Short answers, pulled from the story.
Trinity took place at 5:29 a.m. Mountain War Time on the 16th of July 1945, in the Jornada del Muerto desert of New Mexico, on what was then the Alamogordo Bombing Range, renamed the White Sands Proving Ground one week before the test. The site is approximately 35 miles southeast of Socorro, New Mexico.
The plutonium bomb used a complex implosion design that could not be relied upon without testing. A simpler gun-type design was ruled out because plutonium produced in reactors contained plutonium-240, an impurity that caused premature detonation and a much smaller explosion. The uranium gun-type bomb, Little Boy, was so straightforward that it was dropped on Hiroshima without any prior test.
The Trinity test released an energy equivalent to approximately 21,000 tons of TNT in the official estimate, with a 2021 reanalysis putting the yield at 24,800 tons of TNT equivalent, plus or minus 2,000 tons. The blast was felt over 100 miles away, and the mushroom cloud reached a height of 7.5 miles.
Kenneth Bainbridge, a professor of physics at Harvard University, planned and directed the Trinity test, working under explosives expert George Kistiakowsky. The test was part of the Manhattan Project, led overall by Brigadier General Leslie R. Groves, Jr., with J. Robert Oppenheimer directing the Los Alamos Laboratory.
The code name Trinity was assigned by J. Robert Oppenheimer, the director of the Los Alamos Laboratory. In a 1962 letter to Groves, Oppenheimer explained that the name was inspired by the poetry of John Donne, specifically Donne's devotional poem opening "Batter my heart, three person'd God." Oppenheimer also referenced a Donne poem linking death and resurrection.
The test was conducted without evacuating nearby residents, and fallout settled as far as 30 miles away on Chupadera Mesa, causing beta burns and hair loss in local livestock. A 2020 dose reconstruction by the National Cancer Institute identified five New Mexico counties with significant contamination: Guadalupe, Lincoln, San Miguel, Socorro, and Torrance. New Mexico residents were excluded from the 1990 Radiation Exposure Compensation Act, and efforts to include them continued in Congress through 2024.