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How Does a Moon Phase Calculator Work?

If you’re a worshipper of the moon—as so many of us are—it’s important to understand at any given time what phase the moon is currently in. How do you do that? A moon phase calculator allows us the convenience of looking up the moon phase of any date: past, present, or future!

Today, we’re delving into the history of lunar calendars and exactly how moon phase calculators work as well as why it can be tricky to calculate moon phases on your own.

The History of Lunar Calendars

Lunar calendars have been around for centuries, dating back to about 380 BC. In fact, throughout history, our ancient ancestors measured time by the number of moons that passed during a specific time period and by the shadows that both the sun and moon cast.

The Sumerians were the first to begin using a lunar-based calendar, whereas the Greeks shortly after adapted it and then the Romans did the same. These cultures and civilizations created calendars based around the phases of the moons, also known as “lunations”, and the seasons that surrounded those phases. Since it was possible for individuals to identify different moon phases with the naked eye, it became an effective way to measure time, and thus, the lunar calendar was born.

How Does a Moon Phase Calculator Work?

Fast forward to present day, and although perhaps in different ways than it did historically, the lunar calendar still has relevance in today’s world. To aid in our understanding of when the different lunations have previously and will in the future occur, the convenience of moon phase calculators is at our fingertips, especially thanks to technology.

moon phase calculator

Because of the way the moon orbits our planet, the portion of this orb that we see illuminated changes in cycles over time. Taking advantage of an online moon phase calculator allows us to easily decipher when the moon is in which phase. A full trip around the earth takes the moon 29.5 days, a full cycle measured from one new moon to the next. These handy calculators quickly determine which calendar day each phase takes or has taken place over each day of a given month or subset of time. Some moon calculators also highlight special and rare moon events, such as harvest and blue moons.

How Long Do Moon Phases Last?

There are eight total lunations in the moon’s 29.5 day cycle: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter and waning crescent. However, deciphering how long each lunation is is not as simple as dividing the entirety of the cycle by eight, which is what makes an electronic moon phase calculator so valuable.

While that 29.5 day cycle, otherwise referred to as a “synodic month”, is an exact and reliable number time after time, the actual length of each moon phase can’t be boiled down to a specific number that remains true cycle after cycle.This is because the motion of the moon, calculated by its orbital speed and position, can be affected by a number of forces.

For this exact reason, trained experts use complex equations to take these varying factors into account to create each year’s moon phase calendars and calculators. Some of these changing factors are what provide us with notable lunar events, such as eclipses and rare moons.

moon phase calculator

As you can see, moon phase calculators make it simpler than ever to determine what moon phase hung in the sky on the evening of any special event and what phases you can expect on specific days to come. The steady yet fluid nature of the moon makes it as wondrous and inspiring as it is to us all, and it’s certainly interesting to follow and continue learning about in our day-to-day lives!


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