How to use Python's Astropy library to manipulate FITS files

How to use Python's Astropy library to manipulate FITS files

1. Import the relevant module and open a FITS file:

from astropy.io import fits
hdul = fits.open('file.fits')

2. Display file content information:

hdul.info()

3. Accessing individual Header/Data Units (HDUs):

hdu = hdul[0]  # Access the first HDU

4. Access header and data from the HDU:

header = hdu.header
data = hdu.data

5. Modifying the data and header:

hdu.data = hdu.data * 2  # Multiply all data by 2
hdu.header['OBJECT'] = 'New_Object'  # Modify a header value

6. Access a specific keyword from the header:

object_name = header['OBJECT']  # Access a specific keyword

7. Add a new keyword to the header:

header['NEWKEY'] = (42, 'Demo keyword')  # Add a new keyword with a comment

8. Delete a keyword from the header:

del header['NEWKEY']  # Delete the keyword

9. Iterate over all keywords in the header:

for keyword in header:
    print(header[keyword])

10. Create a new HDU with your data and header:

from astropy.io.fits import PrimaryHDU
new_hdu = PrimaryHDU(data=hdu.data, header=hdu.header)

11. Append new HDU to the HDU list:

hdul.append(new_hdu)

12. Save the changes to a new FITS file:

hdul.writeto('newfile.fits', overwrite=True)

The overwrite=True argument is used to overwrite the output file if it already exists.

13. Slice the data (useful for large datasets):

Astropy supports slicing of FITS files without loading the entire file into memory:

slice = hdul[0].section[10:20, 10:20]  # Extract a 10x10 slice from the image

14. Close the FITS file:

hdul.close()