[fitswcs] Paper III and radio/optical velocities

[Arnold Rots]

... and the difference between FK5/J2000 and ICRS(no equinox!) :-)

Richard McMahon at IOA wrote:
> 
> Hi Paddy,
> 
> 	I wish I could do a smiley.
> 
> 	I'll include the terminology in my next graduate course on
> observational astronomy. In there with subject's like the differences
> between B2000 and J2000 and epoch and equinox.
> 
> best regards richard
> 
> On Mon, 30 May 2005, Patrick Leahy wrote:
> 
> > Date: Mon, 30 May 2005 17:37:49 +0100 (BST)
> > From: Patrick Leahy <jpl at jb.man.ac.uk>
> > To: Richard McMahon at IOA <rgm at ast.cam.ac.uk>
> > Cc: fitswcs at donar.cv.nrao.edu
> > Subject: Re: [fitswcs] Paper III and radio/optical velocities
> >
> >
> > 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
> >
> 
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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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