ASTR-201 Lessons

2.2: Phases and Tides

In this lesson we will discuss two aspects of the Moon: phases and tides.  To start with the basics, tides are caused by the gravity of the Moon and the Sun, and phases are caused by the Moon’s revolution around Earth.   But that doesn’t mean that lunar magic will not be discussed in this lesson!  The Moon’s phases affect many of our magical practices, and tides strengthen some of the spells we cast - in particular water charms.  Since water is one of the four elements, this sort of magic is called elemental magic, which is the subject of the last part of today’s lesson.  But first, bear with me while I tell you about the phases and tides themselves, which you’ll need to know about in order to be able to take full advantage of them in your magical activities.

Phases of the Moon

We have already briefly discussed that the Moon goes through different phases, but we have not listed them all. The lunar cycle starts with the new Moon, which is when the Moon is not visible to us on Earth. Gradually, as the cycle continues, a sliver of Moon starts to appear, bringing us to the waxing crescent phase (waxing, in this case, means growing). Then, when half the Moon is visible, it reaches the next phase, called the “first quarter.” It is named as such because it marks the beginning fourth of the lunar cycle. Moving on, the Moon then goes through the waxing gibbous phase, when more than half of it, but not all of it, is lit, until it finally becomes a full Moon. This occurs on the 15th day of the cycle, after which the Moon’s visible area starts to shrink, passing through the waning gibbous (waning here means shrinking), third quarter, and waning crescent phases before finally reaching the new Moon again, ending the lunar cycle.

Diagram of the Moon's phases. Earth is at the centre of the diagram and the Moon is shown orbiting Earth (dashed circle). The Sun lights half of the Moon and Earth from the right side. The phase of the Moon is shown next to the corresponding position of the Moon in its orbit around Earth. 

Source: here  

The picture above shows the various phases and respective positions of the Moon with respect to Earth and the Sun.  Note that, in the image, the Moon revolves counterclockwise around Earth, so that the phases occur in the order described above.  Note that when the Moon is waxing, its right side is lit, and when it is waning, its left side is lit.  That is true from anywhere far enough north of the equator, including Hogwarts. Just to make it difficult to remember, however, these sides are reversed if a person views the Moon from the Southern hemisphere.

A lunar cycle lasts about 30 days, but as we learned last year, it takes the Moon less than 28 days to revolve around Earth.  Why is this?  Well, while the Moon is completing its revolution, Earth is also revolving around the Sun, so the Moon must go a little further than one full revolution in order to catch up with the Sun in the sky!

I mentioned in the last lesson that 59% of the Moon is visible from Earth instead of only half of it.  Interestingly enough, this has a magical significance!  The far side of the Moon looks different from the near side: more craters and less contrast between light and dark areas.  This means that the far side reflects less magic to Earth, so when a sliver of it is facing us, we get a wee bit less magic.  For all we know, the magic reflected by the far side is different from that reflected by the near side.  Unfortunately, the one spacecraft that has landed on the far side of the moon (the Chinese rover), wasn’t equipped to test for that sort of thing. 

Yes?  You want to know why we can see more than half the Moon?  Well, the Moon’s orbit is inclined about five degrees to that of Earth, allowing us to see a sliver of the north and south sides of the Moon as it goes about its revolution.  In addition, the Moon rotates at a constant speed, but it moves faster in its orbit when it’s at perigee and slower at apogee, allowing us to also see a sliver of the east and west sides.  A video which shows how this works can be found here. You can see how an extra bit of the top, bottom, left, and right sides of the Moon are visible at different points in the lunar cycle. 

The best time for viewing the Moon is during its first quarter or its third quarter, since the angle of the Sun causes the mountains to cast long shadows on the plains, resulting in greater contrast between light and dark than during the other phases.  However, the best time for viewing other celestial objects in the night sky is during a new Moon or, at most, a crescent Moon, as otherwise the moonlight is too bright and washes them out.  Then by process of elimination, the worst time to do any viewing of the night sky is during a full Moon, unless you’re using a Muggle-built telescope (and there are no werewolves anywhere in your vicinity)! However, as we will see in Lessons Four and Six, a full Moon does have its advantages. 

