EDITORIAL: Mark Sunday on your calendar

Nightmares are supposed to fade.

This one doesn’t. Nor must it ever.

Sunday marks the 21st anniversary — hard as that is to believe — of the vile acts of terrorism that briefly brought our nation to its knees. Here’s the precise timeline, as noted by the nonprofit Wreaths Across America:

Tuesday, Sept. 11, 2001, 8:46 a.m. (Eastern time): Five hijackers took control of American Airlines Flight 11 and flew it into the heart of New York City and the northern facade of the World Trade Center's North Tower (1 WTC).

At 9:03 a.m., five hijackers flew United Airlines Flight 175 into the southern facade of the South Tower (2 WTC).

At 9:37 a.m., five hijackers flew American Airlines Flight 77 into the western facade of the Pentagon in Arlington County, Va.

At 10:03 a.m., four hijackers crashed United Airlines Flight 93 into a field in Stonycreek Township near Shanksville, Pa.

There’s a reason we’re introducing you to an aspect of Wreaths Across America that you might not have known. The organization famous for spreading wreaths on graves of veterans every December is calling on Americans to participate in another patriotic activity.

This Sunday at 5:46 a.m. Pacific time (8:46 Eastern), head outside with an American flag and wave it.

If you’re really dedicated to the idea, coordinate with family and friends and find a public place to wave Old Glory. According to Wreaths Across America, ardent flag wavers should do their thing until 7:03 p.m. Pacific time, marking the duration between the first crash and the last.

We think this is a fine way to put our petty partisanships aside and join together to honor those who fell — and those who, 21 years ago Sunday, risked their lives to save others. From that tragedy, the American spirit came shining through.

We can't think of anything more worth remembering.