How We Came To realise The Sun As The Center Of Our Solar System

The Sun-centered model of the solar system was initially suggested more than a thousand years before Copernicus.

What does our Solar System actually look like? If we were to someway fly ourselves above the plane where the Sun and the planets are, what would we perceive in the center of the Solar System? The response took a while for astrophysicists to figure out, leading to a discussion between what is acknowledged as the geocentric (Earth-centered) model and the heliocentric (Sun-centered model).

The ancients agreed that there were certain bright points that would seem to move amongst the background stars. While who precisely discovered the "naked-eye" planets (the planets you can see without a telescope) is lost in ancient times, we do know that cultures all over the world seen them.

The Solar System. Image Credit: NASA

The ancient Greeks, for example, thought the planets to comprise Mercury, Venus, Mars, Jupiter and Saturn — also the Moon and the Sun. The Earth was in the center of it all (geocentric), with these planets orbiting about it. So significant did this become in culture that the days of the week were entitled after the gods, signified by these seven moving points of light.

Earth is at the center of this model of the universe created by Bartolomeu Velho, a Portuguese cartographer, in 1568. Credit: NASA/Bibliothèque Nationale, Paris.

All the same, not every Greek assumed that the Earth was in the middle. Aristarchus of Samos, according to NASA, was the firstly identified person to say that the Sun was in the center of the cosmos. He suggested this in the third century BCE. The impression never really caught on, and lay latent (as far as we can tell) for some centuries.

Because European researchers trusted on Greek sources for their education, for eras most people followed the lessons of Aristotle and Ptolemy, according to the Galileo Project at Rice University. But there were some things that didn't make logic. For example, Mars sometimes seemed to move backward with respect to the stars before moving onward again. Ptolemy and others clarified this using a system called epicycles, which had the planets moving in little circles within their bigger orbits. [At left: The retrograde motion of Mars. Credit: NASA]

But by the fifteen and sixteenth centuries, astrophysicists in Europe were fronting other problems, the project added. Eclipse tables were becoming imprecise, sailors required to keep track of their location when sailing out of sight of land (which directed to a new method to calculate longitude, based partly on precise timepieces), and the calendar dating from the time of Julius Caesar (44 BCE) no longer was correct in defining the equinox — a difficulty for officials concerned with the timing of religious holidays, chiefly Easter. (The timing difficulty was later solved by rearranging the calendar and instituting more scientifically harsh leap years.)

While two 15th-century astrophysicists (Georg Peurbach and Johannes Regiomontanus) had already referred the Greek texts for scientific errors, the project continued, it was Nicolaus Copernicus who took that knowledge and applied it to astrophysics. His observations would transform our thinking of the world.

Printed in 1543, Copernicus' De Revolutionibus Orbium Coelestium (On the Uprisings of the Heavenly Bodies) summarised the heliocentric universe similar to what we know today. Among his concepts, according to Encyclopedia Britannica, was that the planets' circles should be plotted with respect to the "fixed point" Sun, that the Earth itself is a planet that turns on an axis, and that when the axis alters directions with respect to the stars, this causes the North Pole star to change over time (which is now recognized as the precession of the equinoxes.)

Placing the Sun at the center of our Solar System, other astrophysicists started to understand, simplified the orbits for the planets. And it helped clarify what was so strange about Mars. The cause it backs up in the sky is the Earth has a smaller orbit than Mars. When Earth passes by Mars in its orbit, the planet seems to go backwards. Then when Earth finishes the pass, Mars seems to move ahead again.

Other supports for heliocentrism started to arise as well. Johannes Kepler's rules of motions of the planets (based on work from him and Tycho Brahe) are founded on the heliocentric model. And in Isaac Newton's Principia, the researcher described how the motions happen: a force called gravity, which appears to be "inversely proportional to the square of the distance between objects", according to the University of Wisconsin-Madison.

Newton's gravity theory was later displaced by that of Albert Einstein, who in the early 20th century suggested that gravity is in its place a warping of space-time by massive objects. That said, heliocentric measurment guide spacecraft in their orbits today and the model is the best way to define how the Sun, planets and other objects move.

Solar System


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