docs: def field_elongation(ra, dec, date):
      """
      For a given field, calculate the solar elongation at the given date.
      :param ra: field's right ascension. unit="h"   format="RAh:RAm:RAs"
      :param dec: field's declination. degrees
      :param date: date at which to calculate elongation
      :return: elongation from the Sun in degrees
      """
      sun = ephem.Sun()
      sun.compute(date)
      sep = ephem.separation((ra, dec), sun)
      retval = 180. - math.degrees(sep)
  
      return retval