This little-known gem is part of The Carnegie Observatories, a venerable institution that's been around since 1904, when George Hale got the idea to hit up the Carnegie institute for the money.
The simple, classically-styled building pops up at 813 Santa Barbara Street, a residential side street off of Lake Avenue. If traffic never got tight on Lake you might not know it was there. Hey! You can observe them! They give tours! And they're having an open house November 16th.
The plaque dedicates the building to George Ellery Hale, the first director of the Observatory, and notes that the "building was erected in 1912. Myron Hunt, Architect." Mr. Hunt designed many of Pasadena's most beautiful homes including that of Henry E. Huntington (now a gallery of the Huntington Library), as well as such other southern California landmarks as Occidental College in Eagle Rock, Pasadena's Public Library and the Rose Bowl.
Here's a side door. The sign in the window says "no skateboarding." I picture guys and gals with Einstein hair, whipping their wheels off that porch and onto the sidewalk.