I’m sitting here trying to sleep and this is keeping me awake.
In: Physics
It’s not about linear velocity. It’s about angular velocity.
You are a point on the circumference of a circle. The star is a point at the center of the circle. There is an imaginary line (the radius) connecting you and the star.
As you move around the circumference of the circle, the angle of the radius changes at a rate related to two variables: (1) your speed and (2) the length of the radius of the circle.
Think about it. If you walk 1 meter along the circumference of a circle with a circumference of 1 meter, that’s a whole lap. But if the circumference of the circle is 10 meters, a 1 meter walk is 1/10 of a lap. Your speed is the same, but the speed the angle changes at gets slower as the radius gets bigger.
It’s this angular velocity that will determine how quickly the object will move across your visual field, and thus how blurry it will look. In the case of you and the stars, the length of the radius is vast.
edit – obviously, in real life you are not orbiting the stars in the night sky. My example is about how angular velocity determines the blur, and without being able to draw a diagram, I thought the circle example was the easier to envision and communicate.
It doesn’t even have to be 50,000 years they’re just moving really slow because they’re far away I’m sure you’ve seen time lapses of the night sky the stars do move.
The stars are ridiculously far away compared to our movement.
It’s like how a mountain in the distance doesn’t change location as you walk around town.
Check back in 50,000 years from now, and the stars will be in slightly different positions. Partly due to us moving, partly due to them moving.
Because we are very slow compared how far away they are.
Imgagine you drive a whooping 150 Miles per hour with your car. Far away objects like mountains still don’t blurr because in relation to their size and distance you’re still slow.
Bushes on the roadside are a different story though.
Compare it to running 100m north. You don’t see the sun moving either. It’s just such a slight difference in position that we can’t really see it with our eyes.
Because we’re not rotating, or revolving around the sun, all that fast, really. Yes, the Equator is going more than a thousand miles an hour … but it still takes an entire day for the Earth to rotate once. And the stars are far far away. So you don’t have to turn your head very fast at all to keep your eyes fixed on one; the angular velocity has a “per day” as its frequency.
Similarly for “going around the Sun” (takes a year) or “going around Galactic center” (takes 200 million years) – big linear velocities might be involved, but the angular frequencies are pretty small.
Astronauts on the Space Station are going around the Earth about every hour and a half, but even that is just about fast enough to see the Earth move against the stellar background if you pay attention, not enough to blur or streak the stellar dots.
–Dave, turbulence in the atmosphere causes more visual difficulty than the angular motion; it’s why they ‘twinkle’
An example:
You’re in a car going very fast 100km per hour, zooming past each street light on your road: you might see a blur of those lights zipping past. But looking far into the distance you can see street lights from a different highway almost stationary moving past u much slower, they just stay in your line of sight for much longer because those lights are much further away.
This is Similar to stars.
Also the earth isn’t moving that fast relative to the size of our galaxy or even solar system and neighbouring stars.
Have you ever been on an aeroplane? They move extremely fast, then why don’t street lights from a city down there look like blurred lines?
The city and its lights are far away so it’s in our line of sight for a while and not zooming past our eyes. Stars are Extremely far away and the earth is huge.
For example you might see lights as a blurred line when the plane is taking off because the lights are zooming past very quickly as they are very close
Our actual speed through space is extremely fast, the *apparent* speed relative to objects that are trillions of miles away is very small.
It is similar to how when driving down the freeway a mountain off in the distance hardly appears to be moving relative to you, but the dashed lines on on the road are shooting by very fast.
The difference being that the stars are many trillions of times further away than that mountain top.
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