UFO, also known as UFO, refers to an object with unknown origin, space, structure and nature, but floating and flying in the air. Some people think it is a spaceship from other planets, while others think UFO is a natural phenomenon. In the 1940s, a saucer-shaped flying object was found over the United States, which was called "UFO" at that time. This is the beginning of contemporary people's interest in UFOs. Later, people focused on UFO reports around the world, but so far no credible evidence has been found. Many UFO photos are considered as scams by experts, and some are considered as spherical lightning, but some are always found to be unexplained according to existing scientific knowledge.

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