Sony Electronics and Nielsen television research company collaborated on the study that ranked TV moments for their impact, not just by asking people whether they remembered watching them, but whether they can remember where they watched it and whether they talked about it with others.
The Sept. 11 attack, according to the study's measurement, was nearly twice as impactful as the second top-ranked moment - Hurricane Katrina in 2005.
The other biggest TV events, in order, were the 1995 verdict in the O.J. Simpson murder trial, the Challenger space shuttle explosion in 1986 and the death of Osama bin Laden last year, the survey found.
Television coverage of news events made the biggest difference in viewer's lives as opposed to entertainment events on television.
The Super Bowl is annually the most-watched TV event, with this year's game between the New York Giants and New England Patriots setting an all-time record with 111 million viewers, but the memories don't seem to linger.
The passage of time also had an effect on moments that were once thought to be unforgettable, including man's first moon landing in 1969.
Age also made a big difference in the survey. JFK's assassination was the second-most impactful TV event among people 55 and over, while for those between 18 and 34, it was the death of Osama bin Laden.
The study was based on an online questionnaire of 1,077 adults selected as a scientific sample among Nielsen's panel of people measured for television ratings. It was conducted between Feb. 15-17 of this year. List of TV's top 20 most memorable moments Sept. 11 attacks 2001 Hurricane Katrina - the levees break 2005 OJ Simpson murder verdict 1995 Challenger space shuttle disaster 1986 Death of Osama bin Laden 2011 OJ Simpson high-speed car chase 1994 Earthquake/tsunami in Japan 2011 Columbine school shooting 1999 BP oil spill in the Gulf of Mexico 2010 Funeral of Princess Diana 1997 Death of Whitney Houston 2012 Capture and execution of Saddam Hussein 2006 Barack Obama acceptance speech 2008 Prince William, Kate Middleton wedding 2011 Assassination of John F. Kennedy 1963 Oklahoma City bombing 1995 Bush/Gore election results 2000 Los Angeles riots/Rodney King beating 1992 Casey Anthony murder trial verdict 2011 Funeral of John F. Kennedy 1963