BLSChronology

Article I.4 Biblical New Year: The Full Moon After the Vernal Equinox Method

 

"Observe the month of Abib, and keep the passover unto the Lord thy God: for in the month Abib the Lord thy God brought thee forth out of Egypt by night."  — Deuteronomy 16:1

"Let the children of Israel also keep the Passover at its appointed season."  — Numbers 9:2

When God established the biblical calendar, He didn't leave the timing of His appointed feasts to guesswork. The method for determining the start of the biblical year—and therefore the correct timing for Passover—was designed with both seasonal accuracy and astronomical precision. The system that emerges from Scripture and ancient practice is elegantly simple: The biblical year begins with the new moon whose 14th day (full moon) falls on or after the vernal equinox.

Why This Method Makes Sense

The Seasonal Requirement

The Bible clearly establishes that Passover must occur in the proper season. The month name Abib means "green ears of grain," indicating the spring barley harvest. This seasonal anchor prevents the lunar calendar from drifting into winter or summer—Passover must remain a spring festival.

The Lunar Framework

Scripture consistently uses lunar terminology:

  • Chodesh (month) literally means "new moon"
  • Major festivals occur on specific numbered days of the month
  • The 14th day consistently represents the full moon phase

 

The Divine Appointment

Numbers 9:2 emphasizes that Passover has an "appointed season" (Hebrew: moed)—a divinely scheduled time, not a human approximation. This suggests God built precision into the calendar system itself.

Understanding the Vernal Equinox

The vernal equinox (from Latin ver = spring, aequinoctium = equal night) is one of the most important astronomical events for calendar purposes. But what exactly is it?

The Astronomical Reality

The vernal equinox occurs when:

  • Day and night are nearly equal in length (approximately 12 hours each)
  • The sun crosses the celestial equator moving northward
  • The sun rises due east and sets due west everywhere on Earth
  • The sun's declination equals zero (directly above Earth's equator)

 

Why It Happens

Earth's axis is tilted 23.5 degrees relative to its orbital plane around the sun. This tilt creates our seasons:

  • Winter: Northern hemisphere tilted away from sun (shorter days)
  • Summer: Northern hemisphere tilted toward sun (longer days)
  • Equinoxes: Earth's axis perpendicular to sun-Earth line (equal days/nights)

The vernal equinox marks the moment when Earth transitions from winter to summer positioning—the astronomical beginning of spring in the northern hemisphere.

Ancient Observations

For ancient peoples without modern instruments, the equinox was observable through:

  1. Equal shadow lengths at sunrise and sunset
  2. Sun rising precisely due east and sets precisely west
  3. Day and night feeling equally long
  4. Seasonal temperature shifts beginning

 

Biblical Significance

According to Psalm 74:16-17: "The day is thine, the night also is thine: thou hast prepared the light and the sun. Thou hast set all the borders of the earth: thou hast made summer and winter."

The "borders of the earth" in direct context with "summer and winter" refers to the equinoxes—the astronomical boundaries that divide the seasons. These borders are determined by "the great heavenly light (the sun)" in accordance with Genesis 1:14.

The vernal equinox marks the astronomical beginning of spring—when day and night are equal length and the sun crosses the celestial equator moving northward.

Ancient peoples could determine this moment with remarkable accuracy using a simple sundial method:

 

How the System Works

Step 1: Determine the Vernal Equinox

The vernal equinox marks the astronomical beginning of spring—when day and night are equal length and the sun crosses the celestial equator moving northward.

Ancient peoples could determine this moment with remarkable accuracy using a simple sundial method:


The Shadow Technique:

 

[Diagram: Sundial shadow method for equinox determination]

  • Place a vertical stick in the ground before sunrise
  • At sunrise, mark the morning shadow on the ground
  • At sunset the same day, mark the evening shadow
  • Use a straight reed to measure the angles between the two shadows
  • When the shadows form a perfect straight line = vernal equinox
  • The smaller the angle, the closer to equinox
  • When angles appear on opposite sides, equinox has passed

This method required no special instruments and was accurate to within a day or two—sufficient precision for calendar purposes.

 

Step 2: Decide the New Year by Shadow Angle and Crescent Moon

The size of the shadow angle showed how near the equinox was. When the small crescent moon appeared (1–2 days after the new moon), observers judged whether the upcoming full moon (≈14 days later) would fall on or after the vernal equinox.

  • If yes → the new year began that very night with the new crescent.
  • If no → the new year was still declared, but it meant the full moon would fall slightly before the equinox, leaving the year off by only a day or two.

 

Step 3: Confirm by the Full Moon

The full moon acted as a confirmation:

  • If it fell on or after the equinox → the decision was perfectly aligned.
  • If it fell just before the equinox → the new year had already started and could not be undone; the celebrations stood, though the reckoning was off by a day or two.

This approach shows how the system balanced astronomical precision with practical observance—anchoring the biblical year to spring without needing modern instruments.

 

Why Other Methods Fall Short

The Barley Growth Method

While agricultural readiness is important, relying solely on crop inspection creates problems:

  • Regional variations in growing conditions
  • Weather-dependent rather than astronomically reliable
  • Subjective judgment about when grain is "ready"
  • No way to predict the date in advance for planning

 

The New Moon After Equinox Method

Some propose the year should begin with the first new moon after the equinox, but this creates difficulties:

  • The 14th day might fall too late in the season
  • Less precise seasonal alignment
  • Doesn't account for the full moon requirement in Scripture

 

Biblical Evidence Supporting the Full Moon Method

"This month shall be your beginning of months: it shall be the first month of the year to you... In the tenth day of this month, they shall take to them every man a lamb... And ye shall keep it up until the fourteenth day of the same month: and the whole assembly of the congregation of Israel shall kill it in the evening." Exodus 12:2-6

This passage establishes:

  • A specific month as the beginning of the year
  • Precise day counting within that month
  • The 14th day as the culmination (Passover)

"In the fourteenth day of the first month at even is the Lord's Passover." Leviticus 23:5

The 14th day is consistently specified, indicating the full moon was the target date.

"Blow up the trumpet in the new moon, in the time appointed, on our solemn feast day." Psalm 81:3

This connects the new moon (beginning of month) with the appointed time of the feast—suggesting a systematic relationship between lunar phases and sacred timing.