Another good reason to follow the National Archives on Twitter, Tumblr and other media: Great updates.
Like this one on the explosive arrival of the Atomic Age:

Trinity atomic device “Jumbo” being positioned at White Sands, New Mexico – National Archives
Atomic Age Begins
On July 16, 1945 the United States tested a nuclear device, code named “Trinity”, for the first time in White Sands Proving Ground, New Mexico.
Left: [“Jumbo” atomic device being positioned for “Trinity” test at Alamogordo, New Mexico.], 1945
Right: [“Trinity” explosion], 07/16/1945
Source: research.archives.gov

Rare color photograph of the first nuclear test at Trinity site, July 16, 1945. Blurriness is in the original photograph (done when color photography was still fairly new). (Photo credit: Wikipedia)

This is based on an earlier post, and is mostly an encore post.
Spread the word; friends don't allow friends to repeat history.