def blue_hour_utc(self, direction, date, latitude, longitude, observer_elevation=0):
        """Returns the start and end times of the Blue Hour in the UTC timezone
        when the sun is traversing in the specified direction.

        This method uses the definition from PhotoPills i.e. the
        blue hour is when the sun is between 6 and 4 degrees below the horizon.

        :param direction:  Determines whether the time is for the sun rising or setting.
                           Use ``astral.SUN_RISING`` or ``astral.SUN_SETTING``.
        :type direction:   int
        :param date: The date for which to calculate the times.
        :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 the blue hour for
        :type observer_elevation:   int

        :return: A tuple of the UTC date and time at which the Blue Hour starts and ends.
        :rtype: (:class:`~datetime.datetime`, :class:`~datetime.datetime`)
        """

        if date is None:
            date = datetime.date.today()

        start = self.time_at_elevation_utc(-6, direction, date, latitude, longitude, observer_elevation)
        end = self.time_at_elevation_utc(-4, direction, date, latitude, longitude, observer_elevation)

        if direction == SUN_RISING:
            return start, end
        else:
            return end, start
Returns the start and end times of the Blue Hour in the UTC timezone
        when the sun is traversing in the specified direction.

        This method uses the definition from PhotoPills i.e. the
        blue hour is when the sun is between 6 and 4 degrees below the horizon.

        :param direction:  Determines whether the time is for the sun rising or setting.
                           Use ``astral.SUN_RISING`` or ``astral.SUN_SETTING``.
        :type direction:   int
        :param date: The date for which to calculate the times.
        :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 the blue hour for
        :type observer_elevation:   int

        :return: A tuple of the UTC date and time at which the Blue Hour starts and ends.
        :rtype: (:class:`~datetime.datetime`, :class:`~datetime.datetime`)