Since well before the dawn of mankind, before the first wizards began bending the forces of nature to their will, a lone, silent figure has been ever watching us as we have progressed through space and time. It is the Moon, our only natural satellite, and the closest heavenly body to ours in the solar system. We are not completely sure how it got there, but we definitely should be happy it is because without it, there is a good chance life might never have come into being.

The Moon is nothing if not mysterious. We have spent hundreds of years observing it, worshipping it, and eventually even visiting it, and yet there are still things about the Moon that boggle all the leading minds, Muggle and wizard alike. Try as we might, there may always be phenomena that go unexplained, but at least we may continue to ponder these, and speculate about them. In this chapter, we will discuss some of the more inconclusive areas of lunar studies, within both the Muggle and wizarding fields.

11 a. How Was the Moon Formed?

Sitting between 350 and 400 thousand kilometers from Earth, at around a quarter the diametre of our planet, the Moon is the fifth largest natural satellite in the solar system, and the second largest relative to the size of the terrestrial body it orbits, second only to Charon, the Moon of the dwarf planet, Pluto. Whilst large, the Moon has only about 1/81 the mass of Earth. It has an abnormally small iron core, taking up only 20% of its total volume, as opposed to the average 50%. Many people suggest this is due to the most popular theory of the Moon’s formation. Around 4.5 billion years ago, a large protoplanet, roughly the size of Mars, slammed into the newly formed Earth. This caused a huge amount of debris from both planets to be ripped away into an orbit around the freshly terraformed Earth. The debris slowly coalesced into the rocky body we know today as the Moon. Because iron is much heavier than the surrounding rock in the mantle and crust, it is thought that most of the iron from the impacting planet remained on Earth after the impact, resulting in the low amount of iron in the Moon today.

11 b. Tides

Two of the most prominent effects the Moon has on us are tides and eclipses. Just as the Moon’s orbital period of a little less than twenty-eight days results from the Earth’s gravitational hold on it, the Earth is affected by the Moon’s gravity, as well. The Moon’s gravitational pull creates two bulges of water on opposite sides of the Earth, causing ocean tides twice a day. The Sun has about half the effect the Moon does on tides. When the gravitational forces of the Sun and the Moon are perpendicular to one another, especially weak tides, called Neap Tides, occur. This happens during the Quarter Moon. (See Moon Phases, below.) Spring Tides, on the other hand, are especially strong tides, occurring when the Moon, Earth, and Sun are all in a line. Spring Tides occur during the Full Moon and the New Moon. Approximately every one-and-a-half years, the very high Proxigean Spring Tide occurs, either during the New Moon phase, when the Moon is between the Sun and the Earth, or when the Moon is very close to the Earth (at its proxigee, thus explaining the name of this tide).

These same tidal forces are why we only see one face of the Moon. Long ago, the Moon spun faster than it does now, but it has since become tidally locked, and now the Moon revolves once around the planet at the same speed it rotates once on its axis. Given enough time, it is believed that the Moon eventually will stop rotating altogether, as the friction from the tidal forces slowly reduces its angular momentum over billions of years.

11 c. Moon Phases

During its rotation, part of the Moon sometimes is still lit by the Sun even after the Moon has set. Depending on which ‘phase’ the Moon is in, more or less light is reflected from the surface of the Moon back to the unlit side of the Earth. To go through one complete Moon phase takes approximately twenty-nine days. This is called the Moon’s synodic period, and comprises one lunar month or lunation. There are four key Moon phases: New Moon, when the Moon is between the Earth and the Sun; Full Moon, when the Earth is between the Moon and the Sun (similar to the New Moon, but with the Moon on the other side of the Earth); and the First Quarter and Third Quarter Moons (often called ‘Half Moons’), when the Moon is at a 90-degree angle to the Earth-Sun alignment, with half of the Moon in shadow and half in the light. Then there are four ‘in between’ lunar phases: Crescent (when less than half of the Moon is illuminated), Gibbous (when more than half of the Moon is illuminated), Waxing (when light on the Moon’s face is growing), and Waning (when light on the Moon’s face is decreasing). These ‘in between’ phases combine to create the phase names, as discussed below.

