Full Moon

A full moon occurs when the Moon reaches the halfway point of its orbit—that is, when it is directly opposite the Sun, with Earth in between.[1] The phenomenon of a Full Moon arises when our planet, Earth, is precisely sandwiched between the Sun and the Moon. This alignment ensures the entire side of the Moon that faces us gleams under sunlight.[2] The definition of the full moon is the phase of the lunar cycle where the entire lunar disk, or the half of the moon we see, is illuminated.[4]

Astronomical Mechanics

A cycle starting from one Full Moon to its next counterpart, termed the synodic month or lunar month, lasts about 29.5 days.[2] The eight lunar phases are, in order: new Moon, waxing crescent, first quarter, waxing gibbous, full Moon, waning gibbous, third quarter, and waning crescent. The cycle repeats about once a month (every 29.5 days).[5]

Due to its position opposite the Sun, the full moon rises at sunset and sets at sunrise.[1] Full Moon occurs when the Sun and Moon are at nearly opposite positions in the sky - which is why a Full Moon rises about the time of sunset, and sets about the time of sunrise, for most places on Earth.[9]

Though a Full Moon only occurs during the exact moment when Earth, Moon, and Sun form a perfect alignment, to our eyes, the Moon seems Full for around three days.[2] At New Moon the percent illuminated is 0; at First and Last Quarters it is 50%; and at Full Moon it is 100%.[9]

Orbital Variations

When the Moon reaches the point in orbit closest to Earth (perigee), it can appear from Earth as much as 14 percent larger in the sky than at its farthest point (apogee).[1] When a full moon occurs close to the perigee, it is often regarded as a supermoon, a term coined in the 1970s. This phenomenon usually occurs in about four or five consecutive lunar cycles per year.[1]

When a Full Moon is close to the perigee, it looks slightly larger in the sky and is known as a Supermoon or Super Full Moon. When a Full Moon is close to the apogee, it appears a bit smaller and is called a Micromoon.[3]

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.[3] A Blue Moon is the second Full Moon in a month that experiences two Full Moons. This phenomenon graces our skies roughly every 2.7 years.[2]

Lunar Eclipses

The geometrical relationship between the Moon, Earth, and the Sun can cause other night-sky phenomena, such as lunar eclipses, which occur only during the full moon when the Moon travels into Earth's shadow, or umbra, and thus appears darker (and sometimes tinted red) in the sky.[1]

But two to four times each year, a full Moon occurs when the Moon's orbit intersects Earth's plane of orbit, placing the Moon in Earth's shadow — and a lunar eclipse occurs![6] The Moon's orbit around Earth is tilted a little, or "off kilter" by about 5 degrees to the Earth's orbit around the Sun. This means that most of the time the Moon is slightly above or below Earth's plane of orbit — and out of the shadow cast by Earth where it blocks the Sun's light. No eclipse occurs during these full Moons.[6]

Tidal Effects

The Moon's gravitational tug causes Earth's waters to bulge, birthing tides. During both Full and New Moons, the Sun, Earth, and Moon are in alignment, generating "spring tides." These tides can swing exceptionally high or low due to the combined gravitational influences of the Sun and Moon.[2]

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.[3]

Traditional Names and Cultural Significance

Many cultures and civilizations across history have used the moon cycles to keep track of passing time, and some gave names to the full moons that often referenced the climate or agriculture of a given "month."[1] Ancient cultures gave the Full Moons names like Flower Moon and Harvest Moon to track the months and seasons. These names are still in use today.[21]

Although the most commonly used Full Moon names are English interpretations of Native American names, some are also Celtic, Anglo-Saxon, medieval English, and Neo-Pagan. Many of the names come from the Colonial Americans adopting Native American names into their calendars, according to the Old Farmer's Almanac.[21]

