This year marks the centennial of Niels Bohr’s model of the hydrogen atom: an electron in orbit around a proton, much like a planet around a star.  Bohr’s model became the basis for a revolution that transformed astronomy in the 20th Century.

The Ask An Expert lecture series at the National Mall building is presented every Wednesday at noon. A Museum staff member talks to the public about the history, collection, or personalities related to a specific artifact or exhibition in the Museum.