[fitswcs] FITS WCS Time Paper

[Arnold Rots]

Thank you, Pat!

The first comments needs some thought; the second is easy:
I will just include proper references to Newcomb (1895 and 1898);
the same is true for the section on ET.

Cheers,

  - Arnold

patrick.wallace at stfc.ac.uk wrote:
[ Charset UTF-8 unsupported, converting... ]
> A couple of points to be going on with.
> 
> --------------------------------------------------------------------
> 
> A.6. GPS time
> 
>  "Note that GPS time is de?ned in terms of UTC(USNO). That is to
>   emphasize that GPS time is not de?ned in terms of TAI. GPS time
>   is only required to match UTC to within a microsecond."
> 
>   This is potentially misleading to ordinary readers.  It reads as
>   if the author is in denial that GPS time is *the* de facto
>   distribution mechanism for TAI, at least for applications that can
>   make do with 100ns accuracy.
> 
>   Anyone reading the statement "GPS time is only required to match
>   UTC to within a microsecond" is going to think that a GPS time
>   readout and a UTC readout will agree, which is clearly not true
>   (except for the fractional part).
>   
>   GPS time is really defined in terms of a specific UTC epoch, while
>   UTC is itself defined in terms of TAI.  And in practice GPS time
>   is steered to TAI.  So to say only that "GPS time is not de?ned in
>   terms of TAI" may be formally correct but it is not helpful.
> 
> --------------------------------------------------------------------
> 
> A.9. UT
> 
>  "UT was initially de?ned by Newcomb?s ?ctitious mean sun Tables of
>   the Sun, Astr. Papers Amer. Ephemeris 6, 1895 The name Universal
>   Time was established as the subdivision of the Universal Day by
>   Commission 4 of the IAU at the IIIth General Assembly in 1928 at
>   Leiden (IAU, 1928 13 )."
> 
>   This needs some brackets and other punctuation.  Perhaps
> 
>   ...by Newcomb?s "?ctitious mean Sun" (Tables of the Sun, Astr.
>   Papers Amer. Ephemeris 6, 1895). The name... 
> 
> --------------------------------------------------------------------
> 
> 
> Patrick Wallace
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> Harwell Oxford
> Didcot, Oxfordshire, OX11 0QX, UK       ??Patrick.Wallace at stfc.ac.uk
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> 
> 
> 
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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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