If all of this is starting to sound a little complex to you, as mentioned in your First Year, a lunascope or a moon chart can be used to show the phase of the Moon on any given date, which will help you decide on which nights to sacrifice some sleep depending upon what you want to do.  

Phases and Magic

Now, after all that, some of you may be asking the age-old question “why do I care?” The answer to this question is not a simple one; there are many reasons. Those around you who have grown up in magical families or are particularly observant will have noticed that the phases of the Moon govern many different aspects and subjects of magic -- from alchemy to transfiguration -- though some areas are more obvious than others. Potions, as a start, is one of the most intertwined subjects with astronomy. Not only do the phases of the Moon impact when some ingredients should be harvested, but the lunar cycle also plays a role in how long potions need to brew, when to start or stop brewing a potion, and even when to add specific ingredients. Speaking of ingredients, this naturally affects herbology as well. Each phase of the Moon has subtle differences that influence a plant’s usefulness or applications. For example, plants harvested under a full Moon tend to have much stronger effects, whereas plants harvested under a new Moon are better for those with allergies or sensitivities (though, as I’m sure your Herbology professor would encourage you, please always seek guidance from a healer before consuming any plant, particularly one you are allergic to).

Alchemy is likewise related, particularly in the area of transmutations. The Moon, Sun, and planets all play an important part in the timing of successfully transmuting metals. Additionally, many ancient alchemical elixirs also have the same moon-based considerations as regular potions.

Magical creatures are also thralls to the Moon and its phases. The poor lycanthrope is the most popular example, as they transform against their will when the Moon is full. However, this is not the only lunar factor affecting creatures. Ramora, highly endangered, most often surface during a new Moon, whereas Clabberts come out into the open to mate during a full Moon, when the light disguises their glowing forehead pustules from predators. Additionally, Augureys only build their nests during a waning Moon, for reasons that magizoologists haven’t entirely been able to pinpoint.

Don’t go thinking that it’s all about animals, vegetables, and minerals, though. Even your average spell is influenced by the Moon (and other celestial bodies, but one thing at a time). Lunar magic tends to strengthen your spell casting power, and the more of the Moon that is lit in the sky, the greater this effect is.  But not every spell ought to be cast during a full Moon.  For some spells, there is an optimal amount of lunar magic that makes them at once safe and effective.  The more the lunar magic exceeds this optimum, the more chance there is for the spell to backfire.  The more it falls short, the more chance there is for the spell not to work at all.  The optimal phase is different for different spells, as you’ll find out during your study of charms, defence against the dark arts, and transfiguration.

We can’t cover every single area of importance in one lesson, but I hope these fundamentals give you the right idea. Further specifics, other than these little tidbits, will be addressed as needed in their individual classes – this is just to whet your appetite. And, should you have questions about the phases of the Moon in any particular circumstance, feel free to come to me with questions. That said, here are a few general rules and associations to round off this section.

New Moon

During this phase, the Moon reflects no magic to Earth, so it doesn’t strengthen any spells, but it does have some other benefits.  For example, as mentioned earlier, many nocturnal magical creatures are more active around the new Moon, as they are least likely to be noticed then, since they are under the cover of darkness (much like the Ramora).  A surprisingly large number of spells and potions have been discovered during the new Moon, when compared to the rest of the phases, suggesting that in the absence of any input from lunar magic, we are encouraged to experiment with new ideas.

Half Moon

This lunar phase is a bit of an odd child, with few strengths, but also relatively few weaknesses. Theoretically, it is a great time for novices or students to practise new spells, as backfires are quite unlikely (due to magic being neither stronger than expected, nor weaker, which requires you to slightly overpower your spells).

Full Moon

As long as the Moon isn’t being eclipsed and the Sun is far enough below the horizon that it doesn’t interfere destructively with lunar magic, spells related to water are strongest during this lunar phase, whether as complex as summoning a torrential downpour or as simple as filling a glass. Additionally, magical power in general is slightly more available during the full Moon, as more of the Sun’s magic is being reflected towards Earth. 

