Heliocentric System

Nicolaus Copernicus Polish astronomer Birth: February 19, 1473 Death: May 24, 1543 Place of Birth: Torun, Poland

Nicolaus Copernicus

Known for : Proposing a heliocentric (sun-centered) model for the solar system, in which the Sun is stationary at the center, and Earth and the other planets orbit around it. Copernican System theory of planet movements: the theory of Nicolaus Copernicus regarding the mechanics of the solar system, which postulates that the Earth and other planets revolve around the Sun. This theory challenged the Ptolemaic system of astronomy that had prevailed since the 2nd century.

Copernican System

Nicolaus Copernicus Heliocentric plan of the Solar System in the first edition of Copernicus’ De Revolutionibus 1. Sun 2. Mercury 3. Venus 4. Earth 5. Mars 6. Jupiter 7. Saturn 8. Celestial sphere

Nicolaus Copernicus Career: : Studied mathematics at Kraków Academy (now Jagiellonian University) 1496: Went to Italy to study astronomy and law at the University of Bologna 1497: Began observations of the Sun, Moon, and planets 1514?: Wrote Commentariolus, an outline of his astronomical ideas, but did not circulate it widely 1543: Published De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Spheres), which held that Earth and the other planets orbit a centrally located Sun.

First editions of De Revolutionibus

Nicolaus Copernicus Did You Know: Before Copernican theory was accepted, astronomers believed that Earth was stationary at the center of the solar system, and the Sun and planets revolved around it. Copernicus was best known to his contemporaries as a doctor and the Canon of Frauenburg Cathedral. Italian physicist and astronomer Galileo attempted to publicize Copernican theory in the early 1600s, and was convicted of heresy as a result. Copernican theory was not widely accepted until the late 17th century—over 100 years after Copernicus's death. Copernicus's book, De Revolutionibus Orbium Coelestium, was banned as heretical by the Catholic Church until 1835.

Nicolaus Copernicus Planetary Motions According to Copernicus A person moving at uniform speed is not necessarily aware of his motion. Copernicus argued that the apparent annual motion of the Sun about the Earth could be represented equally well by a motion of the Earth about the Sun. The apparent rotation of the celestial sphere could also be accounted for by assuming that the Earth rotates about a fix axis while the celestial sphere is stationary.

Nicolaus Copernicus Planetary Motions According to Copernicus He deduced that the nearer a planet is to the Sun, the greater is its orbital speed. The retrograde motions of the planets were easily understood without the necessity for epicycles. He worked out the correct approximate scale of the Solar System. He resorted to using a number of epicycles in order to achieve the accuracy he required in predicting the positions of the planets in the sky. He maintained the concept of uniform circular motion in his theory.

Nicolaus Copernicus Planetary Motions According to Copernicus The heliocentric model did not prove that the Earth revolves around the Sun. Ptolemaic model was clumsy, it lack the beauty and symmetry of the Copernican model. In the Copernican model the Earth seems to be no longer the central element of the universe.

Nicolaus Copernicus The Scale of the Solar System Definition of Terms 1. Superior Planet Any planet whose orbit is larger than that of the Earth. 2. Inferior Planet A planet closer to the Sun than the Earth is. 3. Elongation The angle formed at the Earth between the Earth- planet direction and the Earth-Sun direction.

Nicolaus Copernicus The Scale of the Solar System Definition of Terms (Continued) 4. Opposition Configuration of the planet when its elongation is 180 degrees. 5. Conjunction The configuration of a planet when it has the same celestial longitude as the Sun, or the configuration when any two celestial bodies have the same celestial longitude or ascension. 6. Quadrature A superior planet is at quadrature when a line from the Earth to the Sun makes a right angle with the line from the Earth to the planet.

Configurations of a superior planet

Configurations of an inferior planet

Nicolaus Copernicus The Scale of the Solar System When an inferior planet is at greatest elongation: EP - must be tangent to the orbit of the planet. - hence perpendicular to the line from the planet to the Sun (PS). We therefore have a right triangle (EPS). Greatest elongation is at PES. ES – will be Earth’s distance from the Sun. PS – distance of the planet to the Sun, can then be found in terms of the Earth’s distance, by geometrical construction or by having trigonometric calculation.

Determination of the distance an inferior planet from the Sun

Nicolaus Copernicus The Scale of the Solar System Suppose planet P is at opposition. We can now time the interval until the planet is next at quadrature. Quadrature happens when: The planet is at P’ and the Earth is at E’. With a knowledge of the revolution periods of the planet and the Earth, we can calculate the fractions of their respective orbits that have been traversed by the two bodies. Thus the angles PSP’ and ESE’ can be determined.

Nicolaus Copernicus The Scale of the Solar System Subtracting PSP’ and ESE’ gives the angle P’SE’. SE’ is the Earth’s distance from the Sun. Enough data are then available to solve the triangle and find the distance for P’S by geometric construction or calculation.

Distances of the Planets

Determination of the distance of the superior planet from the Sun

Nicolaus Copernicus Sidereal and Synodic Period Copernicus recognized the distinction between the sidereal period and the synodic period. Sidereal period is simply the period of revolution of a planet about the Sun. Synodic period is the time required for it to return to the same configuration, such as the time from opposition to opposition or conjunction to conjunction. What is observed directly from the planet is the synodic period.

Relation between Synodic and Sidereal periods of a planet