You can sense it just by looking at the thing.
It's the Moon.
Our satellite has a great effect on us. It seems to be almost a living presence in the sky. This is true no matter what phase of the Moon you look at, but is especially the case with the full Moon. Even I, as a committed rationalist, feel this.
The full Moon seems to have a special energy that affects things down here on Earth: an energy that may even have the power to affect the human brain.
This is the origin of the word lunatic (luna: Latin for moon): a person whose mind is so close to being unbalanced that the power of the full Moon is enough to tip it over into insanity.
And of course on the night of the full Moon anyone who is prone to lycanthropy should stay indoors - because they will have turned into a werewolf.
These are effects of the full Moon that supposedly affect humans (of which werewolves are a subcategory), so their veracity may be open to question on the grounds that we humans are very susceptible to suggestion. However, it seems that the full Moon can affect animals too, which are surely neutral when it comes to opinions and influences.
Let's have a look at an example.
The effect that the Moon has on animal life may be observed on certain sandy beaches of the tropics, where in the summer months during the nights around the full Moon the sands may be seen to start mysteriously shifting and churning all along the shoreline.
Just beneath the sand's surface finger-length baby turtles are hatching from the clutches of turtle eggs that had been laid and buried there by their mothers. The tiny turtles break through to the surface to be greeted by the great big face of the full Moon. Not the crescent Moon, nor the gibbous Moon - but the full Moon (Of course there'll always be premature baby turtles and overdue baby turtles, which don't get their timing right, but they are very much the exception).
What more proof do you want of the power of the full Moon? Baby turtles, still curled up in their eggs, buried beneath the sand, are unbiased when it comes to attitudes as to whether or not the full Moon has any remarkable powers - they just do what they do.
Indeed, buried in their eggs under the warm tropical sand the little turtles can't even see the Moon to know that it's full. They don't even know what the Moon is. How much did you know about astronomical bodies before you were born? The actions of the baby turtles seem to speak louder than any words of the power of the full Moon - the turtles seem to hatch because the full Moon is exerting some strange force over them.
Or could there possibly be a more mundane explanation for why they hatch at the time of the full Moon? Let's look at it more soberly.
Surely, when it comes to timing, it would be sensible for the little turtles to hatch from their eggs when conditions are at their best for their potential survival in a hostile world.
Night seems like a good time to hatch, because during the day there are a lot of nasty seagulls around looking for a snack that might be scurrying across the beach.
How do the turtles know it's night, buried as they are under the sand? Do they know it's night because they can feel the full Moon in the sky through some mysterious sense that we can only guess at, or do they simply notice that the sand's got a bit cooler now that the Sun's gone down? I'll go for the second possibility. If there's a simple, boring explanation, go for it.
But why hatch at the full Moon? Because at the time of the full Moon the tides of the sea are at their highest.
When the mother lays her eggs she lays them above the level of the highest tide (so that they don't get washed away in mid incubation). If the baby turtles hatch at the highest tide they'll have less distance to scamper to get to the sea.
How do the hatchling turtles know that the full Moon is in the sky, creating a very high tide? The "mystical" explanation may be that they have a mysterious Moon sensing organ that triggers them into action when the full Moon is overhead.
There's a more mundane explanation though.
Mother turtles lay their eggs at around the time of the high tide created by the full Moon - the mother turtles are aware of the state of the tide and can see the Moon in the sky, so there's no mystery as to how they know that there's a full Moon. The incubation period of the eggs is a month, so the eggs hatch at the next full Moon (give or take a night).
It's as simple as that.
This is a much more boring explanation that the one concerning unusual Moon-detecting powers. In fact it's such a disappointingly boring and unremarkable explanation that it seems that it may be right. The more boring an explanation is, the more likely it is to be correct.
(To fine-tune their hatching to coincide as closely as possible with the high tide of the full Moon I would suspect that the fully developed, but unhatched, baby turtles may press into use an ability to detect when the tide's at its highest by feeling the vibrations of the waves crashing quite near to them on the beach. But I'm just guessing. Again mundane, and thus worthy of consideration.) So it turns out that it's simply the tides that affect the hatching of the turtles, rather than some mysterious lunar power. What's more, it's the localised effects of the tide on the beach that are significant, not the tidal effect itself. In other words, the turtles are affected by the state of the sea, not by the state of the Moon (although its light is extremely useful).
