content, format, ctype, or xtype ?

[Petr Skoda]

>> I don't think that this covers all the bases, as there is also the POS 
>> expressed as sexagesimal - but running with this idea, what about a set of 
>> secondary UCD words format.MJD, format. ISO8601, format.STC, format.hms, 
>> format.dms to be added to time.epoch etc.
>>


Hi,
I am hardly following the discussion (doing still some other work)
but I like most the set of this format.something . However, I am afraid 
that the most tables from stellar astronomy will have not MJD bud HJD 
(heliocentric corrected JD).

Unlike radial velocity, which is referenced to the barycenter etc (so does 
have the meaning of reference (barycentic , heliocentric etc) shift of 
coordinate system but the clearly defined units (km/s) , and MJD which is 
just time expressed in other "units" but generaly the same as dmy+hms, 
ISO8601 .... is the HJD implying both time transformation and shift of 
reference system (to the barycenter - even it called "heliocentric")

I cannot imagine how to express this using other scheme (even in STC
what would be said ?
Time TT HELIOCENTER MJD 54964.798264

or Time TT GEOCENTER HJD 54964.798264  or other permutations ...

I am afraid that still most tables in astronomy are published in 
electronic appendices of articles in journals (maintained by Vizier ...) 
and the authors will not bother with conversion of values of their long 
tables into required format. So the scheme should be flexible to be able 
to express today yet unknown time scales and positions

And many stellar people are talking about time dependence in variable 
stars but they think about phase (time folded with estimated period)
So its "time" axis without units ! Its mostly used in describing light 
curves of variable stars or pulsations .....


So the extensible ucd seems to be reasonable for these cases.

*************************************************************************
*  Petr Skoda                         Phone : +420-323-649201, ext. 361 * 
*  Stellar Department                         +420-323-620361           *
*  Astronomical Institute AS CR       Fax   : +420-323-620250           *
*  251 65 Ondrejov                    e-mail: skoda at sunstel.asu.cas.cz  *
*  Czech Republic                                                       *
*************************************************************************