The Post Office recently announced a new stamp featuring the Civil War battle of Vicksburg. My first thought was Where's the UFO? That's not a normal reaction from a normal person. There supposedly was a large sphere hovering over this particular battle and an artillery battery stopped firing because everyone was gawking at the UFO.
Actually, there were quite a few UFO sightings during the 19th century, which was a clear sky era before powered flight had been perfected. I've actually given talks about this subject.