Khizr and Ghazala Khan, who lost their son, U.S. Army Capt. Humayun Khan, in service during the War in Iraq, offered a strong rebuke to Republican presidential nominee Donald Trump's rhetoric in attacking Muslim-Americans.

Still, Trump dug in his heels by belittling the couple after their prime-time speech at the Democratic National Convention, sparking a major flash point in the presidential campaign that raised questions over Trump's temperament in addressing the grieving parents of a fallen American soldier. 

Here's how the three sites of the attack — New York, Washington, D.C., and Shanksville, Pennsylvania — and others will remember the fallen. For memorials around the world, go here.

Sept. 11

"Tribute in Light" (New York)

The Municipal Art Society of New York presented this public art tribute for 10 years. Today, the twin beams of blue light emanating from Ground Zero are under the direction of the National September 11 Memorial & Museum. The 88 7,000-watt xenon light bulbs, arranged and positioned to recall the Twin Towers, will shine from dusk to dawn the next day. They're visible from a 60-mile radius, and reach 4 miles into the sky.

National Day of Service and Remembrance (Anywhere)

Visit 911day.org for opportunities in your community.

Sept. 12

"Rendering the Unthinkable" Exhibit (New York)

The 9/11 Memorial opens an exhibit of artistic reactions to the deadly attacks, collecting the work of 13 artists. For more information, go here.