ROSH HASHANAH (Jewish New Year - 5770): Starts today, September 18, at sundown

Rosh Hashanah (literally "head of the year) is a Jewish holiday commonly referred to as the "Jewish New Year."
---------The traditional Hebrew greeting on Rosh Hashanah is shana tova for "[a] good year", or shana tova umetukah for "[a] good and sweet year." Because Jews and the world are being judged by God for the coming year, a longer greeting translates as "may you be written and sealed for a good year" (ketiva ve-chatima tovah). It is customary that during the afternoon of the first day the practice of tashlikh is observed, in which prayers are recited near natural flowing water, and one's sins are symbolically cast into the water. Many also have the custom to throw bread or pebbles into the water, to symbolize the "casting off" of sins.
---------The Hebrew Bible defines Rosh Hashanah as a one-day observance, and since days in the Hebrew calendar begin at sundown, the beginning of Rosh Hashanah is at sundown at the end of 29 Elul. The rules of the Hebrew calendar are designed such that the first day of Rosh Hashanah will never occur on the first, fourth, or sixth days of the Jewish week[9] (ie Sunday, Wednesday or Friday).
Source: Wikipedia