How Many Full Moons in a Year?
Most years have 12 Full Moons, one each month. However, our calendar is not perfectly synchronized with astronomical events. Therefore, now and then, a year has 13 Full Moons. When this happens, at least one of those Full Moons is called a Blue Moon.
Lunar Libration: The Rocking Moon
The Moon orbits Earth counterclockwise on an elliptical path when looking down at the Earth’s North Pole, and the same side of the Moon always faces Earth. During a Full Moon, this near side is fully illuminated, allowing us to see half of the Moon’s surface.
But did you know that, over time, we can actually see 59% of the lunar surface—even though only 50% is visible at any one moment? This is because the Moon rocks slightly from north to south and wobbles a little from east to west in what astronomers call lunar libration.
Higher Tides at Full Moon
The most significant difference between high and low tide is around Full Moon and New Moon. During these Moon phases, the Moon’s and the Sun’s gravitational forces combine to pull the ocean’s water in the same direction. These tides are known as spring tides or king tides.
Third Primary Moon Phase
Full Moon is the third of the four primary phases of the Moon, which occur at specific moments in time. The other three are New Moon, First Quarter Moon, and Third Quarter Moon.
In addition, there are four intermediate lunar phases that take up the time in between the primary phases. These are Waxing Crescent Moon, Waxing Gibbous Moon, Waning Gibbous Moon, and Waning Crescent Moon.
It takes around 29.5 days to move through the eight Moon phases.
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Cultural and Religious Significance
The Moon—especially the Full Moon phase—has influenced human culture for millennia. The date for Easter Sunday, for example, is determined based on approximations of the dates of the vernal equinox and the Full Moon following it. And, even today, people use ancient Full Moon names, like the Harvest Moon and the Strawberry Moon.
The Moon has also inspired the invention of countless deities, like the Roman goddess Luna or her Norse male counterpart Máni, who gave his name to Monday.
In the past, it was common to think that the Moon caused mental illness, hence the name lunatic. The Full Moon has even been held responsible for supernatural transformations, changing otherwise harmless men into ferocious werewolves.
Sleep, crime, and menstruation: how Full Moons affect humans