daphne
Well, its a fairly old tradition that the patterns present in the cosmos relate to ones that unfold during our lives. 'Why we would do this' - is to examine and study, to gain insight and understanding of ourselves - The first hermetic axiom is 'know thyself'.
Why turn the natal chart back 28 deg ( I am not sure of the current exact amount) ?
Unless it is a sidereal chart (based on the actual positions of the stars- like all other culture's astrological calculations / charts ) it wont accurately show the celestial relationships. Basically the earth wobbles like a spinning top slowing down, this causes the position of the Sun (in relation to the back drop of stars) to move 1 degree every 72 (I think)* years 'backwards' through the zodiac. Since the western astrological tables (ephemeris) was calculated ... (around 300 AD ... sorry for all the approximations ... going off memory here) the zodiac has moved nearly 1 full sign from what it says in the ephemeris.
Tropical astrologers will come up with all sorts of reasons why and tell you I am wrong, or I dont understand , etc. ..... whatever <shrug> you can argue with me but its a bit much to argue with the rest of the world, history and NASA ( as the source of actual star / planet locations) though . Of course, if all the info is published in a book of tables that us smart westerners have been using for over 2000 years .... we cant have been wrong ... I am sure we can come up with a reason to explain how we are right and the Universe is wrong
* for LRichard ... 50.2 arc seconds per annum some nice equations in here for you ;
http://en.wikipedia.org/wiki/Axial_precession
Addit : ..... precession is what brings about concepts like 'The Age of Aquarius'.
Thank you for the explanation. If I understand correct what you said, astrology now use an outdated system to calculate birth charts, right?
I have no knowledge about the matter, but it sounds revolting that there is no info about this error and a wrong calculus is processed. It is the first time I read about this correction. Do you have some suggestion for further read, maybe some astrology books that promote the necessary corrections?