What is the reference frame for the radial velocity measured for a distant star?
Answer
The Sun
All measured stellar motion, including the calculated radial velocity derived from the Doppler effect, is inherently relative to a chosen reference frame. In standard astronomical measurement practice, the radial velocity calculated for a distant star represents its speed specifically relative to the Sun. If an astronomer desired the velocity relative to the galactic center, additional positional and velocity data concerning the Sun's own motion within the Milky Way galaxy would need to be incorporated into the final calculation.
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