Instrument of Surrender. Thus, September 2 became Victory over Japan Day according to President Harry Truman -- but, by this point, America had been celebrating since August 14 (August 15 in Japan) when Emperor Hirohito announced Japan's surrender over the radio.
V-J Day is a legal holiday (called Victory Day) in the State of Rhode Island.
If you're looking for something else to celebrate today, you have to look pretty hard. You might try National Blueberry Popsicle Day -- but a better alternative may be Bowling Shirt Day. Wear the loudest one you can and take the kids on a family outing this afternoon -- they'll be embarrassed for weeks.