def check(self, orb):
        """Method that check whether or not the listener is triggered

        Args:
            orb (Orbit):

        Return:
            bool: True if there is a zero-crossing for the parameter watched by the listener
        """

        return self.prev is not None and np.sign(self(orb)) != np.sign(self(self.prev))
Method that check whether or not the listener is triggered

        Args:
            orb (Orbit):

        Return:
            bool: True if there is a zero-crossing for the parameter watched by the listener