Eight O'ahu museums will offer free admission to Smithsonian magazine readers and those who visit Smithsonian .com during the publication's fourth annual Museum Day on Sept. 27.

The participating museums are: Hawai'i State Art Museum, Manoa Heritage Center, Mission Houses Museum, Pacific Aviation Museum, Queen Emma Summer Palace, University of Hawai'i Art Gallery, Bishop Museum and Hawaii Maritime Center.

The event emulates the "open-door" policy of the Smithsonian Institution's Washington-based facilities and celebrates culture, learning and knowledge.

Nearly 900 museums and cultural institutions are participating this year across the nation and in Puerto Rico.

To participate, you'll need a Museum Day Admission Card. The card is available in the September issue of Smithsonian magazine, and a downloadable version is available at www.smithsonian.com/museumday.

Each card provides museum access to two people, and one admission card is permitted per household.