((DON"T expect Smithsonian museums, including National Zoo, to be always open))
https://www.si.edu/newsdesk/releases/smithsonian-announces-modified-schedule-museums-and-national-zoo-starting-tuesday
Smithsonian museums in the Washington, D.C., area and the National Zoo will adopt a new schedule starting Tuesday, Jan. 18, until further notice.
(snip)
Starting Tuesday, Jan. 18, the Steven F. Udvar-Hazy Center in Chantilly, Virginia, and the Smithsonian Institution Building (The Castle) will be open seven days a week. The National Museum of Natural History, the National Museum of American History, the National Museum of African American History and Culture will be open five days a week. Other museums in Washington and the National Zoo will adopt a ThursdaySunday schedule. The National Air and Space Museum on the National Mall, the National Postal Museum and the Anacostia Community Museum will be closed to the public until further notice.
This modified schedule allows the Smithsonian to continue to reposition key staff across its museums as needed while offering the public more opportunities to visit its museums.