The lunar month begins with the New Moon phase, in which the side of the Moon that we see is not lit by the Sun. During the New phase, the Moon is between the Earth and the Sun, with the entire illuminated portion being on the back side of the Moon. As the Moon gradually moves toward the First Quarter phase, and more and more light can be seen on the face of the Moon, it is in the Waxing Crescent phase. Next is the First Quarter phase, when half of the Moon is illuminated. As the Moon continues on toward the Full Moon, it is more than half illuminated, but still not full, so it is in the Waxing Gibbous phase. When a Full Moon occurs, the face of the Moon is at maximum illumination. After the Full Moon, the light on the Moon’s face begins to decrease. Between the Full Moon and the Third Quarter Moon is the Waning Gibbous phase, and after the Third Quarter Moon (when the other half of the Moon is illuminated, as compared to the First Quarter Moon) is the Waning Crescent phase. Then we return to the New Moon, when the side of the Moon facing us is dark.

11 d. Eclipses

Sometimes the shadow of the Earth or Moon may get in the way of moonlight or sunlight, and this causes an eclipse. A lunar eclipse happens during a Full Moon, when the Moon passes through the shadow of the Earth causing the Moon to darken, sometimes even completely. Often, the Moon becomes an eerie, blood red Moon – beautiful, terrifying, and awe inspiring.

Conversely, a solar eclipse occurs during a New Moon. During a solar eclipse, the Moon gets between the Earth and Sun in a straight line, causing some sunlight to be blocked out by the Moon. How the Moon looks during a solar eclipse is due to some improbable serendipity: the Moon happens to take up almost exactly the same space in the sky as the Sun does, relative to their distances. In other words, because the Moon is so close and the Sun so far away, the two bodies appear to be the same size. In a solar eclipse, the Sun’s corona becomes visible as a vast white halo extending out in all directions around the dark face of the Moon.

Tides, eclipses, and the phases of the Moon are some of the most important properties of the Moon, and are the most revered in folklore, and in Muggle and wizard tales. But one of the Moon’s most ignored features could be the most important, as far as life on Earth is concerned. The Moon is pockmarked with thousands upon thousands of craters. This signifies that at some point, it endured thousands and thousands of impacts, some of which span a large portion of its surface area. The Moon has been a shield for the Earth since the early formation of the solar system, and may have caught hundreds of potential life-destroying asteroids in its 4-billion-year life. So the next time you look up at a Full Moon (after keeping an eye out for werewolves, of course), thank your lucky stars it is there, continuing to protect us from celestial harm!

11 e. The Moon Illusion

One of the most famous of the lunar mysteries comes from Muggle science. The ‘Moon Illusion’ is an optical illusion in which the Moon appears much larger at the horizon than it does when it is higher up in the sky. The reason this is an ‘illusion’ is that the Moon actually registers on the human retina as about 1.5% smaller near the horizon than when it is higher up in the sky. This type of illusion is not limited to the Moon; the same effect occurs with the Sun, and with any other extended object in the sky, such as the star constellations. The illusion has perplexed scientists and psychologists alike for centuries. Many theories have been offered in an attempt to explain this phenomenon, but no single theory has succeeded in explaining the illusion. All we know is that it happens; the ‘why’ seems to escape us.

11 f. Popular Illusion Hypotheses

There are, literally, dozens of proposed explanations for the Moon Illusion, some more plausible than others. A few of the more popular hypotheses are described here, although we will not go into great detail in this textbook, leaving more detailed study of what causes the Moon Illusion for advanced NEWT-level studies.

11 g. Angular Size and Physical Size

The ‘size’ of an object can be measures in different ways. There is an object’s physical size, which is simply the size of an object when measured with some system of measurement, such as metres. Then there is the object’s angular size, which measures how large the object appears to be to an observer (some call it the ‘visual angle’). Angular size depends on both the object’s actual size and its distance away. This is familiar to you already: things look smaller as they get farther away from you. So if you know an object’s actual size, and also how large the object looks to you, you can use a mathematical equation to calculate the object’s distance from you. Astronomers use angular size to determine how far away objects are from Earth.

