arXiv:astro-ph/0302522astro-ph
The fundamental definition of 'radial velocity'
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Abstract
Accuracy levels of metres per second require the fundamental concept of 'radial velocity' for stars and other distant objects to be examined, both as a physical velocity, and as measured by spectroscopic and astrometric techniques. Aiming at definitions that are unambiguous at accuracy levels of 1 m/s, we analyse different concepts of radial velocity and their interrelations. We distinguish between the geometrically defined 'kinematic radial velocity' and 'astrometric radial velocity' on one hand, and the spectroscopically defined 'barycentric radial-velocity measure' on the other. The last two concepts are defined by recent resolutions adopted by the International Astronomical Union (IAU), the motives and consequences of which are explained in this paper.
> It will go upwards, yes, but only because of an upwards velocity. In this picture, what imparted the upwards velocity to it, given its starting point on the ground? >> a falling ball [...] in reverse > it will still be accelerating downward. It seems strange to ask this of…
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