content, format, ctype, or xtype ?

[Steve Allen]

On Fri 2009-05-15T21:34:54 +0200, Alberto Micol hath writ:
> If the original time was stored in UTC, but sent onto the wire
> as TT, it could be translated back to TT without any specific extra
> metadata (the leap seconds are tabulated); that is not a problem (correct?).

Not a problem so long as the table of leap seconds is readily available.

> The problem might be with the inability of translating back from TT to TDB
> --for those cases where 10^-2 seconds matter-- but in which scenario would
> that be needed? Who, in the astronomical community, is using TDB? And what
> other data/metadata would be needed to allow such TT to TDB
> conversion? (though both values could be provided if really needed).

See Lindegren and Dravins
http://adsabs.harvard.edu/abs/2003A%26A...401.1185L
all of section 4, with attention to footnote 5 where a very typical
exception is noted (in which it is often preferred to use a time scale
which ticks in step with clocks on the surface of the earth instead of
the IAU-recommended TCB and TCG).

Their discussion about the need to use a BCRS applies not only to
spectroscopy, but also to the time/phase relations for any sort of
extra-solar oscillation or pulsation.

> Are there other possibile scenarios?

Solar events such as flares, especially as observed by STEREO
http://stereo.gsfc.nasa.gov/
and their relationship to helioseismology (because the sun is 4 light
seconds across).  These desire a heliocentric (not barycentric) time
scale.

--
Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
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