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Oct2-11, 04:13 PM
P: 344
Quote Quote by darkhorror View Post
The way we measure speed in space is we see how fast we are going with respect to something else. If I am in space with respect to me my velocity is 0. With respect to the earth it might be .5c. With respect to something else it might be 250km/s.

Saying something is moving 250km/s is meaningless unless you say what it is with respect to.
250 km/s is the speed of the Sun's motion orbiting the MW
I don’t know how they did that measurement.
It is not with respect to “something” I believe, - but only to the center of the MW, where you have relative no motion.
If we can do such measurement, other observers in the Solar system can also. But I am not sure the result for a different space-time observer would be the same.