Passion of the People – 1.1.6

The Legacy of the Greek and Roman Antiquity

The early Greeks watched the sky very closely. Greek farmers used the positions of the sun and stars to plan and organize agricultural chores for each season. Greek sailors used the stars to guide their navigation. The Greeks’ main contribution to astronomy, however, was their effort to explain what they saw. They did more than merely observe and record the movements of the heavenly bodies. They sought to understand why and how those bodies moved in such an orderly and predictable way. In doing so, the Greeks transformed stargazing into a science.

Greek astronomers spent little time wondering about what the planets were made of or how they came into existence. Instead, they wanted to find a logical, orderly system for predicting the movements of the Sun, Moon, and planets. They looked to mathematics and geometry to help discover such a system. In the 300s B.C., a mathematician named Eudoxus proposed a theory about the movement of the Sun, the Moon, and the planets suggesting that each heavenly body was fastened to the inside of a series of concentric spheres, with the Earth at the center. The spinning of the spheres made the planets move. Eudoxus’s theory failed to explain all celestial movements, however, and other Greek thinkers tackled the problem.

Around 270 B.C., the mathematician and astronomer Aristarchus correctly suggested that the Sun, not the Earth, is at the center of the planetary system. He also suggested that the Earth moves around the sun like the other planets, and that it rotates on an axis. Most ancient thinkers did not believe that the Earth moved, so they rejected Aristarchus’s ideas.

More than a century later, in about 150 B.C., the astronomer Hipparchus developed a theory of celestial movement based on the geometry of circles. He suggested that the sun and the moon moved around the Earth in circular paths, or orbits. To explain why celestial movements are not perfectly regular or symmetrical, Hipparchus theorised that the Earth was not exactly at the center of the orbits, or that the orbits themselves moved in complicated patterns. Hipparchus also compiled a star catalogue that listed 850 stars and gave the location of each in the sky.

The most influential astronomer of the ancient world was Ptolemy. He was born in Egypt in about 90 AD, when the Romans were ruling Egypt. He was a Roman citizen. Ptolemy accepted Hipparchus’s theory and used his own observations to expand it. Ptolemy also produced a star catalogue that listed over 1,000 stars. His view of the Universe was accepted by astronomers throughout the Mediterranean world, and it remained the foundation of astronomy for more than 1,000 years after his death.

One of the best-known manifestations of Roman astronomy is the Julian calendar. It evolved initially from a simple sequence of indigenous festivals related to the farmers’ seasonal year, then became increasingly formalised as Roman society became increasingly urbanised. At first the civic calendar was based on the phase cycles of the moon, but it faced increasingly serious problems in getting out of step with the seasonal year because of political interference in the process of intercalation. All this culminated in 45 BC in the switch from a lunar to a solar calendar, dividing the year into twelve “months” that were in fact completely independent of the Moon.

Astronomy played a significant role in many aspects of Roman life. Land surveyors, employed all over the empire with simple instruments, needed good astronomical knowledge: this is clear from surviving surveyors’ manuals. Other topics instruct the navigators of commercial ships in navigating by the stars. Sundials were in common use for telling the hour of the day: over thirty were recovered in Pompeii alone.

Astrology, popular among the Romans’ Etruscan predecessors as well as in Hellenistic Greece increased greatly in popularity in the second century CE with the rise of mystery cults such as those of Isis and Mithras. These were astral religions, and for many people the Sun itself became an object of direct worship. Later, these cults came into direct conflict with Christianity.

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Passion of the People

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Greek temple and night sky – Image by RENE RAUSCHENBERGER – Pixabay

Greek temple in Sicily – Image by RENE RAUSCHENBERGER – Pixabay

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Ancient Roman astronomy