> Nuclear detonations show two characteristic light pulses. This double-pulse phenomenon is evident in the video of the “Harlem event,” a 1.2 megaton test that took place 13,645 feet above the Christmas Island area of the Pacific on June 12, 1962. The first pulse peaks almost immediately as the shockwave first forms (0:09 in the video). The brightness then decreases as the superheated air, which is opaque when heated to above 3,300 degrees Kelvin -- or 5,480.33 degrees Fahrenheit -- shields the light from inside the fireball (0:10 in the video). As the shockwave cools to below 3,300 Kelvin, the air becomes transparent and the hot gasses begin to show through, creating the second pulse (0:21 in the video).<p>This is so interesting. I've always noticed the iconic double flashing in nuclear detonations but I never knew why it happened.<p>> Software developed by LLNL computer scientist Jason Bender scans each frame of the films to automate the measurement process. Bender’s software notes the timestamp of both pulses of light, as well as the darkest frame between them. With this data, Spriggs can calculate the test’s yield.<p>Sounds like a fun project, writing algorithms to parse 50yr old classified films of nuclear detonations.