[fitswcs] Paper III and radio/optical velocities

[Patrick Leahy]

On Mon, 30 May 2005, Richard McMahon at IOA wrote:

<SNIP>

> It would seem better to me to call them 'frequency' velocity, 'wavelength'
> velocity and 'redshift' velocity if we are trying to describe data. The
> optical/radio designations are not terms that real astronomers use.
>

Nonsense, many real astronomers use these terms all the time. 
Specifically, any radio astronomer who has had any contact with spectral 
line work will know of the two definitions and the trouble they cause. 
Obviously there are some optical astronomers (e.g. you) who havn't come 
across this before. You probably never measured a redshift small enough to 
approximate by a velocity without using a cosmological model, in which 
case the terms are indeed irrelevant for you.


Paddy Leahy