Happy Constitution Day! The federal observance is trending but many are unsure about its specifics.
Formerly known as Citizenship Day, the holiday marks the formal adoption of the U.S. Constitution and recognizes those who have become U.S. citizens.
It's observed on Sept. 17— adjacent weekdays in case the day falls on a weekend as it does this year. That's the date in 1787 when the Constitution was signed by 39 statesmen.