Beginnings of the Scientific Revolution

Moons that should not exist

In January 1610, the Italian mathematician Galileo Galilei pointed a telescope he had built at Jupiter. Night after night he saw four small "stars" beside it that changed position. He concluded they were moons orbiting Jupiter. That was a problem for the accepted picture of the universe, in which everything circled the Earth.

His little book Sidereus Nuncius (The Starry Messenger, 1610) sold out quickly. Within twenty-five years he would be on trial in Rome. This lesson explores how new ways of studying nature began between 1450 and 1650. (The story continues with Newton and the Enlightenment in the sibling unit The World, 1650–1789.)

The old picture

Most educated Europeans, Muslims and Jews in 1500 relied on the ancient Greek thinkers Aristotle and Ptolemy, as developed by medieval Islamic and Christian scholars:

• Geocentric universe: the Earth sits still at the centre; the Moon, Sun, planets and stars move around it in perfect circles.
• Heavens versus Earth: the heavens were perfect and unchanging; the Earth was the place of change and decay.
• Medicine: the Roman physician Galen taught that health depended on balancing four humours (blood, phlegm, yellow bile, black bile).
• Method: knowledge came mainly from authoritative texts and logical reasoning from them.

This system was not foolish: it explained everyday observations (the Sun does seem to move) and made workable predictions.

Astronomy beyond Europe

Astronomy was a global science:

• In Samarkand, the Timurid ruler Ulugh Beg built a great observatory in the 1420s and produced a star catalogue of high accuracy.
• Astronomers of the Maragha observatory in Iran (1200s), such as Nasir al-Din al-Tusi, devised mathematical models to fix problems in Ptolemy's system. Very similar devices appear in Copernicus's work; historians still debate whether he learned of them from earlier Islamic work (and if so, how) or reached them independently.
• In Istanbul, Taqi al-Din built an observatory in 1577; it was demolished in 1580 after religious and political opposition.
• In Ming China, the Jesuit Matteo Ricci and the scholar-official Xu Guangqi translated the first books of Euclid's geometry into Chinese (1607), and the court later used Jesuits to reform the calendar.
• Earlier Mesoamerican peoples, including the Maya, had tracked Venus and eclipses with great precision.

Key steps, 1543 to 1637

• 1543: Nicolaus Copernicus, a Polish cleric, published On the Revolutions of the Heavenly Spheres, arguing that the Sun, not the Earth, is near the centre and the Earth orbits it. He still used perfect circles. Few people accepted it at first.
• 1543: Andreas Vesalius published On the Fabric of the Human Body, based on his own dissections, with superb printed illustrations. He showed that Galen, who had dissected mainly animals, made errors about human anatomy.
• 1572 to 1601: Tycho Brahe made the most accurate naked-eye observations ever; a new star (a supernova) in 1572 suggested the heavens could change.
• 1609 and 1619: Johannes Kepler, using Tycho's data, showed that planets move in ellipses, not circles, and found mathematical laws for their motion.
• 1610: Galileo reported mountains on the Moon and moons around Jupiter; soon after, he observed the phases of Venus, which fit a Sun-centred system but not Ptolemy's.
• 1620: Francis Bacon argued in Novum Organum that knowledge should be built by careful observation and experiment, reasoning upward from many facts (induction).
• 1628: William Harvey showed that the heart pumps blood in a circuit around the body.
• 1637: René Descartes, in Discourse on the Method, argued for doubting everything not certain and reasoning step by step from clear first principles (deduction), using mathematics.

Galileo and the Church

Galileo argued openly for Copernicus. In 1616 the Catholic Church declared the idea that the Earth moves to be contrary to Scripture and warned Galileo not to hold or defend it. In 1632 he published the Dialogue Concerning the Two Chief World Systems, which seemed to mock the geocentric view. In 1633 he was tried by the Inquisition, forced to recant (publicly reject) the idea, and kept under house arrest until his death in 1642.

Historical perspective: it is easy to tell this as "science versus religion". Historians show it was more complicated: many churchmen were astronomers and some supported him; Galileo's proofs were not yet conclusive; the trial happened during the Thirty Years' War and Counter-Reformation fears about authority, and Galileo had offended a former ally, Pope Urban VIII. The Catholic Church formally acknowledged its errors in the case in 1992.

Why "revolution"? A debated label

The term Scientific Revolution suggests a sudden, complete break. Some historians reject it: change took 150 years or more; leading figures also practised astrology and alchemy (Kepler cast horoscopes; Newton later studied alchemy); and many ideas built on Islamic and medieval scholarship. Others keep the term because the period truly changed how knowledge was made: by observation, experiment, mathematics and printed sharing of results. Either way, by 1650 the old certainty that ancient authorities were right had been broken.