For as long as mankind has been watching the sky, one object more than most has stood out in the glittering heavens. The Moon is the Earth’s only large, natural satellite. It was born around the same time as the Earth when a Mars-sized object (we now call Theia) collided with our embryonic planet ejecting millions of tonnes of material into our orbit. Over a few thousand years, gravity worked its magic, pulling together the debris and sculpting it into a massive sphere of rock that has been orbiting us for four and half billion years.
Its history and movement is complicated, but people have watched its rise and fall, and morphing of phases for millennia, using it to help with navigation, time keeping and more recently, as a way of decoding the history of our solar system.
Did you know that the words ‘month’, ‘Monday’ and ‘menstruation’ all come from the word Moon (in Latin, the word for month is ‘Mensis’? It was the Romans who gave us the 12 month calendar system, as a way to reconcile the year’s periods with the number of full moons witnessed in a year.
However, due to its complicated orbit, there are sometimes 13 full moons…it is this phenomenon that has given rise to the now common phrase, ‘once in blue moon’.
In the modern world, this event refers to the second full moon witnessed in a calendar month, and, as the name suggests, this only happens very rarely – only once every 2 to 3 years. It takes the Moon twenty nine and a half days to complete this cycle, in what is known as its synodic period, and thus for us to witness it twice, the first event must occur very early on in any given month.
The first full moon last month was on the 2nd August, but on the 31st of August, the moon completed its cycle again, gracing the world with the second full moon of the month.
This interpretation is a bit of a misnomer however, and the original definition of a ‘blue moon’ stems from the farming community. The year used to be divided into four seasons of three months, based on the Sun’s movement as it passed from summer solstice to spring equinox, to winter solstice and to the autumnal equinox. When four full moons were witnessed in an astronomical season, the third was labelled a ‘blue moon’.
It was only in 1946, thanks to a poorly worded article in Sky and Telescope magazine, that the more modern definition was adopted. Interestingly, in a month with either no new moons, or two new moons, it is known as a ‘dark moon’.
Monthly Blue Moons | Seasonal Blue Moons |
May 31st 2026 | Aug 19th 2024 |
Dec 31st 2028 | May 20th 2027 |
Jan 30th 2029 | Aug 24th 2029 |
This table shows the occurrence of the next three ‘blue moons’.
It is worth noting that, for either definition, the Moon never manifests as the colour blue, much to the disappointment of many excited onlookers. There have been a few occasions where the Moon has appeared blue to naked eye observations, but these are all due to atmospheric conditions. Volcanic eruptions and massive forest fires have been known to affect the wavelengths of light penetrating the atmosphere and cast an eerie blue hue upon its face, but the Moon itself never manifests with a natural azure glow.
As another interesting, side-note, half of the Moon’s surface is always lit by the Sun. The only difference is the angle that we view it from here on Earth, and thus how much of the lit area we can see. When the Moon is full, the Sun is on the opposite side of the Earth, thus illuminating the Moon’s full face from our perspective. As the Moon orbits Earth, its angle changes and we see less and less of the lit half, until the Moon is between us and the Sun (New Moon). When this happens, the far side of the Moon is still up by the Sun, but we are not privy to this light until it passes the Sun and we see the lit area growing until full once again. This is what gives rise to the lunar phases we know so well. As the amount of light lessens, the Moon is said to be waning, and when its is returning to full, it is waxing.
Full Moons have often been associated with behaviour, in both animals and people. The phenomenon has been around for almost as long as the Earth and it is thus not surprising that life has adapted to its changing light. There are countless examples in nature of organisms reacting to lunar phases. Dung beetles navigate by the light of the Moon, taking a bearing from its light to guide their ball-rolling antics. Birds use the position of the Moon to aid in navigation. The joint pine, or Mormon’s tea (Ephedra foeminea) is a tree species found in the Mediterranean region that uses the light of the Moon to aid in its reproduction. It is a gymnosperm, meaning that it produces no flowers, but is reliant on nocturnal moths and flies to pollinate itself. During full Moon, it produces a sweet, sticky fluid that glows in the moonlight to attract its suiters.
Perhaps the most famous example of organisms using the lunar cycle is found in corals. These amazing creatures only spawn once a year, just after a full Moon, when the water temperature is just right. They do this because the full Moon causes strong tides, aiding their reproductive cells to be spread far and wide by the ocean’s currents.
It is worth noting again here however, that while the Moon causes our tides, its phase does not play any role in tidal strength. In fact, its tidal pull on our oceans is the same regardless of its phase. The Moon’s mass (and influence on our water) does not change at all as it moves around the Earth, but at full Moon, the Sun, Earth and Moon are all lined up in single direction (known as ‘syzygy’), and the combined influence of both the Sun and the Moon pulling on the same plane accentuate the affect. This is known as a ‘spring tide’ and the addition of the Sun’s gravity causes tidal variance to be much greater.
Due to the human body being made up of 70% water, popular culture has long assumed that the full Moon (with the additional gravitational influence of the Sun) can have an effect on our behaviour. The word ‘lunatic’ is derived from this idea. But many experiments have been done on this topic and no official correlation has been found. This is unsurprising considering that scientists have shown that the change in gravity and pressure felt in our bodies at full Moon, is around a million times less than the pressure of resting one’s head on a pillow at night!
Despite scientific evidence to the contrary, stories of erratic behaviour abound so be on the look-out for werewolves just in case!!
