Mayan astrology

The Tzolk'in is formed by combining 20 day signs with the numbers 1 to 13: 20 x 13 = 260. Each day is named by both a sign and a number (for example, 4 Ahau), and the same combination recurs every 260 days. No one knows for certain why this number was chosen. Explanations such as the length of human pregnancy, the cycle of Venus and the agricultural calendar have been proposed, but none has been confirmed. When the Tzolk'in and the Haab' run together, the same combination of days comes around again only once every 52 years; this is called the Calendar Round.

The 20 day signs are drawn from animals, natural phenomena and concepts: Crocodile, Wind, Night, Seed, Serpent, Death, Deer, Star, Water, Dog, Monkey, Road, Reed, Jaguar, Eagle, Owl, Earth, Flint, Storm and Sun. The 13 tones set the numerical quality of the day. Each number has a name in the Mayan language, and the tone is read as a measure of the stage the sign's energy has reached. The inscriptions contain no horoscope reading in today's sense. The personality interpretations here draw on the K'iche' daykeeping tradition and on modern interpreters, while the meanings of the tones are largely a modern interpretation.

To find your Mayan sign, your date of birth is converted into a day in the Tzolk'in. The calculation uses the Julian day number of your birthday and the number of days elapsed since a fixed reference day. Dividing this number by 13 gives the tone number as the remainder, and dividing it by 20 gives the day sign. The reference is the GMT (Goodman-Martínez-Thompson) correlation, the one most widely accepted in academic circles; under this correlation, 21 December 2012 is 4 Ahau. Sources that use different correlation constants, or the Dreamspell system developed in the 1990s, may give different results.