On the night of Dec. 23, a flight crew was flying back to Fort Lauderdale in an empty jet, high over the Bahamas, when they spotted a glowing, spherical object darting about too much to be a weather balloon. The aerospace world is full of flying machines that we all recognize, but sometimes, people see things in the sky that defy explanation. “It started as white and then it just got green and almost like an electric, some type of energy around it,” said Cassandra Martin, a flight attendant for Surjet, a private air service. On the night of Dec....