One of the popular hypotheses about the Moon Illusion involves the Moon’s angular size. This hypothesis suggests the Moon Illusion begins as an angular size illusion with different possible outcomes. The Moon has a relatively constant angular size of approximately .5 degrees as it moves across the sky. However, as discussed above, for most people the Moon looks larger at the horizon than it does at its zenith. It is as if the size of the Moon changes when it is seen at various distances.

11 h. Apparent Distance Hypothesis

When we look at objects in the sky, such as birds, clouds, or a quaffle, those near to the horizon typically are further away from us than things seen overhead. (As a retired Keeper, the author can attest to this firsthand.) This perception makes it appear that as something moves from overhead toward the horizon, the object looks smaller because it is moving farther away from us. However, that is not the case with the Moon. Because the Moon is so far away from us, we do not perceive differences in its angular size. Instead, we judge its apparent distance by referring to visual cues. For instance, when we see the Moon at the horizon, we also may see cars, buildings, and the like that cause the Moon to appear further away – and larger - than when we see the Moon high in the sky, with relatively few visual cues as to its distance, causing it to look smaller. This theory evaporates, however, using a well-established observational tool: if you bend over and view the horizon Moon upside down, it will look smaller.

Researchers continue to try to explain the Moon Illusion. The ultimate explanation may end up being a combination of earlier hypotheses, involving angular size, linear size, distance, and size relative to other objects within the visual field.

11 i. Lunar Transient Phenomenon

A Lunar Transient Phenomenon, or LTP, is a short-lived change in the light (brightness), Colour, or physical appearance of the lunar surface. Claims of short-lived lunar phenomena have been documented for at least 1,000 years. Historical reports include sightings of possible volcanic eruptions on the Moon, episodes of strange luminescence or Colour changes, and swirling light changes suspected of being gaseous clouds. One catalog of historical LTP events cites over 2,000 events dating back to the 6th century. Since November 2005, Muggle and wizard astronomers in NASA’s Meteoroid Environment Group have video-taped 82 specific transient phenomena on the night side of the Moon. Twenty of these flashes of light have been identified as meteors striking the Moon’s surface. Others have been simply coincidental, such as an Earth satellite or a piece of space debris that just happened to be in the visual field during the video-taping.

Winifred S. Cameron, of the National Space Science Data Centre in Greenbelt, Maryland, USA, has classified reports of LTPs into five major categories: (1) gaseous, which involve mists and other forms of obscuration; (2) reddish colouration; (3) green, blue, or violet colouration; (4) darkenings; and (5) brightenings.

On June 18, 1178, a group of monks traveling near Canterbury reported a catastrophic event on the lunar surface just after sunset. Their account is recorded, in Latin, in the Chronicle of Gervase of Canterbury. An English translation is offered here for the benefit of those students who are not sufficiently proficient in Latin to do their own translation:

‘This year on the Sunday before the Feast of Saint John the Baptist, after sunset when the Moon was first seen, a marvellous sign was seen by five or more men sitting facing it. Now, there was a clear New Moon, as was usually at that phase, its horns extended to the east; and behold suddenly the upper horn was divided in two. Out of the middle of its division a burning torch sprang, throwing out a long way, flames, coals and sparks. As well, the Moon’s body which was lower, twisted as though anxious, and in the words of those who told me and had seen it with their own eyes, the Moon palpitated like a pummelled snake. After this it returned to its proper state. This vicissitude repeated itself a dozen times or more, namely that the fire took on tormented forms variously at random, and afterwards returned to its prior state. Even after these vicissitudes, from horn to horn, that means along its length, it became semi-black. This to me who writes this was told by those men who with their own eyes saw it, and who are willing to swear on oath that they have not added to nor falsified the above written.’

This is but one of the many detailed reports of the past thousand years or so describing major shifts in the appearance of the lunar surface. There are many theories as to how these LTPs may occur.

