def twilightName(sunAlt):
    """
    Determine the type of twilight for a given altitude of the Sun.
    
    Definitions of twilight:
      - Solar altitude > 0    : day
      - Solar altitude <= 0   : civil twilight
      - Solar altitude <= -6  : nautical twilight
      - Solar altitude <= -12 : astronomical twilight
      - Solar altitude <= -18 : night

    Parameters
    ----------
    sunAlt : float
        Altitude of the Sun in degrees.
         
    Returns
    -------
    Twilight flag : string, {"day", "civil twilight", "nautical twilight", "astron. twilight", "night"}
        Specifies the type of twilight corresponding to the
        given solar altitude.
         
        The twilight flag is either "day", "civil twilight", "nautical twilight",
        "astron. twilight", or "night".
  """
    if sunAlt <= -18.0:
        return 'night'
    if sunAlt <= -12.0:
        return 'astron. twilight'
    if sunAlt <= -6.0:
        return 'nautical twilight'
    if sunAlt <= 0.0:
        return 'civil twilight'
    return 'day'