The Moon's tidal pull may not directly influence the behaviour of turtles, but perhaps the pull can be the explanation for the Moon's supposed effect on other things.
It's often said, for instance, that because the Moon creates tides in the sea, it must surely also create "tides" in everything else too. Such as in people's brains. And perhaps in women's wombs. This would perhaps explain the supposed monthly mental imbalance of lunatics and the undisputed month-long female menstrual cycle.
This is an interesting speculation that deserves looking into. But first let's have a closer look at how the Moon affects the tides that we know about for sure - the ones in the sea.
It's generally known that the pull of the Moon on the Earth's oceans creates the tides, and that the heights of the tides vary with the phases of the Moon - with some of the highest tides occurring at the time of the full Moon.
However, as well as there being a very high tide at the full Moon there's also a very high tide at the new Moon..
A high tide at the new Moon? That's a bit strange isn't it - isn't the new Moon the time when there's no Moon? Yet it has the power to affect the waters of the world so much? No Moon - what am I talking about? Of course there's a Moon. It's simply that it's so close to the Sun that you can't see it. The Moon is obviously always in the sky: it's just that at different times its surface is illuminated differently - that's what its phases are after all.
When, for instance, the Moon appears to us as a crescent (Figure 25), what is actually happening is that the half of the Moon that is illuminated by the Sun is mostly facing away from the Earth, so all we can see is a thin edge of the illuminated half.
As the Moon proceeds in its orbit of the Earth we see different amounts of the part of it that's illuminated by the Sun, as shown in Figure 26.
(If you're thinking that you don't need this schoolbook explanation of the phases of the Moon - because it's common knowledge - my apologies for wasting your time. However, in my experience it's surprising how many people don't know the cause of the phases, regardless of their level of education. Maybe it's the sort of thing that you learn as a child or not at all.)
What you're looking at when you look at the crescent Moon very definitely isn't just an object that in its entirety is a thin curved strip suspended in the sky - despite appearances. The rest of the Moon's still there, a great big round ball of rock - unilluminated and therefore invisible.
This is all really obvious when you say it, but we don't think like that all the time. When I see the crescent Moon in the sky, in my own mind that narrow, curvy, pointy thing is all there is that exists of the Moon. The fact that there is a huge unnoticed rocky globe nestling between the horns of that crescent doesn't even cross my mind.
It takes some effort to remember that the Moon doesn't actually grow (or shrink) as its phase changes - that the whole phase thing is just an attention-grabbing lighting effect.
I'll come back to this interesting way in which we perceive the Moon later, but for now let's go back to the tides.
While it may be true that surprisingly few people are aware of the underlying cause of the phases of the Moon, I think it can safely be said that most people are aware that the tides are the result of the Moon's effects. But even so, surprisingly few are aware of the actual processes involved.
Here is a quick summary of those processes.
Before we look at the way that the Earth and the Moon (and the Sun) actually interact to create the tides, it's a good idea to imagine what the oceans of the world would be like if the Moon and the Sun weren't there to exert an influence on them. Imagine the Earth suspended alone in space, without the Moon or the Sun in attendance. Not only that, purely for simplicity's sake imagine that the Earth is a perfectly smooth sphere rather than the slightly knobbly object that it really is.
On this simplified version of the Earth the oceans would be of an equal depth all round its surface (Figure 27).
Now let's introduce the Moon, orbiting the Earth. Ignore the Sun for now.
The Moon is quite a massive body, and it's quite close to the Earth, so its gravitational pull on the Earth is far from negligible.
The pull is strong enough to pull the waters on the Earth's surface towards the Moon - which is the effect that we experience as the tides. These effects are shown in Figure 28.
The gravitational attraction of the Moon pulls the oceans of the Earth into a bulge of water on the moonward side of the Earth, as you'd expect.
