On Tuesday, several memorials will be held around the city to honor those who lost their lives six years ago during the September 11 terrorist attacks—and at least one event will raise some serious questions about that day and its aftermath.

World Trade Center Site Memorial Ceremony and Remembrance
The official observance of the anniversary of 9/11 will take place at Zuccotti Park, adjacent to the World Trade Center site, starting at 8 a.m. Responders will read the names of the victims, while the "Tribute in Light"—two light beams that extend from the site—will also return at sundown. (Zuccotti Park, adjacent to the Trade Center site at Liberty Street between Broadway and Church St./Trinity Pl.)

Here Is New York: Remembering 9/11/01
This New York Historical Society exhibit features more than 1,300 photographs, recovered objects (including landing gear from one of the planes, doors from a fire truck and a crushed clock with the hands frozen at 9:04), and video and audio recordings of survivors, family members, recovery workers and more. (170 Central Park West between 76th and 77th Sts. Runs from Tue., Sept. 11, through Mon., Dec. 31. Free admission on Sept. 11)

Annual Floating Lanterns Ceremony
In a special ceremony, Rev. Nakagaki of the New York Buddhist Church will honor the lives of those who were lost, as well as provide "the light of hope for peace and harmony." From 6 p.m. to  9 p.m., the event is free and open to the public. (Pier 40 at West Houston St. and the Hudson River)

Music From Ground Zero: The Sixth Annual Rock Musical Memorial
Nonprofit organization Music From Ground Zero has been hosting this concert at The Knitting Factory on Sept. 11 for six years. The band on this night will consist of local musicians Tim Tuttle, Jeremy Slansky, Rich Lamb, Donna Kelly, Owen Yost, Jonathan Fritz, Mark Dann and Claudia Chopek. (74 Leonard St.; $12 at the door, $10 presale)

9/11 Truth: Ready for Mainstream
This gathering is composed of academics, architects, scientists, engineers, and retired military and intelligence professionals who believe the official account of 9/11 from the government does not represent the whole truth behind the events. A protest will take place at Ground Zero in the morning, while a screening of the documentary "9/11 Mysteries" will be shown at Union Square the following night at 7 p.m. (Ground Zero and Union Square Park)