docs: def toGMST(dt=None):
      """Converts the given Python datetime or Julian date (float) to
      Greenwich Mean Sidereal Time (GMST) (in radians) using the formula
      from D.A. Vallado (2004).
  
      See:
  
          D.A. Vallado, Fundamentals of Astrodynamics and Applications, p. 192
          http://books.google.com/books?id=PJLlWzMBKjkC&lpg=PA956&vq=192&pg=PA192
      """
      if dt is None or type(dt) is datetime.datetime:
          jd = toJulian(dt)
      else:
          jd = dt
  
      tUT1  = (jd - 2451545.0) / 36525.0
      gmst  = 67310.54841 + (876600 * 3600 + 8640184.812866) * tUT1
      gmst += 0.093104 * tUT1**2
      gmst -= 6.2e-6   * tUT1**3
  
      # Convert from seconds to degrees, i.e.
      # 86400 seconds / 360 degrees = 240 seconds / degree
      gmst /= 240.
  
      # Convert to radians
      gmst  = math.radians(gmst) % TwoPi
  
      if gmst < 0:
          gmst += TwoPi
  
      return gmst