Getting Time objects from FITS headers

[dstansby]

Description

Several entries in FITS headers indicate a time, e.g. DATE-OBS, DATE-BEG, DATE-END etc. For more information, see section 9, table 35 of the FITS standard: https://fits.gsfc.nasa.gov/standard40/fits_standard40aa-le.pdf

As far as I can tell, there is no simple way to get these out of an astropy.io.fits.Header object, and into a astropy.time.Time object. The best I have is

tsring = header['DATE-OBS']
scale = header['TIMESYS']
dtime = Time(tstring, scale=scale, format='fits')

It would be nice if there was a way for astropy to automatically apply the scale and any other necessary keywords, e.g. MJDREF. Perhaps a Header.get_time(key) method where key could be e.g. DATE-OBS would be helpful?

I would be happy to implement such a helper, but thought it would be best to first seek advice on whether this would be welcomed/what the API should be.

Additional context

There is #6676 already open, but I think that refers to times stored as data in columns as opposed to the header.

[saimn]

There is also #10073 about setting FITS headers with datetime or Time instances.

[mhvk]

Indeed, this would be great! I think it may be best to move discussion to #10073, and expand that to setting and getting. (I'll comment more there.)