8.1 Copernican Revolution and the New Cosmology

The Copernican Revolution shook up our view of the universe. Copernicus put the Sun at the center, not Earth. This challenged centuries of belief and faced resistance from the Church and scholars.

Kepler built on Copernicus's work, using Tycho Brahe's data to refine the model. He discovered planets move in ellipses, not circles, and formulated laws of planetary motion. This new cosmology transformed astronomy.

Copernican Revolution

Heliocentric Model Challenges Geocentric Tradition

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• Nicolaus Copernicus, a Polish astronomer and mathematician, proposed a heliocentric model of the universe in the 16th century
• Heliocentric model places the Sun at the center of the universe, with the Earth and other planets orbiting around it
• Challenges the long-held geocentric model, which placed the Earth at the center of the universe with the Sun, Moon, and planets orbiting around it
• Copernicus' ideas were met with resistance from the Catholic Church and many scholars who adhered to the traditional geocentric view

Publication of De revolutionibus orbium coelestium

• Copernicus' major work, De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres), was published in 1543, the year of his death
• Presented mathematical calculations and observations supporting the heliocentric model
• Argued that the Earth rotates daily on its axis and revolves annually around the Sun
• Proposed that the apparent motion of the heavens is due to the Earth's rotation, rather than the movement of the celestial spheres

Kepler's Contributions

Collaboration with Tycho Brahe

• Johannes Kepler, a German astronomer and mathematician, worked as an assistant to Tycho Brahe, a Danish astronomer known for his precise observations of planetary positions
• After Brahe's death in 1601, Kepler gained access to Brahe's extensive data on planetary motion
• Used Brahe's data to refine and expand upon Copernicus' heliocentric model

Kepler's Laws of Planetary Motion

• Kepler formulated three laws of planetary motion based on his analysis of Brahe's data
• First Law (Law of Ellipses): Planets orbit the Sun in elliptical paths, with the Sun at one focus of the ellipse, rather than in perfect circles as proposed by Copernicus
• Second Law (Law of Equal Areas): A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time, demonstrating that planets move faster when they are closer to the Sun
• Third Law (Law of Periods): The square of a planet's orbital period is directly proportional to the cube of its average distance from the Sun, establishing a mathematical relationship between a planet's distance from the Sun and its orbital period

Cosmological Concepts

Celestial Spheres in Ancient and Medieval Cosmology

• Ancient and medieval cosmology relied on the concept of celestial spheres, which were believed to be concentric, transparent, and crystalline spheres that carried the celestial bodies around the Earth
• Ptolemaic system, developed by the Alexandrian astronomer Claudius Ptolemy in the 2nd century CE, proposed a complex system of epicycles and deferents to explain the apparent motion of the planets within the framework of a geocentric universe
• Medieval European scholars, influenced by Aristotelian philosophy and Christian theology, generally accepted the Ptolemaic system and the idea of celestial spheres

Challenges to the Celestial Spheres Model

• Copernican heliocentric model challenged the notion of celestial spheres by proposing that the Earth and other planets orbited the Sun, rendering the concept of celestial spheres unnecessary
• Kepler's laws of planetary motion, which described the elliptical orbits of planets, further undermined the idea of perfect celestial spheres
• Galileo Galilei's telescopic observations, such as the discovery of Jupiter's moons and the phases of Venus, provided empirical evidence supporting the Copernican heliocentric model and challenged the traditional cosmological view of celestial spheres