[fitswcs] FITS WCS Time Paper

[Arnold Rots]

And that is precisely what is meant, although in many cases it will
also coincide with the spacetime origin (apologies for the shorthand
term).
Like when an event arrival time is converted from (TT, topo) to
(TDB,SSB). Topo will not be the spacetime origin of TT, but SSB is for
TDB; however, at the same time a pathlength correction is applied.

This also speaks to you other point (Section 4.2.2 on p6):
a clock running TT on the surface of the geoid will appear to run at a
constant rate, but a clock running on board a spacecraft, synchronized
with TT on the geoid, will not. So, yes, we mean "wrt Earth".

  - Arnold

patrick.wallace at stfc.ac.uk wrote:
[ Charset UTF-8 unsupported, converting... ]
> I said:
> 
> 
> > I suggest taking the statement "The reference position...specifies
> > the spatial location at which the time is valid" and trying to
> > decide what is actually meant.  The only two meanings I can come up
> > with are (i) the spatial origin for a system of spacetime
> > coordinates and (ii) the topocentre, and these are different
> > things.
> 
> There is of course a third interpretation, which is the position in
> space for which a light time correction has been applied.
> 
> 
> Patrick Wallace
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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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