<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def night_utc(self, date, latitude, longitude, observer_elevation=0):
 """Calculate night start and end times in the UTC timezone. Night is calculated to be between astronomical dusk on the date specified and astronomical dawn of the next day. :param date: Date to calculate for. :type date: :class:`datetime.date` :param latitude: Latitude - Northern latitudes should be positive :type latitude: float :param longitude: Longitude - Eastern longitudes should be positive :type longitude: float :param observer_elevation: Elevation in metres to calculate night for :type observer_elevation: int :return: A tuple of the UTC date and time at which night starts and ends. :rtype: (:class:`~datetime.datetime`, :class:`~datetime.datetime`) """


        start = self.dusk_utc(date, latitude, longitude, 18, observer_elevation)
        tomorrow = date + datetime.timedelta(days=1)
        end = self.dawn_utc(tomorrow, latitude, longitude, 18, observer_elevation)

        return start, end