New Year's Day is observed on January 1, the first day of the year on the modern Gregorian calendar as well as the Julian calendar used in ancient Rome. With most countries using the Gregorian calendar as their main calendar, New Year's Day is the closest thing to being the world's only truly global public holiday, often celebrated with fireworks at the stroke of midnight as the new year starts. January 1 on the Julian calendar currently corresponds to January 14 on the Gregorian calendar, and it is on that date that followers of some of the Eastern Orthodox churches celebrate the New Year. New Year's Day is a postal holiday in the United States.^[1]

The Romans dedicated this day to Janus, the god of gates, doors, and beginnings. After Julius Caesar reformed the calendar in 46 BC and was subsequently murdered, the Roman Senate voted to deify him on the 1st January 42 BC ^[2] in honor of his life and his institution of the new rationalized calendar.^[3] The month originally owes its name to the deity Janus, who had two faces, one looking forward and the other looking backward. This suggests that New Year's celebrations are founded on pagan traditions. Some have suggested this occurred in 153 BC, when it was stipulated that the two annual consuls (after whose names the years were identified) entered into office on that day, though no consensus exists on the matter.^[4] Dates in March, coinciding with the spring equinox, or commemorating the Annunciation of Jesus, along with a variety of Christian feast dates were used throughout the Middle Ages, though calendars often continued to display the months in columns running from January to December.^{[citation needed]}

Square Root Day is an unofficial holiday celebrated on days when both the day of the month and the month are the square root of the last two digits of the year.^[1] For example, the last Square Root Day was March 3, 2009 (3/3/09), and the next Square Root Day will be April 4, 2016 (4/4/16). The final Square Root Day of the century will occur on September 9, 2081. Square Root Days fall upon the same nine dates each century.

Ron Gordon, a Redwood City, California high school teacher, created the first Square Root Day for September 9, 1981 (9/9/81). Gordon remains the holiday's publicist, sending news releases to world media outlets.^[2] Gordon's daughter set up a Facebook group where people can share how they were celebrating the day.^[3]