September 11th is Patriot Day in the U.S.
On this day in 2001, terrorists hijacked four planes. They flew two into the World Trade Center in New York. They flew another into the Pentagon, the U.S. military headquarters in Washington, DC. The fourth plane crashed into the ground. (Passengers on it fought back.)
In all, 2,974 people were killed.
On Patriot Day, Americans are asked to remember those who died.
Rosh Hashanah, the Jewish New Year's Day, begins at sunset on September 13th this year.
It is a time for Jews to think about the past year and the year ahead. They think about things they have done wrong in the past year. They also hope the next year will be good.