# if the earth moves at over 60k MPH, why does it appear slow to astronauts? Is everything relative to the universe moving? And if so, how fast are you really going when floating in space at a standstill?

346 views

if the earth moves at over 60k MPH, why does it appear slow to astronauts? Is everything relative to the universe moving? And if so, how fast are you really going when floating in space at a standstill?

In: Physics

Because the astronauts are also moving at roughly the same speed in the same direction, they only notice the speed difference.

There is no telling how fast you are absolutely moving in space, as we can only measure it relative to something else. The only truly set speed is the speed of light. But due to special relativity even that can’t be used to measure absolute speed.

It appears slow because the astronauts have similar momentum. They are flying through space right alongside the planet at nearly the same speed; its actually very difficult to slow down to a point where you would remain in the same position relative to the sun… At which point, the sun’s gravity would pull you in, as you lower your angular velocity.

Nothing in space is generally “not moving” because micro forces of gravity still exist to accelerate objects in a particular direction, and very little exists to slow things down. These things either get caught in an orbit, slingshot off of other celestial bodies because they have too much energy… or collide with them because they are not moving in any other direction fast enough to avoid it.

The movement that you’re speaking of is the earth orbiting the sun. Everything in our solar system is orbiting the sun, including the moon, the iss, and the astronauts, so relatively speaking the earth appears to be moving slowly. You can think of it like when you’re in a car – no one in the car looks like they’re moving at 60mph, because you are too.

The entire solar system is also moving as the galaxy rotates, but we don’t perceive that either because everything around us is moving together.

If you are talking about the rotation of the earth, it is indeed rather fast – but the Earth is also really big. From orbit, you don’t really see anything smaller than a country-sized region with the naked eye, and those don’t seem to go by that fast because they’re big and “zoomed out”. If an astronaut used some sort of telescope to zoom in on everyday objects on the surface of Earth, they would look like they were going by rather quickly.

If you are talking about the Earth moving around the sun, the astronauts are moving around the sun at about the same speed (as others have mentioned).

As for how fast you are going when ‘floating in space at a standstill’ it depends what you are comparing to. Movement is relative – meaning that you cannot discuss movement without saying what it is relative to (something that isn’t really obvious down here on Earth where all movement can be assumet to be relative to the Earth). Usually someone floating at “standstill” in space is actually in orbit around something (if you were actually at standstill relative to the closest planet, you’d start falling!), so how fast they are going would depend on their distance to and the mass of whatever they are orbiting.

All astronauts are currently orbiting the earth so they are very much moving with the earth around the Sun at roughly the same speed. But, the astronauts ARE moving around the earth in an orbit at about 7 km/s. And yet the Earth has a circumference of 40,000 km. so it takes about 90 minutes to go round it once. That’s why it looks slow, because you’re using 40,000 km as a reference.

There is no “relative to the universe” speed. No absolute reference frame.

We measure speed relative to something else. Astronauts measure their speed relative to the Earth.

We measure the speed of the Earth relative to the Sun.

We measure the speed of the Sun around the Milky Way relative to the centre of the galaxy.

There is always something else to compare it to.

EVERYTHING in the Universe that we can observe is moving extraordinarily fast. Tens of thousands of miles per second, fast. Our measurements of speed are based on how fast we are traveling relevant to other things moving fast close to us.