VOUnit for solar density or metallicity?

[Markus Demleitner]

Hi Marco,

On Wed, Jun 01, 2022 at 10:16:14AM +0200, Molinaro, Marco wrote:
> Example: Solar/Space Weather people use SFU
> as a really common and understood unit.
> 
> I don't expect them to be bought in to use
> 10**-22W.m**-2.Hz-1 instead of SFU.
> 
> So, if I'm to follow your reasoning, should
> SFU be in VOUnits unquoted?
> 
> Or try to force solar people to use Jansky
> (4 orders of magnitude away)?

Frankly: I think the machine-readable unit should read
10**-22W.m**-2.Hz-1 in this case.  Domain experts will translate that
to their beloved SFUs with minimal intellectual effort, non-domain
experts (and in particular machine clients) will be grateful that
they don't have to puzzle about SFU.

Writing 1e5Jy would be a distant second in my book -- you never know
when these tables leave astronomy (in particular when it's about
solar physics, which has many rather obvious non-astronomy
applications), and I doubt too many non-astronomers know about
Jansky, both the man and the unit.

> How should we cope with that?
> Let clients understand that all 10**-22W.m**-2.Hz**-1
> means SFU?
> Adding extra metadata to define when it means SFU
> and when not?

Call me a mainstream astronomy bigot, but I'd like to suggest that
the translation from 10**-22W.m**-2.Hz**-1 to SFU is mainly a
presentation problem -- I have total sympathy for people who want to
write SFU in their plots or papers rather than something that looks
as if a hungry cat was requesting your attention while you were
typing.

But it's something that I would much rather keep outside of what
machines use when the communicate among themselves.  Turned another
way: Keeping the standards so trim that dealing with machine-readable
units is fun, clients regularly producing plots of solar system data
can use SFU even if the input data happens to use 10**-27W.m**-2.Hz-1
as its flux unit.

           -- Markus