I’m not sure of an adequate way to celebrate, but, nevertheless, we should celebrate.
A Square Root Day is when the first two numbers in the date are the same and when multiplied they equal the final two or three numbers of the year. In this case, it’s 3-3-09. 3 x 3 = 09. Or the square-root of 9 is 3. The next Square Root Day is April 4th, 2016.