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The Copernican revolution; “Heliocentrism”

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The Copernican revolution; “Heliocentrism"

What is Heliocentrism???

Heliocentrism is the cosmological model in which the sun is assumed to be at or near the central point, while other bodies (including the Earth) revolve around it. (Britannica, 2019)

Before the heliocentric model is been introduced, most astronomers believed that the universe was Earth-centered. During the 4th century BC, both Plato and Aristotle defended the Geo-centric model. But there were several reasons to believe that the model is not accurate and needed some corrections. For example, it was not possible to explain the changes in the brightness of the planets and their retrograde motions.

Although some astronomers had proposed ideas about a new model, they were not popular among people due to the repercussions of the catholic church. However, Aristarchus of Samos, who was an ancient Greek mathematician and astronomer proposed that the Earth and other planets moved around a definite central object, which he believed to be the sun. (Violatti, 2013)

As European countries emerge from the dark age, they started to trade with Asian countries. This led to a reawakening of interest in Science and Astronomy. This time of re-birth in astronomy was embodied by the work of Copernicus.

Nicolaus Copernicus

Nicolaus Copernicus was born on February 14, 1473, the son of a Polish merchant. His main interests were astronomy and mathematics. He made a great contribution to science, one of them is the development of a new Sun-centered, also known as Heliocentric, model of the solar system.

Nicolaus Copernicus, The Copernican revolution; “Heliocentrism"

Copernicus concluded that the Earth is a planet and all the planets move along circular paths around the sun. Only the moon orbits around the Earth.

Copernicus made new observations and spent more time studying different models of the arrangement of the solar system. But he did not assume (as most astronomers did) that the Earth had to be the center of the universe. He presented a new heliocentric system in an elegant and persuasive way.

Although his ideas were not widely accepted until more than a century after his death, they were discussed among scholars. (contributors, 2020)

Using his concept, he was able to introduce a correct general picture of the solar system. He placed six planets starting nearest the sun, in the correct order: Mercury, Venus, Earth, Mars, Jupiter and Saturn. Further, he deduced that the nearer planet to the sun has the greater orbital speed.

Heliocentric model

Copernicus delayed publishing his work since the Catholic church was defending the Geo-centric model. In 1543, he prepared a synthesis of his work, and published it as “Dē revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres)”.

In this book, he had explained his evidence for the arrangement of the solar system and the positions of planets in the sky could be explained by assuming that Earth and other planets move around the sun. the news of the new heliocentric model spread through the world rapidly.

At that time, people believed in Ptolemy’s Geocentric model. Therefore objections were raised to the heliocentric theory.

If the Earth were moving, Then why we do not feel that motion??

Solid objects will be ripped from the surface, also when a ball dropped from a great height will not strike the ground directly below it. These were some of those objections.

Copernicus argued that the apparent motion of the Sun about Earth during a year, could be represented well by a motion of Earth about the Sun. also he reasoned that the apparent rotation of the celestial sphere could be explained by assuming that the Earth rotates while the celestial sphere is stationary. To the objection that it was implausible for the equator of the Earth to rotate at a thousand miles per hour, Copernicus showed that the Geocentric hypothesis required the celestial sphere to rotate a thousand times faster.

Geocentric vs Heliocentric

The last major objection was the lack of any seasonal change in the angles and brightness of stars.

To understand this phenomenon, first, we have to understand the idea of parallax.

What is meant by Parallax???

Parallax is the shift in the angle that occurs when a nearby object is seen against a distant backdrop from two different perspectives. (Hardegree-Ullman, Impey, & Patikkal, 2012)

In a Geocentric model, stars are assumed to be orbiting around the Earth. Therefore their brightness or angles never change.

But in a Heliocentric model, the Earth is changing its position with respect to other stars, so angles and brightness have to be changed from time to time. That was several hundred years ago before we had the telescope, powerful enough to observe the apparent shift of a star. Hence there was no observation of such an apparent shift.

In defence of the Heliocentric model; they had to hypothesize that the stars were so far away, hence these changes are undetectable.

Parallax shift

Heliocentric model fits with the data which are gained by observations, much better than the Geocentric model.

Copernicus could not prove that Earth revolves around the sun. But he pointed out that the Ptolemaic system was not a successful model.

The Copernican revolution turned the tide of cosmological thought and laid the foundation for modern astronomy.

By Rtr. Nethmi Nawarathna

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