Why and How - A traditional view
I am not claiming that the following explanation is 'THE' explanation - it's one that Sue Ward advanced and for me it added one or two insights into the whole divinatory process and it does see Astrology literally as divination - learning the mind of God.
This is a summary, with occasional comment of a talk she gave called 'God, the Universe and Everything' and the full transcript can be downloaded in pdf form from her website.
www.sueward.co.uk in the Articles section. Even in a shortened version, it's quite long but I think it provides a good basis to understand early Western Astrology.
The explanation starts from the position that Astrology has been separated out from the other Hermetic sciences - Magic, Alchemy and the Qabala and also from its oral tradition - which is not the case elsewhere. So in a real sense, Sue is trying to 'reconstruct' a basis which recognises those ideas and philosophies - to reconnect Astrology to it's spiritual background as a true divinatory art. Now I know that many Modern Astrologers in the West would bristle at that. The Astrological Association of Great Britain, sees Astrology as having no connection to the psychic, the religious, or the spiritual, as an essential part of it's nature - Atheists can practice perfectly good Astrology.
Sue goes on to say that Astrology is a system of correspondences - not only in the Hermetic saying of 'As Above So Below' but to the extent that Astrology corresponds to Nature - Mars corresponds to War, for example and War corresponds to Mars - be it a violent War or an argument - a War of words.
If Astrology corresponds to Nature - so do humans - the microcosm of Nature's macrocosm. So the correspondence of Astrology to nature also brings the correspondence of Astrology to humanity - As Above, So Below In classical and medieval times, even through to the seventeenth century, Science was based in hermeticism so Astrologers could prove the truth of Astrology in their own terms not just take it on trust.
We can see he Astrological correspondence to Nature through the biblical creation story (and indeed through the creation stories of other cultures) -
'In the beginning God created theHeaven and the Earth; And the earth was without form and void and darkness was on the face of the deep'
And God said let there be light And there was light. and God saw the light and saw that it was good. and God divided the light from the darkness And God called the light Day and the darkness Night'.
Light, Day and Night were fundamental to the early Western approaches to Astrology - Diurnal and Nocturnal charts were treated differently - as they reflect God's creation.
Genesis goes on to show God creating a firmament in the heavens and separating dry land from the sea and then putting lights in the firmament
'to divide day from night and let them be for signs and seasons and for days and for years'
The lights are the visible planets and comets and the signs are omens. However the lights also provide the seasons and measure time - the role of the planets as Chronocrators - rulers of time.
Genesis continues with God making two Great lights one to rule the Day and one to rule the Night - Early Western Astrology sees the Sun as ruler of Day charts but the Moon as ruler of Night charts and also classifies the other planets as Diurnal or Nocturnal.
The story of Genesis has two twofold divisions - Light and Dark (Day and Night) and Above and Below (Heaven and Earth or Land and Water) We could see this as the sphere divided into four equal parts - and thus the four Cardinal points. We could also see Light as bringing Heat, Darkness bringing Cold, Earth bringing Dry and the Waters bringing moisture - the four key building blocks of early Western science and embodied in much of traditional Astrological explanations and methods.
These four, Light/Heat, Darkness/Cold; Earth/Dryness and Water/Moisture are the conditions necessary for fertility and therefore life - 'And God said let the Earth bring forth grass, the herb yielding seed' - life had begun. Even today we recognise the importance of photosynthesis to life and that the conditions need to be just right - not too hot, not too cold, not too dry, not too wet - both life and Astrology seek a balance - 'Nothing in excess' to quote another Western tradition.
Incidentally this explanation also shows why the Tropical Zodiac gained prominance - From the beginning, the role of the Sun and planets is to regulate the seasons.
From the seasons come the oppositions of Winter and Summer, Spring and Autumn and the rulerships of the Astrological sign and we can take it further to derive a comprehensive philosophy of Astrology but that goes beyond the scope of this thread.
Now despite the fact that I'm not a religious person (like Sue) it's important to labour the point - Astrology WAS seen as a divine Art in a divine system of creation - it is not an adjunct it is central to understanding existence. The only way that Astrology might fail is through the Astrologer, who is only human - he or she needs to be properly trained - not to purvey a standard system (Astrologers were nowhere near as united as priests in their doctrines)- but to learn and reflect on the sciences of the day and to understand the interconnection of all nature.
From the late Seventeenth Century onwards, we have become increasingly secularised in the West and Science has become increasingly compartmentalised. So the modern Western Astrologer must look elsewhere for an answer or be seen as a 'crank' - Does it lie in genetics, gravity waves, or other form of radiation...?
Can we accept a theory which relies on God and Creation or must we turn to something in line with modern science. Can we have a science of Asrology that provides answers through empirical research - such as the Gauquelins.
Over to you