The Top 7 Best-Selling Astrology Books by Gary Goldschneider and Joost Elffers Date of publication: October 31, 2013 (reprint), October 1, 1998 (original) Amazon rating: 4.5 stars Pages: 832 Who this book is for: Someone who is looking for a greater understanding of his or herself, based on his or her birthday Gary Goldschneider, bestselling author of “personology” and astrology books, studied the life stories of more than 20,000 people over a time span of 50 years to uncover traits and descriptions published in his three books. The Secret Language of Birthdays reveals the personality traits between people who share the same birthday through “personology” and the analysis of thousands of profiles. Personology refers to the characteristics influenced by the sun, sign, season and day. The book is based on the theory that life is cyclical, meaning that people that share the same birthday, have the same characteristics. Each day of the year is featured on a double-page spread with a personality description, health information, important numbers and tarot cards.