Patricio Ortiz says:
> a "datetime" (however it is represented) corresponds to an instant in
> time.
Well, simultaneity is not just an issue for GR. A datetime, whatever time scale is used, only makes sense with respect to the location of the observation (or a derived location such as the barycenter). Some representation with a complexity similar to STC is required to unambiguously capture that instant in full.
> Julian Date and Modified Julian Date (which do assume the usage of UTC)
> seem to be one of the most appropriate way of representing such instant
> in time. Using the ISO standard (string representation) is quite
> common,
> but any application wanting to compare instants in time needs to
> convert
> it to a floatinng number (double).
If the precision required is larger than a second (a typical case for ground based observations), an integer (long) may be preferable. A simple epsilon test may be sufficient to test for equality. A more general case may be constructing a histogram representing the passage of a wavefront (or non-EM event) - in that case we may want to consider more obscure questions like whether the histogram intervals are half-open on the top or the bottom. Deciding the simultaneity of two events that are extended in time rather than instantaneous is a more interesting question than simply whether two intervals overlap. (Even ignoring the differing physics of signal generation and propagation that may apply to two different wavelength regimes.)
Rob Seaman
NOAO
Received on 2005-04-22Z20:01:42