Smithsonian Secretary Wayne Clough announced Monday that the three most popular museums on the National Mall will stay open longer through the summer in an effort to boost revenue for their gift shops and restaurants, the AP reports. The National Museum of Natural History and National Air and Space Museum will stay open two hours later, until 7:30 p.m., and the National Museum of American History will stay open at least one hour later, every day this summer. The museums open at 10 a.m. and typically closed at the end of the work day. A spokesperson for the Smithsonian confirmed that the extended hours actually started on Mar. 28, and will last until at least Sept. 7, with a few exceptions. Consult the web sites of each museum for the most up to date operating hours.