For centuries, humans have been witnessing UFOs in the sky. What those objects actually were may never be known, but the vast quantity of reported sightings in the last 150 years is quite amazing.
Created back in 2005, this UFO Sightings KMZ file still seems to be the most comprehensive of its kind. The map was created by Poly9, who was acquired by Apple a few years ago and no one seems to have updated the file since then. However, the file contains thousands of sightings each with details on what was seen:
UFOmaps.com contains somewhat more recent information and uses a nice Google Maps interface to display it, but nothing past 2010 is in there.
The National UFO Reporting Center is very up to date, and their data was used in the original KMZ file, but they don’t seem to have any kind of geospatial solution in place to view the data.
There have also been a number of UFO sightings in Google Street View. Some are listed on UFOsearchonline.com and you can find a few others by searching for “UFO” in the Google Earth Hacks Street View database.
Whether you believe in true UFO sightings or not, Google Earth is a great platform from which to view the patterns of sightings and explore what people may or may not have seen.