Rob Seaman wrote:

We have a large number of coadded frames to archive.
Many of these are coadds of dithered Mosaic camera sets.
Some are coadds of images from diverse epochs separated
by days, weeks or months. For the dither sequences, it makes
sense to simply construct a DATE-OBS from the weighted
average of the individual dates (and times). For the coadds
covering much longer timescales, this is less desirable.

Is there a de facto FITS standard for a keyword (something
like DATE-EFF) which reflects a date and time of mid-epoch?

Comments about the desirability of such?

Rob Seaman
NOAO Science Archive


I would say that an effective date would be meaningless; consider
a supernova that was peaking during the first frame, it might show
up in the final mosaic but not be related to DATE-EFF. The only
sure way would be to include a table of all the components; but
in the case of normal single-exposure frames, in many observing
systems DATE-OBS refers to the moment the shutter opens, and
hence in a composite could logically be set to the DATE-OBS
of the first component frame. With a careful explanatory comment...

Pete.