But Figure 28 shows something that's at first sight quite unexpected. The water is not only bulging out on the moonward side of the Earth, it's also bulging out on the other side of the Earth too. Surely that's the wrong side? It's tempting to think that the water in this opposite bulge must be being "pushed away" from the Moon, because that's what it looks like - which all seems very counterintuitive. However, this isn't what's happening at all.
To understand what's going on you have to bear in mind that the Moon isn't only pulling the water on the Earth's surface towards itself, but is pulling the whole Earth too. The Moon is pulling on the Earth and its oceans together - it isn't simply pulling the water and dragging it round the Earth towards itself as you may have thought. What's more, the pull of the Moon gets weaker with distance, so the side of the Earth that's further from the Moon is pulled less (along with the water on that side). The result is that the whole Earth, including the water on it, is slightly "stretched" towards the Moon. A good way to visualise this is to think of an image of the Earth on a sheet of stretchy material such as rubber (Figure 29). When one edge of the sheet is held stationary and the other is pulled, the perfectly circular image on the sheet stretches into something like an ellipse. This ellipse-like form is what gives us the twin bulges of the tides.
These twin bulges are the reason why there are two high tides a day rather than just one.
The Moon isn't the only celestial body that influences the Earth's tides however. That would be just too simple.
The Sun also pulls on the oceans, in the same way as the Moon. The pull of the Sun is about half as strong as that of the Moon due to the great distance of the Sun. This creates a similar though smaller tidal effect (including its own twin bulges), which is added to that of the Moon to give the resulting tides.
Due to the fact that the Sun and Moon are usually pulling on the Earth from different directions the combined tidal effect of the pair is quite complicated and varies depending on the relative positions of the two bodies in the sky.
For instance, when the Sun and the Moon are more or less at right angles to each other relative to the Earth (Figure 30) their tidal pulls are perpendicular to each other, with the result being that the respective bulges that they create in the oceans are at right angles to each other too. The bulges therefore don't overlap, and indeed cancel each other out to some extent as they have to share the finite amount of water that's in the oceans between them. This creates relatively unspectacular tides, with lower high tides (and higher low tides) than would be caused were only one of the bodies exerting an influence. These tides are known as neap tides.
In contrast, when the Sun, the Moon and the Earth are lined up, the pulls of the Sun and the Moon combine to create very high tides indeed, known as spring tides (Not named after the season, but after leaping upwards).
Figure 31 shows the configuration of the Earth, Sun and Moon at the time of a full Moon, and the resulting spring tide.
You can see that the Sun and the Moon are pulling at the Earth from opposite sides. Although the Sun and the Moon are pulling on the Earth from totally different directions their effects don't cancel out however, due to the fact that the twin bulges that are induced by each body are added together - producing extreme tides. It's a bit like stretching the Earth from opposite directions in a cosmic tug-of-war game.
Now look at Figure 32, which shows the situation at the time of a new Moon.
Here the Sun and Moon are in the same direction in the sky (meaning that the Moon is therefore invisible to us on Earth), and their forces are pulling together, again creating extreme tides.
So it is that the tides of the new Moon are very much the same as those of the full Moon.
However, ask most people which phase of the Moon creates the most extreme tides and they will almost inevitably say the full Moon - purely because the full Moon imposes its presence on us so that we notice it. Yet, despite appearances, the reclusive new Moon is the showy full Moon's equal. The moral of this is - beware of appearances.
(You may have noticed that this moral is something of a recurring theme in this book.) That's how the gravitational pulls of the Sun and the Moon work together to create tides in the oceans, so surely it's only reasonable to assume that they must pull on other objects too, creating tidal effects in them as well.
As mentioned earlier, surely they create tides in objects such as human brains.
It's often said that the pull of the Moon affects this organ, creating mood swings (if not full-blown lunacy at the full Moon).
And then there's the womb of course, with its menstrual cycles, which is also said to be affected by the power of the Moon. Even the word menstrual is linked to the Moon - menstrual means monthly, and a month is based to a large extent on the length of the lunar cycle. The word month should really be moonth. It's true that menstrual cycles don't all peek at the full Moon itself, but just the fact of being based on the length of a lunar cycle is a pretty good second best.
