The basis of the Jewish calendar is the lunar month, which is approximately twenty-nine and a half days, the period of time in which the moon circles the earth once. The lunar year consists of 354 days, 12 hours, 44 minutes, and 31 seconds. The solar year contains 365 1/4 days. There is a difference of about eleven days between the Jewish lunar year and the secular solar year. It is necessary to add an intercalary month, or leap month, seven times in 19 years, in order that the Jewish Holy days may be observed at the proper seasons.

THE DAY— Ha-Yom, the Jewish day, is reckoned from sunset to sunset. Genesis 1:5 tells us that when God had finished His first day's work He announced "And it was evening and morning, one day." In Leviticus 23:32 we again read, "From even unto even shall ye observe your Sabbaths." The Jewish day is divided into three divisions, each part having its appropriate service as established in Temple times: Evening - Erev - Maariv Service; Morning - Boker - Shacharith Service; Afternoon - Tzaharaim - Minchah Service. The days of the week do not possess names, they are known by their number, as Yom Rishon - FIRST DAY, Yom Sheni - SECOND DAY, and so on, with the exception of the seventh day which has a name and is called the Shabbat. The word SHABBAT is associated with God’s act of finishing the creation of the world in six days and sanctifying the seventh day as a day to worship Him: “And on the seventh day God ended His work which He had made; and He Shabbat on the seventh day from all His work which He had made. And God blessed the seventh day, and sanctified it” (Genesis 2:1). In Isaiah 58:13, God is further explaining what Shabbat means: "If you restrain your foot because of the Shabbat, from pursuing your own pleasures on My holy day; and call the Shabbat a delight, the holy day of the Lord honorable; and shall honor it, not doing your own ways, nor pursuing your own pleasures, nor speaking of vain matters; then you shall delight yourself in the Lord; and I will cause you to ride upon the high places of the earth, and feed you with the heritage of Jacob your father."

THE WEEK— The seven days of the week are called SHEVUAH. From Shabbat to Shabbat constituted a week. The week is totally an abstract Jewish concept taken from the biblical account of creation. There is no celestial observance that can determine the passing of the week. The new week begins immediately after the HAVDALAH PRAYER on Saturday night. The end of the week is termed MOTZEIE SHABBAT - THE GOING OUT OF THE SHABBAT.

THE MONTH— The Hebrew name for month is CHODESH - which means RENEWAL and commences with the reappearance or renewal of the moon. The Jewish lunar month consists of twenty-nine days, twelve hours, forty-four minutes, and three and one-half seconds, or approximately twenty-nine and one-half days. For calendar purposes the months alternate between twenty-nine and thirty days. A month of thirty days is called MALAIM - FULL. A month of twenty-nine days is called CHASARIM - DEFICIENT.

The Beginning of Months and the New Year - Exodus 12:2 tells us that "this month (the month of Nisan or Aviv) shall be unto you the beginning of months." It is determined by the conjunction of the moon with the sun that forms the Vernal Equinox in the spring time. In Hebrew this particular period is called TEKUFOTH NISAN - THE CYCLE or PERIOD OF NISAN. The "Beginning of Months" should not be confused with Rosh HaShanah, the New Year, which occurs in the fall of the year on the first day of the month of Tishrei. The beginning of months is used to reckon all feasts, fasts, and holidays. The New Year that begins on the first day of Tishrei, the seventh month, is associated with the creation of the world.

After the Babylonian captivity we find the Babylonian names of the months, which are now employed in every Jewish calendar, as follows: Nisan, lyar, Sivan, Tammuz, Av, Elul, Tishrei, Cheshvan, Kislev, Tevet, Shevat, Adar and Adar Sheni, second Adar. The accepted Jewish calendar, based on the system published by Hillel II in 359 CE, makes the months to alternate between thirty and twenty-nine days. Nisan, Sivan, Av, Tishrei, Kislev and Shevat have thirty days; the other six months have twenty-nine days. In a leap year, consisting of thirteen months instead of twelve, when Adar Sheni is added, the first Adar has thirty days, the second twenty-nine. When the preceding month has thirty days, its last day is celebrated as the first day of Rosh Chodesh, while the second day of Rosh Chodesh marks the first day of the new month. Otherwise, Rosh Chodesh consists of one day.

The month can contain only whole days, and lunation requires 29 days, twelve hours, 44 minutes, 2.8 seconds, elapsing between two successive new moons; hence the alternation between thirty and twenty-nine days. This does not fully absorb the forty-four minutes 2.8 seconds above the twelve hours. For this reason, Cheshvan is as often as necessary lengthened to thirty days. Since Yom Kippur may not come on a Friday or a Sunday, on account of Shabbat, the first day of Rosh Hashanah cannot occur on Sunday, Wednesday, or Friday. Nor can Hoshana Rabbah, when the willow branches are struck against the ground at the end of the synagogue service, fall on a Shabbat. The adjustment is made at the end of Cheshvan and Kislev in the preceding year.

THE YEAR— The Hebrew name for year is SHANAH. Twelve lunar months comprise an ordinary or common year, which consists of approximately 354 1/2 days. To harmonize the lunar with the solar calendar, a nineteen-year cycle is used, during which leap years occur seven times, in the 3rd, 6th, 8th, 11th, 14th, 17th, and 19th years. The leap month is inserted in the calendar immediately after the month of Adar and is called ADAR SHENI - THE SECOND ADAR. The year in which ADAR SHENI occurs is called SHANATH ABOR - LEAP YEAR. To determine the status of any Jewish year, whether it be a leap year or not, divide the present Jewish year by 19. The answer will indicate whether or not it belongs to the serial of cycle years. Example: the year is 5763 (2002/2003), when divided by 19, the result is 303 with remainder 6. This means that we have completed 303 cycles of 19 years since the creation of the world; that we are now beginning our 304th cycle; that we are in the 6th year of that cycle and that this is a leap year. The Sabbatical Year, or Week of Years - The Sabbatical Year is ordained in the Bible (Leviticus 25:1-7). It is also known as SHANATH HA-SH’MITAH - THE YEAR OF RELEASE, or as a Shabbat rest for Hashem. During the Sabbatical Year it was ordained that the soil was not to be plowed, and the land permitted to lie fallow. Because this "release" took place every seven years it was called The Week of Years - SHANATH HASHEVAH.