11 j. Outgassing

Whilst the Moon has been quiet geologically for a long time, that does not mean it is utterly silent. Due to tidal forces (see The Moon-Part I), sometimes there are ’moonquakes’ that may cause small pockets of gas trapped below the surface of the Moon to escape. Observations of these events tend to occur at the edges of the lunar maria, or seas, which are large, basalt plains formed by ancient lunar volcanic eruptions. These smooth, dark areas, covering about 17% of the Moon’s surface area, are likely locations for the formation of gas pockets.

11 k. Impact Events

Impacts are always happening on the Moon. As stated in the previous chapter, the Moon is our shield, protecting us from countless bombardments. Whilst the number of impacts is only a fraction of what it used to be, the Moon is still hit frequently by space rocks. Most of these are only micrometeorites, which are tiny, but their flashes can be detected from Earth-based observations. A large enough meteor shower could explain many historic LTPs.

11 l. Electrostatic Phenomena

It has been suggested that some LTPs may be caused by the reflection of sunlight off of rising plumes of electrostatically-lofted dust from the Moon's surface. These electrostatic discharges could be caused by friction, solar wind, or the electrodynamic charging of gases released by the fracturing of near-surface materials. Large enough discharges from these events could give rise to phenomena visible from Earth.

11 m. The Moon and Religion

The Moon has been linked to many major deities spanning all forms of polytheistic religion. One of the most well-known is Artemis, the Greek Goddess of the Hunt and the Amazonian Moon Goddess. It makes sense for Artemis to be associated with the Moon, or the Full Moon to be more precise, as hunters could see much better in full moonlight. The Moon Goddess was known as Luna by the Romans, and Selene by the Greeks. Some other notable deities sharing the Moon as their symbol are Sin, the Mesopotamian God of the Moon, and Chandra, the Hindu lunar deity, considered to be a Graha, or ‘cosmic influencer,’ on the living beings of Earth.

11 n. The Transverse Photothaumic Hypothesis

Magic is one of the most intriguing and elusive forces in the universe. We know through Magical Theory that it is, indeed, a force that has substance, and shows a remarkable plasticity. Thoughts, emotions, large concentrations of living things, and strong outbursts of energy can alter magic in one way or another. It is also thought that magic can be warped and altered by the mass of large objects, which seem to act as thaumic (i.e., magical) generators, amassing and releasing magical energy like the Sun releases solar winds. Stars, in particular, produce photons that carry some of this thaumic energy. But it is not just raw magic that causes changes here on Earth. It is speculated that over thousands of years, the beliefs we have developed about heavenly bodies have infused the energies they release with certain qualities. Although the Sun is known as a bringer of life, countless civilizations also have considered the Sun to be a vengeful deity, full of wrath and fire. When millions of people all believe that something is a certain way, their collective belief acts upon the object, like a global consciousness, rendering a certain magical resonance with the body. In essence, this explains why vampires are harmed by sunlight, and other creatures of the night run and hide at the first light of dawn.

It has been observed that light from the Moon also has some photothaumic properties. The interesting thing about these is they have almost the opposite properties of sunlight. Where many magical beasts seem to fear, or can be physically harmed by, sunlight, it seems the opposite is true in the case of moonlight. Some think this is why the baleful transfiguration brought on by the infectious bite of a werewolf can occur only when the subject is in direct contact with full moonlight. Similarly, certain potions and spells seem to be infused with greater power if wrought in moonlight. Light from a Full Moon (see The Moon-Part I) is at its highest photothaumic potency. The exact basis for the change in thaumic quality is not understood fully, but it has been postulated that moonlight can be thought of as anti-sunlight. It is also thought that the Earth, itself, may cause the change. Night has very powerful and primal connotations spanning as far back as the beginning of mankind. The night is dark, and long has been considered to be full of terrors. So it may be possible that the night side of Earth somehow is charged with this negative thaumic energy, and as the sunlight passes through the Earth’s atmosphere, the light’s pure form is tainted, rendering it a hollow shade of its original brilliance.