The
Hebrew calendar is a lunar calendar based on 19-year cycles. The
following sections explain the principles of this calendar.
The
Torah (Old Testament) inscribes to follow the lunar
calendar, which contains exactly 29 days, 12 hours,
44 min, 3 1/3 seconds.
July 21, 1969, a retro reflector array left on the
Moon by Apollo 14 astronauts. A 2-foot wide panel
studded with 100 mirrors pointing at Earth. Lunar
laser ranging works by firing pulses of laser light
at reflectors on the Moon's surface and catching
the returning photons. |
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A laser pulse shoots out of a telescope on Earth,
crosses the Earth-moon divide, and hits the array.
Because the mirrors are "corner-cube reflectors,"
they send the pulse straight back where it came
from.
It able them to track exactly a full mouth cycle.
The results came to be exactly 29 days, 12 hours,
44 min, 3 1/3 seconds. God most likely know what
he was talking about.
Units of Time
Thecalculations
in the subsequent sections are based on an ancient
form of measuring time. Each day is divided into
24 hours, which are each divided into 1080 parts
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A
month is defined as the period from one new moon to the
next, corresponding to the astronomical definition of a
siderial month. For these calculations the length of a month
is taken to be exactly 29 days, 12 hours, 44 min, 3 1/3
seconds .
The
Biblical date of creation is used as the basis for the Hebrew
calendar. Reverse calculation gives the time of the first
new moon of Year 1 as 5 hours and 204 parts from the beginning
of the second day of the week (Monday). This date corresponds
to October 7, 3761 BCE, using the Julian (not Gregorian) calendar.
For later arithmetic convenience, we will define the preceding
Sabbath as day number 0, so that this date, 1 Tishrei
of Year 1, is day number 2.
Types
of Years
A year in theHebrew
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 intercalated in seven of every nineteen years
(years 3, 6, 8, 11, 14, 17, and 19). Every 19-year cycle thus
contains 235 months. These two cycles of years and months
are so close that they diverge at the rate of only 4.5 days
every 1000 years. Because
a lunar month is not a whole number of days (29 days....)
the length of the months can be either 29 or 30 days to
equal out. A typical year alternates 30- and 29-day months,
beginning with Tishrei, which is 30 days. In leap
years, Adar I is 30 days and Adar II is 29 days. To further
bring the calendar into alignment with the lunar cycle,
a year may need to be shortened or lengthened by one day:
Kislev may be shortened to 29 days, or Cheshvan
may be lengthened to 30 days. Thus, there are six types
of years:
- Defective common years, with 353 days
- Regular common years, with 354 days
- Excessive common years, with 355 days
- Defective leap years, with 383 days
- Regular leap years, with 384 days
- Excessive leap years, with 385 days
An
ordinary year has 353, 354, or 355 days. The three lengths
of the years are termed, "deficient," "regular,"
and "complete," respectively.
An
ordinary year has 12 months, every month starts on the day
of a new moon.
The months and their lengths are:
| Name |
Number |
Length |
Gregorian
Equivalent |
| Nissan |
1 |
30
days |
March-April |
| Iyar |
2 |
29
days |
April-May |
| Sivan |
3 |
30
days |
May-June |
| Tammuz |
4 |
29
days |
June-July |
| Av |
5 |
30
days |
July-August |
| Elul |
6 |
29
days |
August-September |
| Tishri |
7 |
30
days |
September-October |
| Cheshvan |
8 |
29
or 30 days |
October-November |
| Kislev |
9 |
30
or 29 days |
November-December |
| Tevet |
10 |
29
days |
December-January |
| Shevat |
11 |
30
days |
January-February |
| Adar |
12 |
29
or 30 days |
February-March |
| Adar
II |
13 |
29
days |
March-April |
The
month Adar I is only present in leap years. In
non-leap years Adar II is simply called "Adar."
Note that in a regular year the numbers
30 and 29 alternate; a complete year is created
by adding a day to Heshvan, whereas a deficient
year is created by removing a day from Kislev.
The alteration of 30 and 29 ensures that when
the year starts with a new moon, so does each
month. |
A year is a leap year if the number year mod 19 is one of
the following: 0, 3, 6, 8, 11, 14, or 17.
The
years are counted since the creation of the world, which
has taken place in 3761 B.C.E. In that year, AM 1 started
(AM = Anno Mundi = year of the world). In the year C.E.
2000 we have witnessed the start of Jewish year AM 5760.
The Jewish day does not begin at midnight, it begins at sunset
(or when three medium-sized stars should be visible, depending
on the religious circumstance). Sunset marks the start of
the 12 night hours, whereas sunrise marks the start of the
12-day hours. This means that night hours may be longer or
shorter than day hours, depending on the season.
The first day of the Jewish calendar year is Rosh Hashanah,
the first of Tishri. It starts on the day of the new moon
that occurs about 354. (Leap year would have different status)
Besides Rosh Hashanah being the Jewish New Year, there are
some other new years within Judaism. Such as the 15 of Shevat:
well known as Tu B'shevat. - The New Year for trees, when
fruit tithes should be brought.
The first of Nisan: is the New Year for Kings. Nisan is considered
the first month, although it occurs 6 or 7 months after the
start of the calendar year. And at last the first of Elul:
New Year for Animal Tithes (Taxes). |
