[fitsbits] Celsius unit in FITS keyword comments

[Rob Seaman]

On Mar 7, 2016, at 4:14 AM, Norman Gray <norman at astro.gla.ac.uk> wrote:

> On 7 Mar 2016, at 10:40, Forveille thierry wrote:
> 
>> I am not sure that the IVOA spec should be considered directly relevant in a FITS context. It
>> does provide background on what neighbors decided on the issue, but certainly does not
>> define the rules that apply to FITS files.
> 
> Indeed not -- I didn't intend to suggest that it did.
> 
> My message was intended as encouraging remarks from the sidelines, describing what, as you put it, neighbours decided on the same issue.  I (or indeed we) would be particularly interested in any comments on those conclusions, from this community, but we claim no authority here.
> 
> That document [1, Appx C.1] does, by the way, describes some apparent ambiguities in the FITS spec's description of its units syntax, which emerged when I tried to develop a machine-readable grammar for the syntax.  I mention this here to log it with the community.

“Good fences make good neighbors” (https://www.poets.org/poetsorg/poem/mending-wall); this is what the neighbor says. 

But what the poet says is “something there is that doesn’t love a wall, that wants it down.” IVOA and FITS are indeed neighbors, both administered through working groups of IAU Commission B2. At least one member of the commission’s organizing committee thinks IVOA and FITS should work more closely together, and that only slight attention should be paid to mending the wall between the two. We have lots of other work at hand.

Astronomers have used and will use a diversity of units. By all means the various WGs of IAU Comm B2 (Data and Documentation) should encourage neighborly adherence to common standards. But this wish goes both ways. Engineers buy off-the-shelf environmental thermometers that (at least in the U.S.) have a switch that toggles between Celsius and Fahrenheit, no Kelvin in sight. Setting circles are labeled in fractional degrees or hours. Clocks are sexagesimal. 

Measurements are sometimes converted before they are recorded, but this cannot be enforced and is often undesirable. A fundamental requirement is to be able to capture measurements in whatever units they are presented. We might encourage furlongs per fortnight to be written as a comment, but we work in a field encompassing both femtometers and parsecs. And for that matter, including speakers of many languages, and who may choose to spell the same word “neighbor” and “neighbour”.

To each the boulders that have fallen to each.

Rob