Calendars: The Lunar Calendar – The Moon and the Mo’edim

A visual representation of the gradual lunar phases visible from Earth, as the Moon orbits the Earth over a course of 29.5 days. The Sun (in the background) gives light to the Moon. Image credit: Unknown

Shalom, everyone! The ancient pre-exilic Israelites used two calendar systems to keep time: A civil solar calendar for day-to-day civil business and an ecclesiastical lunar calendar to track the monthly and annual mo’edim and the reigns of kings.  In Exodus 12:1-2YAH commanded the Israelites to create the ecclesiastical lunar calendar for the mo’edim, even before their Exodus from Egypt. This calendar was to be separate from but complement the civil solar calendar they had lived under since the time of AbrahamYAH also commanded that this ecclesiastical lunar calendar begin in the Spring, and opposed their civil solar calendar which always began in the Fall. The ecclesiastical lunar calendar was used by the priest to determine the dates for the mo’edim when all Yisrael were to stop their creative work (melachah), gather and have a holy convocation before YAH. The only mo’ed that is not subject to the ecclesiastical lunar calendar is the weekly Shabbat, which was tracked with the civil solar calendar.

The Moon

The Moon is the celestial object that orbits the Earth and is the Earth‘s only permanent natural satellite. The Moon is the second-brightest visible celestial object after the Sun in the Earth‘s sky. YAH created the Moon as the lesser light to rule the night, however, the Moon does not shine its own light; it merely reflects the light of the Sun in a diminished form so that the Earth can experience nighttime. The Moon is in synchronous rotation with the Earth, that is, it will always show the same side to the Earth. This side is called the near side of the Moon. The far side of the Moon, the side that is never seen from the Earth, is also called the dark side of the Moon.

The Moon‘ has an elliptical (uneven) orbit around the Earth. Its orbital distance is approximately 384,402 kilometers/238,856 miles away from the Earth. The point when the Moon‘s orbit is closest to the Earth each month is called its perigee when the Moon is approximately 363,776 kilometers / 226,040 miles away. The point when the Moon‘s orbit is furthest from the Earth each month is called its apogee when the Moon is approximately 404,457 kilometers / 251,318 miles away. The Moon‘s apogee occurs approximately 14 days after its perigee each month. The point when the Moon comes nearest to the Sun is called its perihelion, which occurs annually approximately 14 days after the arrival of the Summer Solstice when daylight is longest. The point when the Moon is furthest from the Sun is called its aphelion, which occurs annually approximately 14 days after the arrival of the Winter Solstice when daylight is shortest. The Moon has a gravitational influence on the Earth‘s crust and ocean tides. The shape of the directly-lit portion of the Moon‘s surface as viewed from the Earth is called the lunar phase or the phase of the Moon.

The Lunar Phases

As mentioned previously, the shape of the directly-lit portion of the Moon‘s surface as viewed from the Earth is called the lunar phase. The lunar phase changes gradually and cyclically over a period of approximately 29.5 days, as the Moon orbits around the Earth, and the Earth orbits around the Sun. The Moon makes a complete orbit around the Earth in relation to the fixed stars about every 27.3 days (sidereal period) however; because the Earth itself is rotating and has its own orbit around the Sun, it takes longer for the Moon to show the same lunar phase to the Earth, visually extending its monthly orbit to 29.5 days (synodic period). There are usually 12 lunar months each year. The lunar calendar year has about 354 days, about 11+ days shorter than the solar calendar year of 365.2425 days. For this reason, if operating solely off a lunar calendar, the dates for the mo’edim will be out-of-sync and move across the seasons. It is, therefore, necessary to also consult the civil solar calendar to accurately determine the dates for the annual mo’edim. The two calendars were meant to complement each other and to be used concurrently.

