[fitswcs] Question about sign convention for VELOSYS

[patrick.wallace at stfc.ac.uk]

William,


> A question has arisen about the use of the WCS keywords SPECSYS
> and VELOSYS for solar observations.  The plan is to set
> SPECSYS='HELIOCEN', and to set VELOSYS to the radial velocity of
> the observatory relative to the physical center of the Sun, with a
> positive value if the movement is toward the Sun.  Is this the 
> correct sign convention?

I have always interpreted "radial velocity" (misnamed as it is a
scalar, not a vector) as synonymous with "recession speed", i.e. the
opposite to what you are proposing.


Patrick Wallace
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RAL Space                                            +44-1235-531198
STFC Rutherford Appleton Laboratory
Harwell Oxford
Didcot, Oxfordshire, OX11 0QX, UK         Patrick.Wallace at stfc.ac.uk
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