Many people religiously consult the astrology section of their favourite newspaper, magazine or website, eagerly anticipating the good news that the stars hold for them. But do these 'predictions' amount to anything serious, or are they just a form of harmless entertainment?
Let's start with the first of the customary accusations levelled against astrology - that it's vague. If you consult your "reading" for today, and substitute the word "you" in the reading, say, for your mom's name, or your best friend's, you will probably find that the "reading" is largely accurate for them, too. Dawkins did a superficial experiment with a small sample of people - he took a reading, told people it was for their star sign, whereas it was in fact for another sign - and then asked them what they thought. Many of the people found it to be fairly accurate, except one person: the person whose sign it was. Surely if the reading were accurate, it would only ring true for the person whose sign it was?
But does astrology even pretend to be a form of prediction? Well, unfortunately, yes. The system was originally based on the observation that regular human events seemed to correlate with observed celestial events, and so when these celestial events recurred, the human events were expected to recur. But astrologers argue that there is more to those 'predictions' that they make. A true astrologer argues that these 'predictions' are actually an indication of possibilities or potentials, likelihoods or probabilities. Astrology is more of a mapping system, which correlates stars and planets to personality types, tendencies, upbringing, the way you will probably be in a relationship, your potential for money earning, and so on. One can look at it in the same way that one would look at a psychological profile. So persons with specific celestial mappings, which can be quite unique, could be said to have certain patterns happen in their lives. Astrology is not, moreover, just a simple matter of the star signs determining the personality. There are other aspects that have to be taken into account, such as planets. A more accurate, true prediction or characterisation, could only be drawn from consulting a Birth Chart. This alone, then, could give an indication of the kind of life you could expect, or events that are likely to happen. Astrology is not, therefore, predictive in the sense that it tries to give precise descriptions of forthcoming events. Rather, it just gives tendencies of your personality, and thus, the kinds of things that are likely to happen to you. The predictions one sees in the newspapers are certainly not meant to be accurate, a true astrologer will argue, because they do not take all the factors into account, such as the relevant planets, your family, and so on. They are very broad, at best. They are more for entertainment purposes.
But how could astrology be accurate at all? What about a case of two people with the same star sign, who have radically different fates and personalities? My stepfathers shared a birthday, but you could not imagine two people with such different fates and personalities. How is that possible in the light of Astrology's claims? Well, the astrologer answers, this case would be one in which the ascendant planets were very relevant, and explained the difference. Suppose we accept that reply. But then what about the case of twins? Twins do not often share the same fate or personality. Yet they should always have identical fates, if astrology were true.
Suppose, now, that astrology admits that it has some predictive tendencies, given that it lavishly tells you in the newspapers what is going to transpire on any particular day. How accurate are these 'predictions'? In the scientific arena, we consider a prediction accurate only if it gives precise details. Scientists discard any theory that does not predict accurately. Remember, when you step on a plane, that you're putting yourself in the hands of [Bernoulli's principle](http://en.wikipedia.org/wiki/Bernoulli%27s_principle#Real-world_application). It predicts very accurately, statistically speaking. How accurate, by comparison, are astrology's predictions? When they say that you are going to "have difficulties with money today," why do they not say "you will lose exactly £10 out of your wallet at this exact address..." They ought to, if astrology were remotely a science.
Now, let's look at the method of astrology. Astrology is not, contrary to what most people assume, a question of which constellation was in the sky at the time of your birth. It also involves the relative positioning of planets and the moon as well as stars and sun, as we’ve mentioned. The time of birth has a big impact, not just the day of birth. There are planetary alignments to consider as well. As such, astrology is a sophisticated system. But the important question is this: do astrologers use telescopes? If not, they cannot possibly obtain an accurate reading - because if they did use telescopes, they'd notice that the constellations that they're expecting to see, are not actually the dominant ones at that point in time. Since Ptolemy first devised our current system, the stars have shifted about 23 degrees. That's an entire star sign! If astrologers bothered to use telescopes, they'd have noticed this. But astrologers use charts, not telescopes. Usually the Earth is central on the chart, and the Sun is a mere planet that orbits the Earth. We last gave the geocentric model of the cosmos credence hundreds of years ago; we now know it to be false.
Third, let's think about the mechanism by which the stars could influence us. Traditionally, no specific energy or causal mechanism is stipulated as the reason for the correlations between star signs and personality or fate; they are merely observed correlations lacking an explanation. So how do the stars and planets influence us? Could it be by means of light? Well, that won't work, because the planets are so dim that the light coming from them will have less influence on us than an LED on your computer screen. That's right - if you're pregnant, and light is the way that the stars influence us, then you're messing with your unborn baby's future by sitting near any artificial light source.
