Flat Earth: The Birth of Modern Astronomy #5

Astronomer Copernicus or Conversations with God
Artist: Jan Matejko (1838–1893), Date of Completion: 1873, Collection: Jagiellonian University Museum, Kraków, Poland

Science in the Modern Age

In the Modern Age, science broke away from the theological and authority-based thought systems of the Middle Ages, developing into a structure based on observation, experimentation, and mathematical proof. This transformation, which began with the Renaissance, reached its peak in the 16th and 17th centuries with the work of scientists such as Copernicus, Kepler, Galileo, and Newton. Whereas in the Middle Ages the writings of Aristotle and Ptolemy were accepted without question, in the Modern Age nature was viewed as a book written in mathematical language and examined through systematic experimentation. The scientific method that developed during this period, with its focus on the experimental verification of hypotheses, broke completely from the scholastic method of the Middle Ages.

In astronomy, this revolution was even more striking; beginning with Copernicus's 1543 work On the Revolutions of the Celestial Spheres, the Ptolemaic model, which placed Earth at the centre of the universe, gave way to the heliocentric (sun-centred) system. The medieval understanding of the heavens, governed by geometric constructs rather than perfect circles, crystal spheres, and physical principles, was completely transformed by Kepler's elliptical orbits and mathematical laws, Galileo's observations through the telescope (Jupiter's moons, the phases of Venus, the mountains of the Moon) and finally Newton's law of universal gravitation. The medieval understanding that celestial events were governed by different rules than events on Earth was shattered; in the modern era, the idea of universal physical laws applicable everywhere in the universe took hold, and mathematics, observation, and experimental evidence became the fundamental basis of science, replacing the authority of sacred texts.

The Architects of the Astronomical Revolution

The Astronomical Revolution, or Copernican Revolution, refers to the fundamental transformation in cosmology and astronomy that took place throughout the 16th and 17th centuries. This revolution led to the overthrow of Ptolemy's geocentric (Earth-centred) model, which had been accepted for over a thousand years, and its replacement by the heliocentric (Sun-centred) model. Initially proposed as merely a mathematical hypothesis, this model was gradually supported by observational evidence, discoveries made with the invention of the telescope, and the development of physical theories. This revolution was not only an astronomical change but also an intellectual break that transformed humanity's perception of its place in the universe and the foundations of scientific methodology.

Nicolaus Copernicus (1473-1543), the first architect of this revolution, argued in his 1543 work ‘On the Revolutions of the Celestial Spheres’ (De Revolutionibus Orbium Coelestium) that the Earth was not the centre of the universe, but one of the planets revolving around the Sun. Born in Poland and a clergyman, physician and astronomer, Copernicus was troubled by the mathematical complexity of the Ptolemaic system and sought a simpler and more aesthetic model. His system explained the movements of the planets more simply by removing the Earth from the centre and placing the Sun there instead. However, Copernicus could not completely break away from the paradigm of his time, contenting himself with reducing epicycles while retaining circular orbits. His work, published on his deathbed, did not have a huge impact during his lifetime, but it sparked a revolution for future generations.

Galileo Galilei (1564-1642), the second architect of the astronomical revolution, made revolutionary observations by pointing the telescope he developed in 1609 at the sky. In his work ‘Starry Messenger’ (Sidereus Nuncius), the Italian physicist and astronomer described the mountainous structure of the Moon, the moons of Jupiter, the phases of Venus similar to those of the Moon, and the Milky Way as consisting of thousands of stars. These observations dealt a heavy blow to the Aristotelian understanding that celestial bodies were ‘perfect’ and ‘unchanging,’ and Venus's phases could only be explained consistently with the Copernican model. Galileo's defence of the Copernican model brought him into conflict with the Catholic Church, and in the famous trial of 1633, he was forced to recant his views. However, his observations and the mechanical theories he developed formed the observational basis of the Copernican system.

