Astrology and the Seventeenth Century Mind: William Lilly and the Language of the Stars (Social and Cultural Values in Early Modern Europe) by Ann Geneva, http://www.amazon.com/dp/0719041546/ref=cm_sw_r_pi_dp_Twtgrb1742EF8
Rudolf II Astrology and alchemy were mainstream science in Renaissance Prague, and Rudolf was a firm devotee of both. His lifelong quest was to find the Philosopher's Stone and Rudolf spared no expense in bringing Europe's best alchemists to court, such as Edward Kelley and John Dee. Rudolf even performed his own experiments in a private alchemy laboratory.
This instrument is clear evidence of the links between the astrolabe and astrology. On one side is an astrolabe for a single latitude, and on the other an astrological volvelle, used to find the positions of planets and other celestial bodies, especially in relation to the traditional astrological houses.