Some presenters may also be an actor, model, singer, comedian or other profession. Others may be experts on certain things. These include scientists or politicians They work as presenters for a programme about what they are an expert at. For instance, Carl Sagan, an astronomer was the host of "", a television series that dealt understanding the universe. Some television presenters are celebrities who have made their name in one area and use their fame to work in other areas. Examples of this include British comedian Michael Palin who now presents programmes about travel (such as ""), and Alan Alda, who has presented "Scientific American Frontiers".