fits header key 'date-obs' not preserved

[gica3618]

fits header key 'date-obs' not preserved

[richteague]

This all comes about from the _write_header function in io.py. I think my original intent was to have a very cleaned out header and just include the information that was needed, but perhaps it would just be easier to copy the old header and clean out the spectral coordinate stuff?

[gica3618]

Ok now I realised that this is actually a problem of CASA's imhead. If I check the headers with astropy, the 'date-obs' keyword is not there, which is fine. But reading the header with imhead, it says that 'date-obs' equals 1858/11/17/00:00:00. So imhead just seems to insert a default value if the keyword is not there. I guess I will have to talk to the CASA people about that...