New Year's Day, among ancient peoples the first day of the year frequently corresponded to the vernal or autumnal equinox, or to the summer or winter solstice. In the Middle Ages it was celebrated among Christians usually on Mar. 25. After the adoption of the Gregorian calendar that began in 1582, the day was observed on the first of January. The Jewish New Year is the first day of Tishri, which falls some time in September or in early October. The Chinese New Year (between Jan. 10 and Feb. 19 of the Gregorian calendar) is the most important of their festivals. The Muslim New Year falls on the first day of Muharram.