def register_classes():
    """Register these classes with the `LinkFactory` """
    Gtlink_exphpsun.register_class()
    Gtlink_suntemp.register_class()
    Gtexphpsun_SG.register_class()
    Gtsuntemp_SG.register_class()
    SunMoonChain.register_class()
Register these classes with the `LinkFactory`