Written in the Stars

At first sight, this depiction of a woman in 17th-century attire looking through a telescope seems to evoke astronomy, the systematic study of celestial objects, motions, and phenomena. The caption (in French) reveals that it actually represents astrology, which seeks to derive the character of individuals and forecast future events from the positions of the celestial bodies in the sky. Astronomy and astrology went separate ways from the 1600s onwards, but until then they had been closely interrelated. 

Shown here is a German calendar from around 1700 showing the connection between days of the week, planets (including the Sun and the Moon), and the respective deities of classical mythology. The doctrine of planetary influence led to the belief that each day has its own ruling planet. This idea is still echoed by the names of the days of the week in several languages, for example: “Montag” (Monday) in German for the day of the Moon; “Martes” (Tuesday) in Spanish for the day of Mars; and “Saturday” in English for the day of Saturn.  

All around the world different cultures developed their own systems of sky knowledge and doctrines to interpret celestial events. Chinese astrologers paid a special attention to the Moon, and in order to keep track of its motion across the sky, they established a framework of 28 celestial divisions called the lunar mansions. They are shown as segments marked with spoke-like lines around the edge of this 19th-century Chinese star chart, which is based on an older chart dating to the 12th century.

This 17th-century illustration depicts the idea of a harmonious cosmos that emerged in Ancient Greece, and lies at the core of Western astrology. The Earth sits static at the center, surrounded by concentric moving spheres, each carrying a planet. The outermost sphere carries the so-called fixed stars, including the zodiac constellations. On the basis of this concept, Greek scholars developed geometrical models to describe and predict the celestial motions, which provided astrology with a scientific basis. 

Shown here is an example of a horoscope from a 15th-century astrology treatise by Johannes Angelus. The 12 triangular divisions are the so-called houses, which correspond to specific domains of human life such as relationships, honors and reputation, health, etc. Depending on the place, date, and time of a subject’s birth, the various houses will be populated by different zodiac signs and planets, with varying meanings as to the character and fortunes of the subject. According to Angelus, this was the horoscope of a man argumentative and annoying as a dog. 

“Zodiac Man”, a type of diagram of the body, served as a visual aid to medieval physicians. It is based on the concept that each area of the body is ruled by a certain zodiac sign and influenced (favorably or unfavorably) by the planets that happen to be in that sign at a given time. For example, the diagram shows that Aries rules over the head. Thus a physician preparing an intervention on a patient’s head would investigate what planets were in Aries before proceeding. The presence of the Moon would be seen as adverse and lead to postponing the procedure. 

By the late 18th century, astrology was generally dismissed in intellectual and scholarly circles as bogus science. But astrologers still found a clientele for their services, and astrology went through a revival. This device was likely made in France around 1800 and speaks to that renewed interest in the subject. It includes two sets of discs and pointers stacked together, each designed for casting a horoscope. The astrologer could thus compare a pair of horoscopes at a glance and advise, for example, on the compatibility of two subjects for marriage.