A nuclear weapons test is an experiment during which a nuclear, or atomic, weapon is exploded. The purpose is to analyze many of its different effects on, above, below or within the surrounding land and atmosphere that the device has been detonated. Countries throughout the world that have nuclear weapons are known as nuclear weapon states, and often the purpose of their nuclear weapons test is simply to let the rest of the world know that they have these powerful weapons at their disposal. Tests have been carried out by many countries throughout the world, including the United States, France, the Soviet Union, Britain, and others.
Nuclear weapons are explosive devices that can be deployed in a variety of ways. They create a massively powerful explosion either through fission and fusion combined, or just through fission, with both being known as nuclear reactions. The main reason to test a bomb is to see whether or not it works. Additional data that is collected in a nuclear weapons test can be used to study many aspects of the explosion as well as its impact on the surrounding environment. For instance, structures have been built on a nuclear weapons test site to examine how they are affected by the detonated bomb at various distances from the point of impact.
The very first nuclear weapon to be tested was done so on 16 July 1945 by the United States, in an experiment referred to as Trinity. The tested bomb was exploded in New Mexico, and was the same design as the one nicknamed Fat Man that was exploded over Nagasaki, Japan on 9 August 1945 near the end of World War II. Scientists who were involved with Trinity determined that the weapon needed to be tested before its actual use because of concerns that an untested nuclear device may not explode as planned.
Three different varieties of tests exist: underground, underwater and atmospheric. While some tests are done to see what the impact is on these environments, more often a nuclear weapons test is done underground in order to minimize atmospheric impact due to nuclear fallout, which is when radioactive debris falls back to earth from the atmosphere after the explosion. Errors in judgment of weather conditions or the power of a particular bomb can create major problems when conducting atmospheric tests.
Because of all of these issues, some nuclear weapon states and many who do not have nuclear capabilities have agreed to ban nuclear tests altogether, an action that was adopted by many countries in 1996. A few more tests were done in 1998 by India and Pakistan before they stopped their own testing programs. The most recent nuclear weapons test by any country was claimed by North Korea in 2009, which was supposedly and underground test. This can be construed as an attempt by the country to declare themselves a threat to surrounding countries as well as the rest of the world.