earth’s rotation speed from perspective


One point on the earth’s surface moves 460 meters in one second from A to B which would look very fast if you would be very near to earth frozen in place looking at it. I know that’s not possible because your position is relative to earth and there is no absolute center in the galaxy and that it is always about relativity to something and stuff, which I also don’t really get.

But I am just wondering right now, how come it looks so slow from so far away?

In: 0

A car looks slow from far awar too, and your hand looks fast if you move it right before your face. It’s just perspective.

Your field of vision is more or less a cone. It’s narrow close to your face and wide far away. But your brain doesn’t recognise that perfectly.

You don’t have any way to just judge speed like a radar gun. You can only judge perceived distance (across your field of vision) over time.

Putting those two together, something up close to your face will spend little time in your field of vision. It’s “fast”. Something far away takes ages to cross your entire field of vision. It’s “slow”. Even if in reality the thing far away is traveling several times faster.

>But I am just wondering right now, how come it looks so slow from so far away?

Same reason a plane looks pretty slow from the ground even though they’re likely flying hundreds of miles per hour.

It’s parallax. You don’t notice the distance they travel, what you see is the angle they move. Close up, something only has to move slightly to have a big change in angle. Further away, a large distance only produces a small change in angle.

Put a finger up right in front of your nose. Close one eye and then the other. Even though it’s not actually moving, the change in angle means it looks like your finger is moving a lot.

Now hold your finger out in front of your nose at arms length and do the same thing. It still looks like it’s moving, but not by nearly as much, because the angle is smaller.

That’s parallax.

Same reason why when you’re moving in a car, the houses near you look like they’re moving the same speed you are, but the skyscrapers in the distance don’t look like they’re moving very fast, even though they’re moving the same distance relative to you.

It doesn’t matter if it’s you that’s moving or the thing you’re looking at, it’s the same effect.

Not sure how ELI5 this is, maybe more ELI15, but it needs to be to talk about angles:

Your ability to judge how fast something is moving is only based on how quickly it moves through your field of vision. So like other said, if you wave your hand in front of your face, it looks fast because it is crossing your entire field of vision, which is about 120 degrees in a couple tenths of a second. For reference, if you were 100 feet away from a road, a car would have to be traveling almost 400 miles per hour to cross your entire field of view in 0.2 seconds. A car traveling at 60 mph would only cover about 1/6 of your field of view in those 0.2 seconds, so it would look like it is moving at 1/6 the speed. A plane flying at 550 mph up in the sky would only cover about .2% of your field of view in those same 0.2 seconds. So it would look to you like it is moving 500 times slower than your hand. That plane would need to be flying almost 160000 miles per hour to look like it is moving as the same speed as your hand waving in front of your face. It would need to be going almost 50000 miles per hour to look like it was going as fast as the car referenced above going 60 miles per hour 100 feet away.

In short, it is all about how quickly an object moves through your field of view that you determine how “fast” it appears to be moving to you. Something much further away has to be at much much much greater speeds to appear to be moving the same speed as something much closer traveling at much slower speeds.