Astroart Forum

Hello,
Can you please confirm what is the timestamp when recording airmass in FITS headers?
I assume it is the beginning of the exposure?
Regards
Patrick

Hello, the airmass is calculated at mid-exposure.
Instead, DATE-OBS is always the start of exposure in the FITS standard, and mid-exposure is a calculated field, as: DATE-OBS + EXPOSURE/2.
Fabio.

Thank you.