VOUnits RFC

[Norman Gray]

Arnold, hello.

On 2013 Jul 26, at 19:29, Arnold Rots <arots at cfa.harvard.edu> wrote:

> This reminded me that I should quote the units allowed in the draft
> of FITS WCS Paper IV:
> 
> recommended:
> 
> s: second
> d: day (= 86400 s)
> a: Julian year (= 365.25 d)
> cy: Julian century (= 100 a)
> 
> also acceptable:
> 
> min: minute (= 60 s)
> h: hour (= 3600 s)
> yr: Julian year (= a)
> ta: tropical year
> Ba: Besselian year

I take I should therefore add these to the FITS 'known units' table in the document (and library), as recommended and deprecated, respectively.

Given the language in paper IV section 4.2, I suspect that these are _all_ in fact 'recommended' units in the sense of this IVOA document (even if paper IV would encourage authors to quote times in seconds rather than minutes), but that 'a' is preferred to 'yr'.  Does that sound plausible?

The current list of FITS 'known units' was taken from tables 4.1 and 4.2 in the FITS v3.0 spec (Pence et al., 2010).  Would that plus these units in WCS IV be complete?

At present, all of 's', 'd', 'a', 'min', 'h' and 'yr' are mentioned but not deprecated, and 'cy', 'ta' and 'Ba' aren't mentioned.  What do you think of 'ha' -- hecto-year -- as a century?  The VOUnits document states that 'ha' should be interpreted as a century, because the SI document gives only rather grudging acknowledgement of the hectare; but that was a toss-up.

All the best,

Norman


-- 
Norman Gray  :  http://nxg.me.uk
SUPA School of Physics and Astronomy, University of Glasgow, UK