Measure of Distance to Stars

[Wizardsblade]

Main Question or Discussion Point

When a star or galaxy etc is said to be 10 light years away is that from a standard earth's velocity distance (ie with out length contraction) or do we take into account earths velocity and gravitation and have a standard length (maybe accordance with the milkyway being stationary or if we perhaps know about where the big bang was and derive a standard distance from its stationary frame.) A follow up question would be What percent distance would be changed if we did/did not use such frames for standard distances?

 

[jtbell]

For a crude estimate of these effects within the Milky Way at least, consider that the speed of the solar system with respect to the center of the galaxy is about 220 km/sec, according to http://encarta.msn.com/encyclopedia_761558916/milky_way.html. What length-contraction factor does this speed produce?

 

[Fredrik]

...if we perhaps know about where the big bang was...

The big bang didn't happen at a point in space, and isn't an event in space-time. It's just a name for the limit where the time coordinate of a certain coordinate system goes to zero. The distance between any two objects with constant spatial coordinates in that coordinate system goes to zero in that limit. That's what the "big bang theory" is about. It's not about an explosion somewhere in space.