The Jubilees Calendar was a solar calendar which included feasts and annual Sabbaths (holydays) which differed from the lunisolar calendar of traditional Jews (Bowker, 1969, p. 27). It consisted of a solar year of 364 days divided into seven-day weeks, and twelve months of thirty days each, except for one extra day in the last month of each quarter.

The Essene sect observed the weekly Sabbath as did other Jews, but unlike the Pharisees and Sadducees, they adhered to the Jubilees Calendar also known as the Qumran Calendar. D. David Flusser (1917-2000), an Israeli professor of Early Christianity and Judaism of the Second Temple Period at Hebrew University of Jerusalem, suggested that the Essene calendar differed significantly from that of the priests in order for the Essenes to distance themselves from the Jerusalem establishment (Flusser, 1995, p. 43).

According to this calendar, the major feasts, e.g., the Feast of Unleavened Bread, the Feast of Trumpets, the Feast of Tabernacles and the Last Great Day (the day after the seven day Feast of Tabernacles) always began on Wednesday. These days commenced the evening the day before as the Jews began days at evening not midnight (Simon 1967:73). Trumpets, Tabernacles and the Last Great Day always occurred in the seventh month of their calendar.

The first day on the first month (Month I) always began at sunset (Jerusalem time) on the Tuesday evening following the vernal equinox (Finegan 1998:46). That is, annually, the Essenes set or fixed their calendar such that day 1 of the first month 1 was the fourth day of the week (Jewish Wednesday or Tue./Wed.). They did not begin their new year on the day of the vernal equinox unless the equinox occurred on the third day of the week (Jewish Tuesday or Mon./Tue).

The Essenes, who followed this solar calendar, always observed the Passover on a Tuesday night. The Essenes fixed Nisan 14 on their calendar as the third day of the week, sunset Monday night to sunset Tuesday night or simply Tuesday as we reckon time. The Passover Sabbath, the annual Sabbath known as the first day of the Feast of Unleavened Bread, then always began at sunset Tuesday night and ended at sunset Wednesday night. This means of marking time differs from our Gregorian calendar wherein specific weekdays are not preset to exact dates.