The Lunar Calendar and How Moon Phases Work

March 12, 2020

5 minutes read

Human cultures from our oldest records have used the moon phases to record time. Ancient societies across the world observed and measured the Lunar Calendar to understand its influence on their lives.

Today, the lunar calendar is used across the world including the Chinese calendar, Islamic Calendar, Native American, pre-historic English, Pagan, Celtic, and Indigenous Australians amongst many others.

Why is there a Lunar Calendar?

All calendars track the astronomy of earth relative to other bodies in the solar system. The moon is the earth’s only satellite, meaning it revolves around our planet. While the Gregorian Calendar measures the solar year (our orbit around the sun), the moon is the next important factor.

The Lunar Calendar marks how the earth, sun, and moon move in relation to each other.

A lunar month lasts 29.53 days.

That’s the period for the moon to complete its orbit around the earth in relation to the sun. (We’ll explain this next).

Today moon cycles affect the sea tides, farming, reproductive cycles, and nearly all systems on earth. It’s apparent that ancient societies had a deep knowledge of these.

What is the effect of the moon on earth?

At 1/6 the size of earth, the moon’s gravity is a powerful influence on the planet. It causes the rise and fall in sea levels known as tides. Tides even occur in lakes, the atmosphere, and within Earth’s crust. High tides are when water bulges upward, and low tides are when water drops down.

Here are some quick facts on the moon. They explain the moon’s influence on planet earth.

Moon’s Distance From Earth:	225,745 miles
Length of a Moon Day:	27.3 days
Moon’s Radius:	1,080 miles
Moon’s Diameter:	2,160 miles
Moon’s Weight:	81 Quintillion Tons
Moon’s Surface Temp (Day):	273° F
Moon’s Surface Temp (Night):	– 244° F
Moon’s Gravity At Surface:	0.1667 g (1/6 Earth’s)
Moon’s Orbital Speed	2,287 mph

Why do we see moon phases?

Earth, Moon and sun relationship determines the moon phases as seen from earth. Source

The Lunar Calendar is broken up into 8 moon phases.

Each moon phase shows how the moon looks from earth. When we look at the moon we will see the sunlight reflecting from it.

One half of the moon is always lit up by the sun. From earth, we only see one surface of the moon all of the time. The different portion of that area illuminated defines the moon phases.

Use the picture above to understand each moon phase.

IMAGE EXERCISE: For each phase, picture yourself standing on earth. You are looking at the moon in its relation to the sun and how the sunlight affects that view. The outside circle is how the view will look.

What causes phases of the moon?

Many people think that moon phases are caused by seeing the shadow of the earth on the moon. That is not correct. Our view from earth shows the portion of the moon lit up by the sun.

The moon phases change as the angles between the earth, sun, and moon shift.

What is a lunar eclipse?

A lunar eclipse is when the moon passes through the earth’s shadow. It’s a rare event.

What are the 8 phases of the moon?

The 8 moon phases defined by sunlight in relation to the earth and the moon.

Now let’s look at the names and exact meanings of the 8 moon phases.

(1) New Moon – The moon starts as it sits between the sun and earth. Its sunlit surface faces directly away from our view. The surface of the moon we view from earth is in full darkness. In this phase, the moon and sun, rise and set at about the same time.

(2) Waxing Crescent Moon – As the moon orbits the sun begins to light the surface facing earth. It is called the waxing moon phase. It starts with a sliver of light in view shaped like a crescent. During the waxing period, the crescent gradually grows.

(3) First Quarter Moon – One week after the new moon, the Moon has completed a quarter of its orbit around the Earth. At this stage, we can view half of the surface lit by sunlight. Its shape is a perfect half circle, called the first quarter moon phase.

(4) Waxing Gibbous Moon – Over the next week, the sunlit surface of the Moon grows. The period after the first quarter moon is called waxing gibbous. Gibbous means “humped”.

(5) Full Moon – Two weeks after the new moon, the moon reaches halfway of its orbit. The half that is facing the earth is now fully lit by the sun’s light. From earth, it appears as a round disk or full moon. Like the new moon phase, it rises at the time the sun sets. The full moon also sets when the sun rises.

When the moon aligns exactly with the Earth and sun, it is a lunar eclipse. However, its orbit is 5 degrees off so doesn’t happen very often. At this angle sunlight normally flows past the earth to reflect off the moon’s surface.

(6) Waning Gibbous Moon – In the waning moon periods, the sunlit moon surface we can see decreases. The first week after the full moon, it is called waning gibbous.

(7) Last Quarter Moon – Three weeks after the new moon, half of the illuminated part of the moon can be seen. This is usually called last quarter moon or third quarter moon.

(8) Waning Crescent Moon – By the fourth week of the cycle, the Moon is reduced to a thin sliver. It’s sometimes called the waning crescent moon

After the waning crescent phase finishes the new moon begins again.

Now we’ve covered the entire moon cycle.

How many days are between each moon phase?

A lunar month can be defined as the time the moon takes to pass through each of its phases. Starting at new moon to first quarter moon, full moon then the third quarter moon, and returns back to its starting position. A lunar month takes 29.53 days, although this varies slightly, and the number is an average.

As a new moon occurs every 29.53 days. It is called a synodic month. All lunar calendars are based on these months rather than the months you find on a solar calendar.

The moon orbits the Earth at the same time it takes to rotate once. As a result, the moon always shows the same face to the Earth.

That’s why you never see its far side or the dark side of the moon. (We’ll explain that more in other articles).

Is the Lunar Calendar more accurate?

The lunar month lasts 29.53 days. So twelve lunar months accounts to about 354 days. This is short of the 365 days that it takes the Earth to orbit the Sun. So after about 3 years, the lunar months are out of sync with the solar year by about a month. Some calendar systems account for this and it takes 33 years to line back up again.

The solar Gregorian Calendar that we use today has problems. Leap years are used to account for inaccuracies. But it still drifts one day roughly 3216 years.

Lunar calendars can have an error of only about 2 seconds per year. That equates to 1 day in 31,250. On this measure, it is roughly ten times more accurate than today’s Gregorian calendar.