关于UFO的资料An unidentified flying object, or UFO, is any real o

关于UFO的资料
An unidentified flying object, or UFO, is any real or apparent flying object which cannot be identified by the observer and which remains unidentified after investigation. The term flying saucer is also sometimes used, although the two terms are not genuinely interchangeable.
Reports of unusual aerial phenomena date back to ancient times (see Ancient astronaut theories), but modern reports and first official investigations began during World War II with sightings of so-called foo fighters by Allied airplane crews and in 1946 with widespread sightings of European ghost rockets. UFO reports became even more common after the first widely publicized United States sighting in 1947. Many tens of thousands of UFO reports have since been made worldwide. [1] Many sightings may remain unreported due to fear of public ridicule because of the social stigma surrounding the subject of UFOs and because most nations lack any officially sanctioned authority to receive and evaluate UFO reports.
Once a UFO is identified as a known object (for example an aircraft or weather balloon), it ceases to be classified as a UFO and is reclassified as an identified object. 这段话什么意思？急求！！！！！!!!!！！！！谢谢

UFO全称为不明飞行物，也称飞碟（unidentified flying object，简称UFO）是指不明来历、不明空间、不明结构、不明性质，但又漂浮、飞行在空中的物体。一些人相信它是来自其他行星的太空船，有些人则认为UFO属于自然现象。20世纪40年代开始，美国上空发现碟状飞行物，当时称为“飞碟，这是当代对不明飞行物的兴趣的开端，后来人们着眼于世界各地的不明飞行物报告，但至今尚未发现确实可信的证据。许多不明飞行物照片经专家鉴定为骗局，有的则被认为是球状闪电，但始终有部分发现根据现存科学知识无法解释。