VOUnits errata-ettes

[Norman Gray]

Greetings, all.

I was pointed towards an astropy units discussion <https://github.com/astropy/astropy/pull/1911> which mentioned the VOUnits work, and in passing noticed a couple of very minor problems with the document, listed below.  I plan to fix these in the repository, so that they'll appear in any future release of the document.  None such is planned, but perhaps this would be another potential outing for the new errata process.

* The list of 'deprecated by FITS' terms in Table 2 is now clarified as deriving from Table 4 in the FITS spec (which actually says they're deprecated by the IAU but doesn't take a position on the matter itself).  I've added a note in the text.

* The besselian and tropical years are _not_ mentioned in that list of FITS-deprecated units -- they appeared by acclaim in the on-list discussions, and so ended up in the VOUnits list.  I've removed them from that column in the Unity library.

* The units 'angstrom' and 'ohm' (as unit names) are correctly spelled with a lowercase initial letter, but in both cases their usual unit _symbol_ is a non-ASCII character, so that their all-ASCII version here must be a word.  Should this be an all-lowercase word (like the unit name) or an initial-capital name, as unit-symbols derived from names (Wb, Pa, Ry, ...) usually are?  I think the latter, so that the preference in VOUnits Table 4 for 'Angstrom' and 'Ohm' as symbol names is reasonable.

I cannot imagine this causing any breakage anywhere in the world; please do feel welcome to disagree.

All the best,

Norman


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