code: def declinationRotationMatrix(theta_deg):
      
  
      ct = np.cos(np.radians(theta_deg))
      st = np.sin(np.radians(theta_deg))
  
      mat = np.zeros((3,3))
  
      mat[0,0] = ct
      mat[0,2] = -st
      mat[1,1] = 1
      mat[2,0] = st
      mat[2,2] = ct
  
      return mat
docs: Construct the rotation matrix for a rotation of the declination
      coords (i.e around the axis of ra=90, dec=0)
  
      Taken from Section 3.3 of Arfken and Weber (Eqn 3.91)
      Modfied the signs of the sines so that a rotation of the zenith
      vector by 90 degrees ends up at ra, dec = 0,0