In 1986, the Space Shuttle Challenger exploded 73 seconds after liftoff, killing all seven crew members.
The crew of Space Shuttle Challenger consisted of Mission Commander Francis R. Scobee; Pilot Michael J. Smith; Payload Specialists Gregory B. Jarvis and Christa McAuliffe; Mission Specialists Judith A. Resnik, Ellison S. Onizuka and Ronald E. McNair.
Read more at http://www.aerospaceguide.net/spaceshuttle/challenger_disaster.html
In 1613, Galileo may have unknowingly viewed undiscovered planet Neptune.
According to University of Melbourne physicist David Jamieson,
“If this is correct Galileo observed Neptune 234 years before its official discovery.”