Final answer:
The simplest horoscope is a chart that shows astrological positions of celestial bodies at one's birth, which is used for natal astrology. This detailed system differs from generalized sun sign astrology, with interpretations based on traditional but complex rules.
Step-by-step explanation:
The simplest horoscope consists of a chart that reveals the positions of the Sun, Moon, and planets within the zodiac signs and the sky at a specific moment, often corresponding to an individual's birth time. The horoscope functions as a 'marker of the hour,' reflecting ancient Greek origins from the words 'hora' and 'skopos.'
Astrologers chart the locations of these celestial bodies and their placement in 'houses' which shift due to the Earth's rotation, affecting the zodiac's movement across the sky. The process, originally formulated nearly 2000 years ago by Ptolemy, continues to be used today, with interpretations based on established but artful rules from texts such as the Tetrabiblos.
While advanced software has simplified the casting of horoscopes, the practice is still rooted in traditional principles. The natal astrology, which includes this detailed charting, is distinct from the more generalized sun sign astrology commonly found in media, which only categorizes individuals into 12 groups based on their sun sign.
Finally, the interpretation of a horoscope is intricate, involving many astrological schools of thought, with specific predictions often varying between astrologers despite the use of standardized rules.