The National September 11 Memorial Museum opens Wednesday in a ceremony that will unfurl the National 9/11 flag on Memorial Plaza.

The historic banner, donated by the New York Says Thank You Foundation, will then be formally installed in the new museum's permanent collection.

In the event of rain, the ceremony will be moved inside.

Opening day tickets to the Museum are no longer available: They were snapped up within 36 hours after an announcement in March that Conde Nast would cover all first-day admissions, said Museum spokesman Anthony Guido.

General admission tickets for future visits -- which can be reserved at 911memorial.org -- cost $24, although group, senior, veteran and student discounts are available. Admission will be free to the public from 5 to 8 p.m. on Tuesdays.

The "Memoriam" exhibition in the new museum pays tribute to the 2,983 people killed in the two attacks on the World Trade Center. Another historical exhibition provides a narrative of 9/11 -- what led up to the horrific day, the impact of the attacks and how they continue to affect New York City and the world.