.
It stands to reason that there is a distance somewhere between those to where you will have one orbit every one day. That distance turns out to be about 22,360 miles, which as you guessed is somewhere between the close-fast orbit of the ISS and the far-slow orbit of the moon.
Imagine you’re holding one end of a rope, and there’s a ball attached to the other end. If you swing that ball around on the rope, it will move in a circle around you, with a radius equal to the taut length of the rope.
The reason for this is that the tension in the rope is constantly pulling the ball towards you. But the ball is already moving sideways relative to where you’re standing, so the ball doesn’t come straight towards you. Instead, it starts moving in another direction until the tension in the rope acts on it again, to the same effect. This creates a circular motion that continues for as long as the speed of the ball and the tension of the rope remain the same.
In this analogy, you are the Earth, the ball is a satellite, and the tension in the rope is the force of gravity (equivalent to the weight of the satellite). So as long as a satellite maintains a certain speed and doesn’t lose any mass, it will maintain a circular path around the Earth. The tricky part of setting up an orbit is getting the satellite up to the necessary speed for its weight.
Hope that helps! Let me know if you’re still confused by anything.
Imagine you’re holding one end of a rope, and there’s a ball attached to the other end. If you swing that ball around on the rope, it will move in a circle around you, with a radius equal to the taut length of the rope.
The reason for this is that the tension in the rope is constantly pulling the ball towards you. But the ball is already moving sideways relative to where you’re standing, so the ball doesn’t come straight towards you. Instead, it starts moving in another direction until the tension in the rope acts on it again, to the same effect. This creates a circular motion that continues for as long as the speed of the ball and the tension of the rope remain the same.
In this analogy, you are the Earth, the ball is a satellite, and the tension in the rope is the force of gravity (equivalent to the weight of the satellite). So as long as a satellite maintains a certain speed and doesn’t lose any mass, it will maintain a circular path around the Earth. The tricky part of setting up an orbit is getting the satellite up to the necessary speed for its weight.
Hope that helps! Let me know if you’re still confused by anything.
Imagine you’re holding one end of a rope, and there’s a ball attached to the other end. If you swing that ball around on the rope, it will move in a circle around you, with a radius equal to the taut length of the rope.
The reason for this is that the tension in the rope is constantly pulling the ball towards you. But the ball is already moving sideways relative to where you’re standing, so the ball doesn’t come straight towards you. Instead, it starts moving in another direction until the tension in the rope acts on it again, to the same effect. This creates a circular motion that continues for as long as the speed of the ball and the tension of the rope remain the same.
In this analogy, you are the Earth, the ball is a satellite, and the tension in the rope is the force of gravity (equivalent to the weight of the satellite). So as long as a satellite maintains a certain speed and doesn’t lose any mass, it will maintain a circular path around the Earth. The tricky part of setting up an orbit is getting the satellite up to the necessary speed for its weight.
Hope that helps! Let me know if you’re still confused by anything.
Think of a giant frozen lake. There’s a post in the middle with a rope tied to it.
You’re on the edge of the lake, on ice skates, holding the rope.
Try to haul yourself to the post, it’s easy: just pull on the rope.
But now imagine you’re skating hell-for-leather at right-angles to the direction of the rope.
Try to haul yourself in now, and it won’t work, all you’ll do is swing around. No matter how hard you haul on the thing, you just can’t reach the post – *your turning circle is too big to let you*.
You physically cannot by any means reach the centre of the lake without slowing down. Especially as you’re not really on ice-skates, but big blocks of wet ice that give you no traction whatsoever.
That’s orbit. That’s all it is: a big turning circle, and no way to dump your speed. You can’t just suddenly pull a 90-degree turn, so you can’t ever hit the thing you’re orbiting.
Now for geostationary orbit:
Imagine that on top of the post, there’s a carousel. One of those stately fairground ones with the horsies, which takes like an hour to go round.
Is it possible to swing around the post, but stay lined up with one particular horse?
Sure it is – if you’ve got a really huge lake and a really long rope.
If you’re skating far enough out that it takes you an hour to do a full circuit – exactly the same time as it takes one of the horsies to go round – then you’ll stay lined up. From the horsie’s perspective, you’re not moving at all.
And that’s geostationary. You have a big enough orbit, it takes 24 hours to go round the earth, the same as the continents on the surface. From their perspective, you’re not moving at all, just hovering in the air (even though you’re hurtling through space at terrifying speeds).
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