But we are still left with a percentage that remain as a mystery. Some, of course, are simply hoaxes, intentionally designed to deceive. Some are later identified as natural phenomenon Many of the mysterious sightings in the sky that people past ages have encountered can possibly be explained by such things as aurora's, fireballs, flocks of birds. Probably one of the most notorious things to fall into this category is the planet Venus. Other sightings can be explained as airships, searchlights, and even laser-light shows at rock concerts.
Military aircraft is another explanation.
There is mounting evidence that new generations of remarkable military aircraft have been regularly misconceived as UFOs before the existence of their technology is officially confirmed. For example, reports of triangular UFOs in Belgium between 1989 and 1991 are now widely believed to have been operations by American stealth jets. This would also be confirmed by the fact that a lot of UFOs are sighted near secret military bases. However, there are a percentage which are simply unexplained. Many astronomers and physicists believe that UFOs and their occupants do not come from outer space.