NASA established the Day of Remembrance to honor those who have died in America’s space program. The day focuses on those who died in three NASA space tragedies: the Apollo 1 fire on January 27, 1967; the Shuttle Challenger disaster of January 28, 1986; and the Shuttle Columbia tragedy of February 1, 2003. The day also remembers NASA employees who died in training and maintenance accidents. NASA headquarters observes the day with a roll call of all those who have died. At Cape Canaveral in Florida, a moment of silence is observed at noon.
Source: The Free Dictionary