Waxing Moon

The waxing Moon, whether a gibbous or a crescent, is associated with an enhanced connection to one’s Inner Eye (if you put stock in that sort of thing). It is also generally associated with improvement, such as becoming stronger or more intelligent. Thus, potions or spells meant to have these effects will be both easier and more potent under this phase. 

Waning Moon

Saying the waning Moon is associated with weakness certainly gives it a negative connotation, but that isn’t necessarily accurate. It also has some desirable effects, such as boosting the immune system in fighting magical illnesses. Additionally, spells intended to weaken an opponent, such as sleeping spells or stunning spells, are easier to cast. 

Having shown you the magical significance of the Moon’s phases, I’ll now turn to ocean tides, but don’t worry - I’ll be discussing their magical effects as well.

Tides

Has anyone here ever seen tides in action? I imagine many of you who are from coastal areas or who have visited the ocean have seen them. Along the shores of some bodies of water, you can easily see that the water rises and falls twice per day. If you stay in the same location for a month (and spend a significant amount of time on the shore), you may notice that the tidal range – the difference between the water level at high tide and at low tide – changes throughout that period of 30 days. On some days, there might not be much difference, but on others, the water level may be very high and then soon become very low. The latter is called a spring tide, whereas the former is a neap tide.  There are a few ways to remember this, but the one I always used was that the spring is very rainy, and therefore very wet, so spring tides are very high. That said, the tidal range also depends on your location.  In the open ocean, the tidal range is about 0.6 metres (two feet), but it is more pronounced close to the shore, especially in narrow bays, which act as funnels, amplifying the tide.  The biggest tidal range on Earth is 16.3 metres (53.5 feet) in the Bay of Fundy, in Canada.

What causes these fluctuations, you might wonder. Well, tides are caused by two things: the gravity of the Sun and that of the Moon (hence its coverage in this lesson).  We will use the images below to better picture how this works, but before we jump into it, to briefly clarify, no there are not two Moons. There are just two positions of the Moon that cause the same condition or effect. Additionally, the points marked “LW” and “HW” mean “low water” and “high water,” respectively, and correspond with high and low tides.

The first thing you might notice in this illustration is that the Moon’s gravity appears to make the water bulge on both sides of Earth.  How this works is a bit too complicated to explain in this lesson, but if you’d like to take a deeper dive, there’s a helpful article about it here.  Nevertheless, it is because of these dual bulges that we have two high tides and two low tides every day - as Earth rotates, a particular location will pass both the bulge nearer and opposite the Moon throughout the 24 hour period.

Spring and Neap Tides

Source: here

Another thing you can see from this diagram is that spring and neap tides occur at certain times related to lunar phases. The top image shows a spring tide, which happens during both the full and new Moon.  A spring tide has the most extreme difference in water levels because the Sun and the Moon pull on Earth along the same line (during a phenomenon called a “syzygy” - when three astronomical bodies are in a line). The bottom image shows a neap tide. During a neap tide, the Moon and the Sun pull on the oceans with perpendicular gravitational forces (forces that are 90 degrees from each other), essentially cancelling each other out. Neap tides occur during the first and third quarter, when we have a “half moon.”

Due to the timing of the Moon’s cycle and Earth’s rotation, the timing of the tides depend on your location.  You can use a tidal timetable to help you predict the high and low tides on each day. These charts can also predict the dates and times of spring and neap tides.

What’s that?  You’re wondering about what the phrase “tidally locked” has to do with tidal forces?  Well, the Moon used to rotate a lot faster than it revolved, but Earth’s tidal forces on the Moon caused friction that slowed down its rotation until it coincided with its revolution around Earth.  A more detailed explanation can be found here for those of you itching for more specifics.  Interestingly enough, this friction also heated up the Moon.  While not very impactful for our moon, this same phenomenon was responsible for melting ice beneath the surfaces of Jupiter’s moons, Europa and Euceladus, and led to volcanoes on Io, increasing the magic coming from that satellite of Jupiter.

