Flags are flying at half-staff today, Sept. 11, across California and the United States for Patriot Day.

On Sept. 11, 2001, terrorists launched an attack on American soil, killing almost 3,000 people in New York City, Washington, D.C., and in a Pennsylvania field.

Patriot Day honors the memory of those victims and the first responders and service members who served after the attacks.

On Sept. 11, 2001, al-Qaida launched a series of terrorist attacks against the United States, killing almost 3,000 people.

Terrorists hijacked four passenger planes. Two planes crashed into two towers at the World Trade Center in New York City, and another crashed into the Pentagon outside Washington, D.C.

A fourth plane crashed into an empty field in Shanksville, Pennsylvania, after passengers tried to take control of the plane from hijackers before the plane was used to crash into another “important symbol of democracy and freedom.”

Why are flags flying at half-staff today, Sept. 11?

The U.S. flag should be flown at half-staff across the country at all governmental buildings today, Sept. 11, in observance of Patriot Day.

Is Patriot Day a federal holiday?

No. Patriot Day is not a federal holiday. Government offices will be open and mail will be delivered.

Observe a moment of silence at 8:46 a.m. ‘to honor the innocent victims’

Americans are encouraged to observe a moment of silence beginning at 8:46 a.m. to honor the victims who died as a result of the attacks.

Public law passed in US to designate Sept. 11 as Patriot Day

In December 2001, a law was passed to designate Sept. 11 as Patriot Day.

How to correctly fly your flag at half-staff

On days when the flag is flown at half-staff, it should first be raised to the top of the pole for an instant and then lowered to the half-staff position, according to the U.S. Flag Code.

Before lowering the flag, it should again be raised to the top before being lowered for the day.

Do flags fly at half-mast or half-staff?

On ships and at naval stations ashore, flags are flown at half-mast. On shore, flags are flown at half-staff.

This article originally appeared on Palm Springs Desert Sun: Flags at half-mast for 9/11 Patriot Day, Day of Service, Remembrance