If, however, it's not light, then maybe it's gravity. Well, anyone who's done Physics will recognise the equation F = G(M1M2)/r2. This equation measures the force of gravity between two objects. Let's take an example. Let's try the influence of Jupiter. I don't want to prejudice this by using, say, a star, because stars are much further, and therefore their influence is less. The mass of Jupiter is 1.8986×1027 kg - roughly two billion billion billion kilograms. Let's say a newborn's mass is 3kg (and G is a very small constant). The distance between the baby and Jupiter is between 893 billion and 964 billion metres apart, depending of the positions of the two planets in their orbits. If we do the calculation, it gives us a force of 0.0000004088147 Newtons. For the case of distant stars, it's much worse, since they're thousands to millions of times further away. Now, just so that you understand how weak this force is, the force that 1 Lb of mass exerts on earth is 4.48 N. The force Jupiter exerts on us here on Earth, therefore, is about ten million times less than a 1 Lb weight. No chance that that could mess with your fate; the gravitational field of your mother probably has more influence.
But perhaps the stars exert their influence on us by means of a yet-unknown force. Perhaps there's a mysterious force in the universe - let's call it the Force - that influences us. And let's say that the Force is much stronger than gravity, and therefore, can reach us from these stars and planets, and influence us. Surely, if the Force is strong enough to reach us from planets that are billions of miles away, and surely if it is strong enough to exert a fatalistic or deterministic force on our minds and bodies, it could be detected and measured? Surely, by now, we'd have noticed strange things happening, and developed a way to measure it? We can measure very small things indeed - such as the force of gravity, the fields of particles, and so on. So can we not suppose that something as powerful as this Force would set of alarms in laboratories world-over? And surely the Earth would also have this Force, and completely overrule the other planets purely on the basis of its proximity? You can't debate this one; all forces diminish in strength over distance, as the formula above illustrates. This means that the Earth must be millions of times more dominant or ascendant for everyone in their Birth Chart.
It has been found that there are seasonal effects on personality (google this), but remember that unlike the stars, seasons vary between hemispheres; so even if astrological predictions about personality worked for the northern hemisphere, they’d be completely opposite for the southern.
Lastly, why should the stars at the _time of birth_ be relevant? Does it not make sense to suppose that the measurement should be from the time of _conception_? Logically, the stars and planets cannot exert a fatalistic influence on an already-existing being. Is this not the key reason why we talk of someone being a Scorpio or an Aries - because they were influenced by those constellations _at the time of their birth_? But that doesn't make sense. Think about it. If a person, who has already existed for nine months, can be influenced by stars just because he or she happens to emerge out of a warm damp container at that time, then, anyone who gets out of a heated swimming pool is at risk of having their destiny seriously messed with by prevailing constellations at the time. If astrology were true, the Force would influence us at conception, not birth. But an advocate of astrology may have an answer here. Perhaps it is dated from the time of birth because this is the point in time in which forces and events start to come into play in your life, because you are no longer in the safety of the womb. This answer would be a good one if it wasn't well-known that babies are influenced in utero by what the mother does, environmental sounds, and so on. Moreover, how would some distant stars and planets just happen to "know" when you emerged into the world and therefore that they must now start influencing you? Surely they're emanating their Force all the time, regardless of whether you've been born or not? Their influence must start at conception, not birth. The sign at your birth is irrelevant.
I must conclude that astrology is nonsense. But why should I spoil peoples' fun? For a number of reasons. Firstly, there's the self-fulfilling prophecy problem. It is possible that people consulting an astrological reading might subconsciously _act it out_. Someone might read, for example, that they're going to get very bad news that day, and go about the whole day unconsciously doing stupid things because they're so stressed about what the 'bad thing' might turn out to be. Secondly, astrology is part of a superstitious world-view, one that doesn't connect observed facts to theories by an explanatory causal mechanism. Astrology offers no causal link or explanation at all for why "Scorpios" are "belligerent" or "Taureans" are "stubborn". This world-view can cause harm. Think of how astrology encourages stereotyping and unfair treatment - especially when it comes to dating (“Oh I only date Sagittarians, I’m incompatible with Leos”). Imagine if a newspaper wrote articles generalising about a race or nation of people? That paper would be sued for racism. So why is it OK to typecast and stereotype people on the basis of a completely unscientific, unexplained system like astrology? Some people defend astrology as a kind of predecessor of Psychology, as a kind of theory of personality. But Psychology bases its theories on observed behaviour of persons. It does not _prescribe_ behaviour _to_ persons on the basis of their birthdate. ("Oh, you're a Taurus, so you're stubborn". No free choice in the matter at all).
I think it's written in the stars that astrology's days are numbered.