Going back to our diagram, you may wonder why the water bulges towards and away from the Moon rather than the Sun during neap tide even though the Sun’s gravitational pull on Earth is much stronger than that of the Moon.  Well, the Sun’s tidal force is weaker than the Moon’s for reasons that are too complicated to be explained now, but, for those of you who are mathematically inclined, I’m going to give you two numbers, and I promise that something interesting will come of them.  The Sun pulls Earth 176 times as strongly as the Moon does, but the Sun’s tidal force is only 0.44 times as strong as the Moon’s.  Now divide 176 by 0.44 and tell me whether the answer you get seems familiar to you.  Did you all hear that?  Mr. Laxer said the answer is 400, and that’s how much farther the Sun is than the Moon from Earth.  Well done!  No, that’s not a coincidence.  It’s a general rule, which I’ll explain to you in Seventh Year.  Okay, the rest of you can start paying attention again, because we’re moving on to some magic.

Elemental Lunar Magic

And now for the part of the lesson that you’ve all been waiting for: a discussion of this type of lunar magic.  The Moon has a particular connection to elemental magic: it has a strong effect on water charms cast by a witch or wizard.  One such important charm is the Water-Making Spell, whose incantation is Aguamenti.  It conjures a jet of clean, drinkable water from the caster’s wand, making it unique to other conjuration spells, as the water doesn’t vanish after a period of time.  Further details about this spell, including its other spellcasting components and applications, will be taught in Year Six of both Charms and Transfiguration.  Suffice it to say here that strengthening this spell to make it conjure more water and shoot it farther from the caster would certainly be useful for putting out a fire that you don’t want to get too close to.  Other water charms that lunar magic strengthens include, but are not limited to, the Liquid-Parting Charm, the Fountain Charm, and the Whirlpool Charm, all of which are discussed in Year Four of Charms.

The strength of elemental lunar magic’s effect depends on certain conditions.  It can pass through clouds and through walls of buildings, but not through the whole Earth, so for it to have any effect, the Moon must be above the horizon.  The greater the Moon’s A.M.E., the stronger its effects on elemental magic will be, so most water-based magic will be at its strongest during a full Moon when the Sun is sufficiently far below the horizon.  It’s also stronger the nearer you are to the ocean, because the tidal motion spreads the magic hitting the water to nearby places, and the faster the motion is, the more of the magic it spreads. Consequently, water magic is also heightened during a spring tide, which, as you recall, happens when the Moon is full!  Do you remember that I promised to tell you the magical significance of there being two high tides and two low tides every day?  Recall from the diagram we looked at earlier that high tide takes place around noon and midnight, and low tide around six A.M. and six P.M during a spring tide.  The fastest motion of the water occurs midway between high tide and low tide, and that happens four times a day - at roughly three A.M., nine A.M., three P.M., and nine P.M. - so if you’re near the ocean, you have four chances per day instead of only two if you would like to cast more powerful water charms.

If you want to have some fun with this, on the evening of a full Moon, go to a place on the shore of the ocean where the tides are the most extreme, specifically when the water is rising or falling the fastest, and cast the Water-Making Spell. For an added bonus, use your absolute maximum willpower and see how far you can make the water shoot from your wand. Having tried this myself in my youth, I can tell you it makes for quite the competition and a good day at the beach.

Aside from being a rousing leisure activity, the effect of the Moon on elemental magic has played a large role in many discoveries. Researchers are known to experiment with new water-based spells under various phases of the Moon depending on their end goal. When working on a healing charm, for example, many will experiment under the first quarter Moon since, as you will recall from earlier in the lesson, the waxing phases lend themselves to improvement, which is the goal for healing, and the half Moon makes the spells neither too strong nor too weak. Interestingly, the only known successful casting of the Hurricane Conjuring Spell was done during the hunter’s blue moon of 1944. This interesting phenomena occurs when there is a second full Moon in the month of October, the first full Moon of the month being the harvest moon. There are other, similarly intriguing effects of the Moon on water magic, but alas, there are too many to fit into our short time here in class.

 Concluding Remarks

On that note we conclude this week’s lesson.  There will be no essay, just the usual ten-question quiz, which will cover the various topics of the tides, phases, and their effects on magic.

The original lesson was written by Professor Turing

Part of this lesson was written by Professor Plumb.