keyword units
Peter Bunclark
psb at ast.cam.ac.uk
Tue Jul 15 05:37:29 EDT 1997
One of the heated internal debates we had recently at the RGO was about
whether
keyword units should be SI units; we ended up putting the telescope
focus in
metres, whereas mm is far more natural.
A general point is, I think referring to the IAU style-guide is a `cop
out',
having read the FITS Users Guide I did just that, and the style guide is
targeted
at something completely different, ie published papers. A
machine-readable
standard has to be far tighter.
In the example I just mentioned of telescope focus, SI units are pretty
silly in
fact, so I would welcome an official blessing on being able to use
`engineering units'.
William Pence wrote:
>
> 1234567890123456789012345678901234567890123456789012345678901234567890123456789
> EXPOSURE= 1800.0 / [s] elapsed exposure time
> V_HELIO = 16.23 / [km s**(-1)] heliocentric velocity
> LAMBDA = 5400. / [angstrom] central wavelength
> FLUX = 4.9033487787637465E-30 / [J/cm**2/s] average flux
>
There should be a table of combination units, eg [km s**(-1)], which
have to be strictly adhered to to make parsing easy. So if your
velocity is standard, then your FLUX would have to be in units
of [J cm**(-2) s**(-1)]
And finally, I leave you with this thought:
DATE-OBS= 1997-07-15 / [UTC] today's date.
Peter.
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