On Jan. 28, 1986, the Challenger Space Shuttle lifted off in a plume of smoke and fire from Kennedy Space Center in Florida, jetting through the sky toward space.
Just 73 seconds after takeoff, the space shuttle experienced a booster engine failure and exploded over the Atlantic Ocean off the coast of Cape Canaveral.
Two payload specialists and five astronauts died: Sharon "Christa" McAuliffe, Gregory Jarvis, Judith Resnik, Francis Scobee, Ronald McNair, Mike Smith, and Ellison Onizuka.
NASA later determined that a catastrophic failure to one of the shuttle's O-rings led to the explosion of the shuttle's fuel tank.
Pres. Ronald Regan, scheduled to give a State of the Union address that same day, addressed the nation instead on the day's events.
"We will never forget them, nor the last time we saw them, this morning, as they prepared for the journey and waved goodbye and 'slipped the surly bonds of earth' to 'touch the face of God," Reagan said to the country.
Today, NASA observes a Day of Remembrance for those lost on the Challenger, as well as for those who died in the Apollo 1 and Columbia accidents.
— NASA (@NASA) January 28, 2017
McAuliffe, a New Hampshire high school teacher, was one of thousands of teachers who competed in NASA's "Teacher in Space" program, ultimately winning the opportunity to be the first teacher in space.
One of those teachers who could have been in McAuliffe's seat is former La Jolla High School teacher Gloria McMillan.
McMillian was in attendance that day in Florida, alongside other teachers who had competed for a seat on the shuttle. What was supposed to be a day of celebration for them, ended in tragedy.
The next day, McMillian was back at work with the same notion thousands of other teachers across the country had: It could have been me.
"As soon as I came in, there were hugs all around for me," McMillan told the San Diego Union-Tribune (http://bit.ly/2jpQCDw) in 2013. "When you’re grieving, work is a wonderful antidote. It’s absolutely medicinal.
"You know, I asked my students, ‘How can we honor the Challenger seven?’ And they came up with things that they wanted to do, and classrooms across the country did."
Since that day, many of McAuliffe's former students have gone on to become teachers, inspired by the lessons and acts of their former teacher.