About the draft itself Re: WD-SIA-2.0

[Rob Seaman]

The poor defenseless metre was made of platinum-iridium and can stick up for itself:

	http://en.wikipedia.org/wiki/File:Platinum-Iridium_meter_bar.jpg

Then the standard was based on krypton and not even Superman could bash it.  Now, like most else of merit, it’s all about time.

The need to pick one unit for the entire EM spectrum is not engraved on platinum in a vault beneath the streets of Sèvres.
—

On May 6, 2014, at 3:40 PM, Douglas Tody <dtody at nrao.edu> wrote:

> Yes, wavelength is a lousy unit for high energy.  But since we have
> to pick one unit for the entire EM spectrum it is a reasonable choice.
> For discovery purposes of HE data probably the main usage is merely to
> check for a wavelength smaller than some upper limit, to find or exclude
> HE data, for which it will work ok (this is all rather pointless, I just
> don't like people bashing the poor defenseless meter and feel I need to
> stick up for it).  - Doug
> 
> 
> On Tue, 6 May 2014, François Bonnarel wrote:
> 
>> Le 06/05/2014 19:37, Douglas Tody a écrit :
>>>> PS-Yes, wavelength in meters - no one's first choice :-)
>>> Wavelength in meters is actually quite a natural unit for radio
>>> telescopes, which predominantly observe in the centimeter, millimeter,
>>> and sometimes meter wavelength ranges, although it is true that
>>> frequency is more commonly used to describe the radio bands.  O/IR and
>>> UV predominantly use angstroms, microns, and nanometers, all of which
>>> are wavelength measures.  (But I am sure this will always be a topic
>>> for heated discussion :-)
>> 
>> and Xray observers use Kev , Mev gamma ray use GeV and Tev. That's pretty small in meters.
>> I encountered the problem once in discussing with Hess/CTA group
>> 
>> Regards
>> François
>>> On Mon, 5 May 2014, Patrick Dowler wrote:
>>>> On 14/04/14 01:00 PM, Arnold Rots wrote:
>>>>> And what is "barycentric wavelength"? Conversion from frequency to
>>>>> wavelength as applied at the gravitational potential at the barycenter?
>>>>> Or does it mean to reduce the spectral coordinate to the barycenter only
>>>>> dynamically? That's pretty inconvenient for people who are doing
>>>>> Galactic work.
>>>> The intent here is that the BAND parameter only supports one unit (m) and one reference position/time/scale/hard-to-remember thing.
>>>> Since we have to pick one, can you tell me the one most suitable that would apply to BAND and TIME parameters. Note that the draft currently just refers to the same restricted time metadata as DALI uses for literal values (time scale UTC and unknown reference position). What should we use for wavelength values in the BAND parameter, knowing that implementers will actually just query the wavelength(s) they have in files, filter lookup tables, or spectral wcs already.
>>>> PS-Yes, wavelength in meters - no one's first choice :-)
>>>> -- 
>>>> Patrick Dowler
>>>> Canadian Astronomy Data Centre
>>>> National Research Council Canada
>>>> 5071 West Saanich Road
>>>> Victoria, BC V9E 2E7
>>>> 250-363-0044 (office) 250-363-0045 (fax)