Answer:
The Trinity test was the first test of a nuclear weapon by the United States. It took place on July 16, 1945. It was the first explosion in the history of a weapon of this type.
At the time of the detonation, the surrounding mountains were illuminated for one to two seconds. The observed colors of the illumination varied from purple to green, and finally to white. The explosion took 40 seconds to reach the observers and the shock wave could be felt 160 kilometers away. The mushroom cloud reached 12 kilometers.
(The result of the Trinity Test led to the people involved conclude that it is a very dangerous weapon.)