title: What does the format means in fits.Column()?
body: <p>I'm learning to create a fits file and I looked up in the astropy coumentation: <a href="https://docs.astropy.org/en/stable/io/fits/" rel="nofollow noreferrer">https://docs.astropy.org/en/stable/io/fits/</a>
  But I dud not understand what do <code>format='20A'</code> and <code>'E'</code> mean. And what does changing them imply to my fits file? The answer doesn't seem to be anywhere in the astropy documentation.</p>
  
  <p>That is the code from the documentation tutorial:</p>
  
  <pre><code>import numpy as np
  from astropy.io import fits
  
  a1 = np.array(['NGC1001', 'NGC1002', 'NGC1003'])
  a2 = np.array([11.1, 12.3, 15.2])
  col1 = fits.Column(name='target', format='20A', array=a1)
  col2 = fits.Column(name='V_mag', format='E', array=a2)
  
  cols = fits.ColDefs([col1, col2])
  
  hdu = fits.BinTableHDU.from_columns(cols)
  
  hdu.writeto('table3.fits')
  </code></pre>