New Year's is the celebration of New Year's Eve to New Year's Day. It is the transition, from the old year, to the new year in the Gregorian calendar observed in the Western Hemisphere. The observance spans 2 days (48 hours). The time is also known as Old Year's Day or Saint Sylvester's Day, in many countries. Is the evening or the entire day of the last day of the year, 31 December. The last day of the year is commonly referred to as “New Year's Eve”.