When do the Holidays begin?
All Jewish Holidays begin the evening before the date specified. This is because the Jewish day actually begins at sundown on the previous night. Sometimes, for clarity, the Erev Holiday is also included.

When does Shabbat begin?
Shabbat begins 18 minutes before sundown on Friday night.

What does CH''M mean?
CH''M is an abbreviation for Chol Ha-Mo'ed. Chol Ha-Mo'ed are the intermediate days of Passover and Sukkot, when work is permitted.

What is Havdalah (or, When does Shabbat end)?
Shabbat ends after sundown on Saturday night when there are three stars visible. Depending on latitude and longitude, this is usually between 42 and 72 minutes after sundown.

How accurate are candle lighting times?
This calendar computes sunset based on an algorithm by the U.S. Naval Observatory (USNO). The USNO claims accuracy within 2 minutes except at extreme northern or southern latitudes. Comparison to local NWS charts for sunrise and sunset shows that with the double precision calculations, the charts produced by this program are no more than 1 minute removed from those charts in lattitudes lower than 41 degrees. Candle lighting times agree with those on popular calendars also to the 1 minute accuracy.