Units of Time
The Hebrew calendar is a lunar calendar based on 19-year cycles - each day is divided into 24 hours, which are then divided into 1080 parts (or "halakhim").
A month is defined as the period from one new moon to the next, corresponding to the astronomical definition of a siderial month. The length of a month is taken to be 29 days, 12 hours, and 793 halakhim.
Types of Years
A year in the Hebrew calendar is normally twelve months: Tishrei, Cheshvan, Kislev, Tevet, Sh'vat, Adar, Nisan, Iyar, Sivan, Tammuz, Av, and Elul. An extra month (Adar is replaced with Adar I and Adar II) is included seven of every nineteen years (years 3, 6, 8, 11, 14, 17, and 19) to maintain accuracy. Every 19-year cycle thus contains 235 months.
The Hebrew Calendar is an amazing mathematical achievement – to learn more about how it works, an in-depth scholarly analysis may be viewed here. Note that you will need a copy of the Adobe Acrobat reader to view this document.
To convert from Gregorian (American-standard) calendar dates to Hebrew, visit http://www.hebcal.com/converter/
For a comprehensive (and beautifully rendered!) moonphase and tide predictor, click here
If you would like to see what Torah and Haftarah portion you chanted (or will chant) at your Bar/Bat/B'not Mitzvah, click here. If you would like to see how time is represented in virtually every other calendar system still in use, click here.
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