The Sabian Symbols

All Levels
Divinatory, Interperative

This isn't exactly about the machanics of astrology, but on the periphery and still very, very cool. Sabian Symbols were created in 1925 in a single day in a park in San Diego in which an astrologer presented each degree of the zodiac, one by one, to a clairvoyant who then described an image she saw.
You can look up the degree of every placement in your chart to paint a full, psychedelic picture of your personality. You can also look up the degrees of New and Full Moons or other transits to get another perspective on what they might mean. They're a divination tool like tarot cards, and can bring a much-needed poetic immediacy when astrology feels a little too math-y.