**Pi Day** is an unofficial holiday commemorating the mathematical constant π (pi). Pi Day is observed on March 14 (or 3/14 in *month/day* date format), since 3, 1 and 4 are the three most significant digits of π in the decimal form. In 2009, the United States House of Representatives supported the designation of Pi Day.

**Pi Approximation Day** is observed on July 22 (or 22/7 in *day/month* date format), since the fraction 22⁄_{7} is a common approximation of π.

Read more about Pi Day: History, Date Abstractions From π, Observance

### Famous quotes containing the word day:

“By *day* thy warning ringing bell to sound its notes,

By night thy silent signal lamps to swing.”

—Walt Whitman (1819–1892)