This is the earliest that Rosh Hashanah has appeared on the Gregorian Calendar since 1899. Later this year, Chanukah and Thanksgiving will occur on the same day for the first time in history. With the nuances of the calendars, this will not happen again for 77,789 years.
It will be 5774 on the Jewish calendar which is a leap year. Since the Jewish calendar is lunisolar, a calendar whose date indicates both the moon phase and the time of the solar year, a leap year adds one month to the calendar. Adar I will begin on February 1 and last for 29 days. All Adar holidays, such as Purim, occur in Adar II.