The Vanderbilt Museum’s elegant Spanish-Revival mansion is the former home of William Kissam Vanderbilt II, great grandson of Commodore Cornelius. The 43-acre estate, listed on the National Register of Historic Places, overlooks Northport Bay and the L.I. Sound. Visitors take guided mansion tours, or may explore on their own the museum’s galleries of marine life, natural history and cultural artifacts, as well as its wild-animal habitats and dioramas. The Vanderbilt’s, Charles and Helen Reichert Planetarium is a state-of-the-art, 147-seat facility that features educational and entertainment shows. Recently renovated, the planetarium is one of the largest and most advanced in the United States. In addition to its 60-foot domed theater, where some shows recreate celestial events, the planetarium has an Observatory with a professional-grade, 16-inch Meade reflecting telescope through which visitors can scan the real sky on clear evenings. During the day, visitors can view the sun safely through a new Lunt hydrogen-alpha solar telescope.