—Ralph Waldo Emerson
Astrology is the science that relates planetary patterns measured by positions in the sky and mapped in relation to the physical location and time of birth of a person or an event in a very long tradition of observation and interpretation to describe the character of the person or event.
While often considered as an ancient form of divination, it is today used as a scientific approach to self-understanding and the forecasting of mundane events: weather and climate changes, earth movements, economic and political events, and cultural trends. The horoscope provides a "map" of planetary energies at any specific time and as projected at a particular location. That map is correlated with the meanings of those planetary energies as established through thousands of years of observation and the now established principles of horoscopic analysis and interpretation.
A horoscope calculated for the exact moment and place of birth a like a photograph taken of the complex relationship of planetary forces as reflected in the astral body. Since the astral is formative to the physical, this photograph tells the tale of the physical incarnation and of the Personality. Solar Return (birthday) horoscopes show the annual progression from the birth chart.
This scientific astrology has little to do with the simplistic "birth sign" horoscopes found in popular media which lumps together approximately 1/12th of the population as alike based purely on the position of the Sun in a particular zodiacal sign on their birthday. Thus, while there are some general similarities commonly shared by those of the same Sun Sign, there are nearly as often powerful planetary factors involved providing a substantial deviation from some of the generalities.