Each full Moon marks the completion of a month, a concept known as "moon time." Cultures across North America ascribed names to each full Moon throughout the year based on significant seasonal activities that took place during its Moon time.[22] In reality, most Native American tribes have their own set of full Moon names, and those names reflect each tribe's customs and regional climate and ecology. Nevertheless, some common themes are easy to spot: winter weather, crop availability, and fishing and hunting cues find expression in Moon names.[25]

Monthly Names

The January Full Moon is often called the Wolf Moon from the howling of hungry wolves in the winter. This name is thought to have a Celtic and Old English origin, and that European settlers brought it to North America.[21] Typically a time of heavy snowfall in North America, February is when winter gives one final flourish. With the ground blanketed in white, it's easy to understand why the full Moon name known by many tribes is the Snow Moon.[22]

This name is traditionally thought to refer to the earthworms that appear as the soil warms in spring. Alternatively, during his travels in the 1760s, Captain Jonathan Carver wrote that this Moon name refers to a different sort of "worm"—larvae—which emerge from the bark of trees and other winter hideouts.[24]

Technically, the Harvest Moon is the Full Moon closest to the September equinox around September 22. The Harvest Moon is the only Full Moon name determined by the equinox rather than a month. Most years, it's in September, but around every three years, it falls in October.[21]

Global Traditions

In Japan, the name tsukumi literally means "looking at the Moon" but is commonly used to name the tradition of viewing the Harvest Moon. Koreans call it chuseok, and it is similar to the Mid-Autumn Festival in China.[21] In Sri Lanka, the Full Moon is called Poya and each Moon has its own name and a dedicated holiday. Listed here in the order January-December: Duruthu Poya, Navam Poya, Madin Poya, Bak Poya, Vesak Poya, Poson Poya, Esala Poya, Nikini Poya, Binara Poya, Vap Poya, Ill Poya, and Unduvap Poya.[21]

Religious and Mythological Significance

As the largest and brightest object regularly seen in the sky besides the Sun, the full moon has persisted as a symbol in legend, religion, and even agriculture across many cultures. For example, in Hinduism, full moon days, or Purnima, are often celebrated by fasting. Full moon days have historically been significant to followers of Buddhism, and full moon rituals are common in Neo-Paganism and similar movements.[1]

In Europe the full moon was believed to trigger uncontrollable behaviour in what was known as the "lunar lunacy effect," which inspired tales of werewolves and other beasts that broke free only under the full moon's light. Today the full moon is still associated with erratic behaviour and an increase in crime rates, though these ideas are an urban legend.[1]

The Lunar Society of Birmingham

The Lunar Society was an informal group of prominent Midlands industrialists, natural philosophers, and intellectuals who met regularly in Birmingham, England during the Age of Enlightenment in the late 18th century.[14] It met in and around Birmingham, England between 1765 and 1813.[13]

The Lunar Society derived its name from the fact that its members would meet on the Monday closest to the full moon, which provided natural illumination for their journeys home.[14] Their meetings took place at the time of the full moon, this enabled the members to proceed home by its light.[18]

The group included prominent figures such as James Watt, Erasmus Darwin, Joseph Priestley, and Matthew Boulton, who were at the forefront of the Industrial Revolution in Britain.[14] The Lunar Society was a group of free thinking scientists and industrialists including Joseph Priestley, Erasmus Darwin, Josiah Wedgwood, James Watt, and William Withering.[18]

The Lunar Society played a crucial role in the development and diffusion of new technologies, including the steam engine, the chemical industry, and advancements in agriculture and transportation.[14] The meetings held here were lively affairs, where all the latest ideas and inventions were discussed and scientific experiments carried out.[18]

The Lunar Society was neither the first nor, in the long run, the most scientifically significant of the provincial societies to be organized in eighteenth century Britain; of the towns possessing them, Birmingham might reasonably be thought one of the least likely to have produced a society worthy of particular notice. Yet, since the middle years of the nineteenth century, when its story began to be reconstructed, none of the provincial societies has attracted the attention of historians as has the Lunar Society.[17]