Whether or not you believe that aliens have visited Earth, UFOs are a fascinating concept. There have been reported UFO sightings all over the world since pretty much the time when people started to keep written records. UFO doesn’t necessarily mean alien, it simply means Unidentified Flying Object, and many of these sightings have been explained as unusual weather phenomena or some form of modern technology. But many are still a mystery. World UFO Day celebrates the possibility that aliens have visited Earth. You can celebrate this holiday by visiting areas where reported sightings have happened or watching the sky to try to find your own UFO. There is some disagreement about when this holiday is celebrated. Some celebrate it on June 24, the day of the first reported UFO sighting in the US in 1947. But most sources, including World UFO Day’s official website report that it is celebrated on July 2nd, the date of the Roswell UFO sighting and alleged capture by the US government, one of the most famous UFO sightings in history.