title: AstroPy SkyCoord extremely slow, how to resovle it?
body: <p>I am using AstroPy SkyCoord to do conversion from equatorial coordinates to galactic coordinates with millions data, it is extremely slow. Anyone has idea to speed it up, otherwise it takes forever to run the whole dataset. The code is below:</p>
  
  <pre><code>from astropy import units as u
  from astropy.coordinates import SkyCoord
  import numpy as np
  
  ra1 = np.loadtxt('data.txt',usecols=(0,))
  dec1 = np.loadtxt('data.txt',usecols=(1,))
  size = len(ra1)
  for i in range(size):
      ra = ra1[i]
      dec = dec1[i]
      c = SkyCoord(ra*u.degree, dec*u.degree)
      cc = c.galactic
      b = cc.b.degree
      l = cc.l.degree
  </code></pre>