The Hebrew calendar (luah) is a systematic arrangement of the days of the year, reckonng the days from evening to evening, in keeping with the biblical order of Creation. The present Jewish calendar is lunisolar, the months being reckoned according to the moon and the years according to the sun. A month is the period of time between one conjunction of the moon with the sun and the next. The conjunction of the moon with the sun is the point in time at which the moon is directly between the earth and the sun (but not on the same plane) and is thus invisible. An important element in the current Jewish calendar is the announcement of the exact occurrence of Shabbat, festivals, and fasts, all noted here. The solar year is 365 days, 48 minutes, and 46 seconds, which means that a solar year exceeds a lunar one (12 months) by about 11 days. The cycles of 12 lunar months must therefore be adjusted to the solar year, because although the Jewish festivals are fixed according to dates in months.
הסכמות: ר' מרדכי בנעט, ניקאלשבורג, ח טבת תקפ"ה; ר' אליהו אהרן לאטאש, ויניציאה, ד שבט תקפ"ו; ר' אברהם ריגייו, גוריציאה, ראש-חודש מרחשון תקפ"ו; ר' אברהם אליעזר הלוי, טריאסטי, כח אלול תקפ"ד.