Rosh Hashanah is the Jewish New Year feast and celebration.
The Jewish Calendar is a lunar calendar, therefor the dates of Rosh Hashanah and other Jewish holidays will vary according to the Gregorian Calendar (the standard calendar used in most of the world for politics, business and daily life.) In 2015 Rosh Hashanah begins at Sundown on September 13 and ends at nightfall of September 15.