The following is a list of the lunar phases (phases of the moon) occurring during each lunar month. The lunar phases are presented below in the order in which they would have appeared at the time of Creation and afterward. Each lunar month is about 29.5 days. The images presented are the view of the Moon from the Earth‘s Northern Hemisphere. The view from the Southern Hemisphere would be 180-degrees opposite (upside down). These images are from various sources via Wikipedia:

# Lunar Phase Visibility from Earth Average Moonrise Average Moonset Illumination
(Northern Hemisphere)
(Southern Hemisphere)
View from Northern Hemisphere
1 Full Moon Sunset to sunrise (all night) 6 pm 6 am Completely illuminated disc  Completely illuminated disc
2 Waning Gibbous Moon Most of night and early morning 9 pm 9 am Left side, 99–51% lit disc Right side, 99–51% lit disc
3 Third (Last) Quarter Moon Late night and morning Midnight Midday Left side, 50% lit disc Right side, 50% lit disc
4 Waning Crescent Moon Pre-dawn to early afternoon 3 am 3 pm Left side, 49–1% lit disc Right side, 49–1% lit disc
5 Dark Moon None 6 am 6 pm  Disc completely in Sun’s shadow Disc completely in Sun’s shadow  None
6 Waxing Crescent Moon Late morning to post-dusk 9 am 9 pm Right side, 1–49% lit disc Left side, 1–49% lit disc
7 First Quarter Moon Afternoon and early evening Midday Midnight Right side, 50% lit disc Left side, 50% lit disc
8 Waxing Gibbous Moon Late afternoon and most of night. 3 pm 3 am Right side, 51–99% lit disc Left side, 51–99% lit disc

The Lunar Months and Mo’edim

The ecclesiastical lunar calendar utilizes the lunar phases to track time during a lunar month. Each full moon marks the beginning of a new month, each month being about 29.5 days, and each lunar year having 12 or 13 full moons. In ancient pre-exilic Israelite culture, it was the full moon that marked the beginning of the month, and neither the dark moon nor the first sighting of the waxing crescent moon. The first moon ever was a full moon when Elohim created this celestial object on Day 4 of Creation. The Moon was created as the lesser light to rule the night; only the full moon lives up to the role of ruling the night as during this lunar phase the moonlight shines at its brightest. The Israelites were later commanded to celebrate each new “full” moon with a monthly “new moon day” festival. The dark moon could not be the lunar phase to be celebrated as the “new moon” as it is invisible to the naked eye from Earth. Neither could the waxing crescent moon be the new moon because its light is diminished. It was not until after being exiled to Babylon that the Israelites adopted the Babylonian lunisolar calendar system of using the first sighting of the waxing crescent moon as the new moon.

On the ecclesiastical lunar calendar, only four of the lunar months had actual names. These lunar months with actual names were as follows:

  1. The First Month was named “Aviv“;
  2. The Second Month was named “Ziv“;
  3. The Seventh Month was named “Ethanim“;
  4. The Eighth Month was named “Bul.”

These lunar months were given names most likely because they have the greatest concentration of the annual mo’edim. Each lunar month has at least one mo’ed, however, it is in the named months that most of the annual mo’edim occur. The following is a list of the lunar months and their respective mo’edim:

Full Moon # Lunar Month Given Name Season Mo’edim
1  First Month  Aviv  Spring Rosh Chodesh 1(New Moon Day 1),
Pesach (Passover),
Chag HaMatzot (Feast of Unleavened Bread),
Sefirat HaOmer (Counting of the Omer)
2  Second Month  Ziv  Spring Rosh Chodesh 2 (New Moon Day 2),
Pesach Sheni (Second Passover),
Sefirat HaOmer (Counting of the Omer)
3  Third Month  None  Spring Rosh Chodesh 3 (New Moon Day 3),
Sefirat HaOmer (Counting of the Omer)
Shavuot (Feast of Weeks/First Fruits)
4  Fourth Month  None  Summer Rosh Chodesh 4 (New Moon Day 4)
5  Fifth Month  None  Summer Rosh Chodesh 5 (New Moon Day 5)
6  Sixth Month  None  Summer Rosh Chodesh 6 (New Moon Day 6)
7  Seventh Month  Ethanim  Fall Rosh Chodesh 7 (New Moon Day 7),
Yom Teruah (Day of Blasting/Shouting),
Yom HaKippurim (Day of Atonement),
Sukkoth (Feast of Booths)
8  Eighth Month  Bul  Fall Rosh Chodesh 8 (New Moon Day 8)
9  Ninth Month  None  Fall Rosh Chodesh 9 (New Moon Day 9)
 10  Tenth Month  None  Winter Rosh Chodesh 10 (New Moon Day 10)
11  Eleventh Month  None  Winter Rosh Chodesh 11 (New Moon Day 11)
12  Twelfth Month  None  Winter Rosh Chodesh 12 (New Moon Day 12)
13  Thirteenth Month  None  Winter-Spring Rosh Chodesh 13 (New Moon Day 13).