Portrait of Galileo Galilei
Artist: Justus Sustermans (1597–1681), Date of Completion: circa 1636, Collection: Uffizi Gallery, Florence, Italy

Johannes Kepler (1571–1630), the third architect to complete the mathematical structure of the revolution, formulated three fundamental laws describing the motion of the planets using Tycho Brahe's precise observations. In his works, ‘New Astronomy’ (Astronomia Nova, 1609) and ‘Harmonies of the Universe’ (Harmonices Mundi, 1619), Kepler demonstrated that the planets revolve around the Sun in elliptical rather than circular orbits (First Law), that equal areas are swept out in equal times (Second Law), and that the cubes of the orbital periods are proportional to the squares of the mean distances from the Sun (Third Law). With his approach seeking mathematical harmony and physical causes, Kepler grounded the revolution initiated by Copernicus in a physical basis, paving the way for Newton's law of universal gravitation. His understanding of elliptical orbits represents a definitive break from the Greek cosmology based on perfect circles.

Heliocentric (Sun-Centred) Model

The heliocentric (sun-centred) model is a cosmological system in which the Sun is at the centre of the universe and the planets (including Earth) revolve around it. This model was proposed in the 16th century by Nicolaus Copernicus in his 1543 work ‘On the Revolutions of the Celestial Spheres,’ challenging the geocentric (Earth-centred) model that had been accepted for over two thousand years. In Copernicus' model, the Earth was reduced to the status of an ordinary planet, revolving both around its own axis and around the Sun, initiating a paradigm shift that was revolutionary from both a scientific and philosophical perspective.

Johannes Kepler significantly developed Copernicus' model, discovering that the planets move in elliptical rather than circular orbits and that their speeds vary according to their distance from the Sun. The three laws he presented in his works published in 1609 and 1619 (elliptical orbits, equal areas in equal times, and the relationship between the cubes of orbital periods and the squares of distances) could describe the movements of the planets with great mathematical accuracy. Galileo Galilei, meanwhile, provided important observational evidence for the heliocentric model with his groundbreaking observations through a telescope in 1610 (the phases of Venus, the moons of Jupiter, the mountains on the Moon's surface).

The heliocentric model gained its physical foundations with the universal law of gravitation and the laws of motion set out by Isaac Newton in his 1687 work ‘Principia’. Newton explained the reason for the planetary motions mathematically defined by Kepler, making the heliocentric model a scientific reality. These physical theories strengthened the consistency of the model by explaining why planets revolve around the Sun and how they remain in their orbits.

The heliocentric model was ultimately confirmed in subsequent centuries with the advancement of observational technology. In 1729, James Bradley discovered the aberration (deflection) of starlight, providing indirect evidence of the Earth's motion, while in 1838, Friedrich Bessel directly proved that the Earth revolves around the Sun by measuring the parallax of the star 61 Cygni. In 1851, Léon Foucault's pendulum experiment visibly demonstrated the Earth's rotation on its axis. These observational proofs, combined with physical evidence such as the bulge at the equator and the Coriolis effect, conclusively proved the accuracy of the heliocentric model.

The acceptance of the heliocentric model symbolises not only a transformation in astronomy but also in the scientific method. The modern understanding of science, based on observation, experimentation, mathematical consistency, and critical thinking rather than authority and tradition, took shape with this revolution. The transformation of the Earth from the centre of the universe to an ordinary planet shook the anthropocentric worldview and laid the foundations for modern scientific thought and the Age of Enlightenment. Today, the heliocentric model is accepted as part of broader galactic and cosmological models and accurately describes the fundamental structure of our solar system.

Features of the heliocentric model:

1. The Sun is located at the centre of the system (or near the centre).
2. The planets (including Earth) revolve around the Sun.
3. The Moon revolves around the Earth as its satellite.
4. The Earth rotates around its own axis daily and revolves around the Sun annually.
5. The orbits of the planets are elliptical, and the Sun is located at one of the foci of this ellipse (Kepler's 1st law).
6. The planets accelerate as they approach the Sun and decelerate as they move away (Kepler's 2nd law).
7. The squares of the orbital periods of the planets are proportional to the cubes of their average distances from the Sun (Kepler's Third Law).
8. The motion of the planets is governed by the universal law of gravitation (Newton's contribution).
9. The apparent retrograde motion of the planets is simply explained as a perspective effect caused by the Earth overtaking planets that are moving faster or slower.
10. The lack of parallax motion in fixed stars is explained by their great distance from the Solar System.
11. The seasons are explained by the tilt of the Earth's axis and its rotation around the Sun.
12. Venus and Mercury always appear close to the Sun, and their full phases can be observed relative to Earth.

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