Twenty-seven years ago today, on January 28, 1986, the Space Shuttle Challenger exploded during its 10th flight mission (STS-51-L), just 73 seconds after liftoff. The mission was originally scheduled to begin on January 22, 1986, but it had to be rescheduled several times before the Challenger finally departed from Kennedy Space Center in Florida on Jan. 28. After the failure of an O-ring seal on one of the shuttle's Solid Rocket Boosters, the vessel burst into flames and exploded. The tragic events were captured during a live broadcast, and all seven crew members lost their lives.  

The seven crew members aboard the Challenger Shuttle seen from left: Sharon Christa McAuliffe, Gregory Jarvis, Judith A. Resnik, Francis R. (Dick) Scobee, Ronald E. McNair, Mike J. Smith, and Ellison S. Onizuka. (NASA)

This, the 25th flight of the American Space Shuttle program, was a highly publicized affair because it was the first time a non-government civilian — schoolteacher Christa McAuliffe — was welcomed aboard a space shuttle. The Teacher in Space Program, which President Ronald Reagan first announced in 1984, was organized by NASA to get students and teachers engaged in the wonders of space exploration. After McAuliffe's death, the program was canceled in 1990. 

Sharon Christa McAuliffe: September 2, 1948 - January 28, 1986 (NASA)

On the morning of the Challenger explosion, President Reagan was preparing for a pre-State of the Union luncheon when he learned about the tragedy. Huddled around a TV set, Reagan and members of his senior staff watch a replay of the accident. 

(AP Photo/Craig Fujii)

At 5 p.m. from the Oval Office, the president addressed the nation:

Ladies and gentlemen, I'd planned to speak to you tonight to report on the state of the union, but the events of earlier today have led me to change those plans. Today is a day for mourning and remembering.