Note: A 13th full moon is only counted in years when the signs of Spring have not been fully confirmed by the end of the 12th lunar month.

Calculating the Dates for the Mo’edim

There are two turns of the year. The first turn of the year occurs in the Spring, the second turn of the year occurs in the FallSpring begins with the arrival of the Vernal (SpringEquinox on approximately March 20-21 of each year. Fall begins with the arrival of the Autumnal (Fall) Equinox on approximately September 22-23 of each year. The civil solar calendar begins with the turn of the year that occurs in the Fall. The ecclesiastical lunar calendar begins with the turn of the year that occurs in the Spring. Because the ecclesiastical lunar year begins in the Spring, the First Month usually begins with the first full moon sighted after the arrival of the Vernal Equinox. There are other factors to consider, however, before declaring a new year for mo’edim on the ecclesiastical lunar calendar. Please note that these factors are relevant in the Northern Hemisphere:

  • Arrival of the “latter” rains: These rains occur in the Spring, and are necessary for the ripening of grain (flax, barley, wheat, oats etc.) which is harvested in Spring;
  • Maturity of the grain harvest: The grain seeds are declared mature for harvest once they have reached full growth and have filled with the necessary starch;
  • Migratory patterns of the birds: Birds which flew south for the winter season will begin heading back north in the Spring;
  • Synchronization of the full moon with the turns of the year, Spring and Fall: The First Month must begin in the Spring. Counting from the first full moon after the Vernal (Spring) Equinox, the seventh full moon in the sequence must occur close to or after the arrival of the Autumnal (Fall) Equinox on approximately September 22-23. If the next full moon after the twelfth full moon arrives prior to the Vernal (Spring) Equinox, then the count of the first full moon for the new year is delayed by one lunar month until the following full moon immediately afterwards. In this scenario, a closing lunar year acquires a 13th full moon. This is done so that the mo’edim will be celebrated in their appropriate seasons, Spring and Fall. Pesach and Chag HaMatzot (Feast of Unleavened Bread) must be celebrated in the Spring. Yom Teruah, Yom HaKippurim and Sukkoth must be celebrated in the Fall. If the 13th full moon is not added to the closing lunar year, over time the seasons will move out-of-sync.
  • In order to confirm the arrival of Spring and Fall, it was necessary to consult with the civil solar calendar.

In ancient times, the priests of Israel were tasked with the responsibility of determining when the mo’edim would occur during the course of the lunar. As a result of the Assyrian, Babylonian, Persian and Roman exiles, the Levitical priesthood is no longer accessible to the majority of the Erverh community in the Diaspora. Fortunately, however, increased knowledge and technology enable us to know when the mo’edim will occur. There are a number of resources at our disposal which enables to accurately project when the mo’edim. The annual Old Farmer’s Almanac and websites such as and publish the dates of the lunar phases, the equinoxes, and solstices for the upcoming year. We also now have access to electronic calendars, for example, Google Calendar, or which enable us to use the information from previously mentioned resources to generate an accurate lunar calendar for the mo’edim. We will demonstrate how to use these technological resources to map out an accurate ecclesiastical lunar calendar in a later post. These resources, however, do not absolve our community of learning about the signs in nature of how to determine the seasons. YAH gives us signs in nature of how to determine the seasons. He wants us to learn as much as possible about nature as it, like us, is His Creation, and we dwell in and interact with nature at every moment.

We will demonstrate how to use the above-mentioned technological resources to map out an accurate ecclesiastical lunar calendar in a later post. In the meantime, if you use Google Calendar, please follow our public calendar Mo’edim and Holidays for an ecclesiastical lunar calendar synchronized to the Gregorian calendar. All times are based on the east coast USA time zone.



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