A photograph of Robert H. Goddard with his rocket in his shop in Roswell, New Mexico, October 1935.
Image: marshamalinowski.com.

On this date in 1920, the Smithsonian Institution publishes Robert H. Goddard’s monograph A Method of Reaching Extreme Altitudes. Goddard’s work lays out the concept of using a multi-stage rocket for exploration of outer space and reaching the lunar surface, a concept which would later become fundamental to spaceflight. You can read Goddard’s treatise at the Smithsonian website here.