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