You will be reminded that today is grim 20th anniversary marked by a special that began with four doomed flights, examined in the two hour documentary “9/11:Four Flights” (History, 8 p.m.). It’s followed by a collection of personal videos by eyewitnesses stitched together as “9/11: I Was There” (History, 10 p.m.). Also premiering tonight is “Surviving 9/11” (Discovery 8 p.m.). 

The Metropolitan Opera commemorates the date with a live performance of Verdi’s “Requiem,” hosted by ballerina Misty Copeland on “Great Performances” (PBS, 8 p.m., check local listings). 

Remembrances will proliferate through the day and replays of some of this week’s earlier documentaries such as “Return of the Taliban: A Vice Special Report” (Showtime, 8 p.m.), “9/11 Firehouse” (Discovery, 5 p.m.), “9/11: One Day in America: Told in Full” (National Geographic, 9 p.m.) and “Memory Box: Escoes of 9/11” (MSNBC, 10 p.m.).

 Also: the entirety of Spike Lee’s “NYC Epicenters 9/11 to 2021 1/2” (HBO, 4 p.m.) will play back-to-back, crowned by its final two hour episode at 10 p.m..

Sports dominates prime time again with Washington at Michigan (ABC, 8 p.m.) and Stanford at Southern California (Fox, 10:30 p.m.) in college football after the baseball of Yankees at Mets (Fox, 7:30 p.m.). Other games are listed below.

The 2020 Noel Coward adaptation “Blithe Spirit” (Showtime, 9 p.m.) with Dan Stevens, Leslie Mann and Judi Dench makes its premium cable debut.