It may sound reasonable at first sight to think that these things may be linked to the pull of the Moon, but then, think again... Why are these phenomena only ever associated with the pull of the full Moon? Why is the equally powerful pull of the new Moon, which creates equally high tides as we've just seen, totally ignored? The answer may simply be that it's because the new Moon doesn't make its presence or its power known by shining in the sky (You could say that it's hiding its light under a bushel).
This fact - that the effects of the new Moon aren't factored into the theory that the tides affect human physiology - makes the whole theory begin to look a little shaky.
On top of the glaring omission of the new Moon from the theory there are other factors that make it unlikely to be true.
Just because the gravitational pull of the Moon has a noticeable effect on the oceans doesn't mean that the same applies for small objects. The reason that the tides in the oceans are noticeable is that they are the cumulative effect of the Moon's pull on the whole planet and on an awfully large amount of water. The tidal effect on each cubic inch of water is almost immeasurably small. And the same applies to its effect on brains and wombs.
On top of this, the gravitational effects of the Sun and the Moon on small objects are probably totally swamped by the gravitational pull exerted by relatively large objects that are much closer to hand, such as mountains, buildings or buses.
So, the power of the Moon may not be quite what some of us assume it to be, although it is none-the-less there in its ability to move the earth and the oceans as a whole, with the new Moon being in gravitational terms the equal of the full Moon.
The upshot of this is that any Moon worshippers amongst us who celebrate the power of our satellite by going out at night to dance under the light of the full Moon should perhaps be dancing under the new Moon too. However, if they were to do so they would notice one of the major drawbacks of the new Moon: the dancers would keep bumping into each other in the dark. This would certainly bring home to them the one special power that the full Moon definitely has over all of the Moon's other phases (and especially over the new Moon).
Its light.
In our world of artificial lighting the power of the Moon to illuminate the darkness of night frequently goes unappreciated, but in places beyond the reach of man-made light the Moon makes all the difference between a world that's pitch black at night to one where there's enough light to be able to move around. The brightest phase of the Moon, when it's easiest of all to move around, is of course, the full Moon.
Being able to see at night makes it possible to do many things that would otherwise be impossible: things such as hunting or travelling.
It may even be the light of the Moon that is the force that determines that the length of women's menstrual cycles are about the same as a complete cycle of the Moon's phases. There is some evidence that in the absence of artificial lighting women ovulate at about the time of the full Moon. It's tempting to imagine prehistoric peoples slipping out of their family groups on moonlit nights in search of sexual liaisons with members of other groups - liaisons which would quite possibly result in pregnancy due to the fact that the women were ovulating at the time. (The urge to seek out members of other groups for procreative activities was probably instinctive, as it would lessen the danger of inbreeding.) Maybe this is one reason why the full Moon is instinctively thought of as being romantic.
So, it seems that the really important thing about the Moon is that it supplies us with some light at night. Meanwhile, the importance of its gravitational pull is probably over-rated and is indeed insignificant in terms of everyday human existence (though not of turtle existence, as turtles need the tides).
The Moon's illumination is the product of simple reflection of light off what is essentially a barren sphere of rock - making it in many ways a very mundane source of light.
Yet because of its light the Moon is elevated by many to the status of a semi-mystical entity in the sky, raining strange and mysterious powers down upon the earth. Despite the Moon's intense normalness, it is raised to a level of the supernatural.
This tendency of ours to attribute mystical properties to perfectly normal things such as the giant sunlit sphere of rock that's orbiting our planet has significant consequences when it comes to the way that we interpret the universe and our place in it. Of which more later!
The ultimate message of this chapter is that just because something looks powerful and significant (such as the full Moon) doesn't mean that it is - and just because something goes unnoticed (such as the new Moon) doesn't mean that it isn't.
A final footnote: it's interesting to compare our attitude to the Moon with our attitude to electric light bulbs. The light from the Moon is in many ways much less astounding than the light that's produced by a light bulb, with its legions of excitable subatomic particles darting around and making it glow. The light bulb does after all emit its own light rather than borrowing it from somewhere else. However, no-one attributes semi-mystical properties to light bulbs the way that they do to the Moon. We've become very blase about our electric light bulbs, and electricity in general, in recent years.
