The Discovery of Ganymede

The Discovery of Ganymede
Astronomy is one of the most fascinating sciences. Many people enjoy looking up at the night sky and studying the stars and looking for anomalies such as nebulae, comets, planets, and the like. Citing constellations and watching them track across the sky is one of the pastimes that I personally enjoy.

Now, imagine that you know nothing of the sky. The Earth has been proven to be round, but those stars, the sun – how do they track through the sky? According to Ptolemy in the 2nd century AD, those heavenly bodies rotated around the Earth on an axis that went through the Earth. His idea was accepted by the government and Church and became the dictated theory of planetary motion. This Ptolemaic or geocentric view of the universe lasted for more than 1300 years.

In the 16th century AD, Nicolaus Copernicus challenged Ptolemy’s theory. Through observations and studies, Copernicus proposed that the sun was actually the center of the universe and the Earth revolved around it. He still shared the same Ptolemaic philosophies of the planets as solid bodies that traveled on epicycles, but disagreed with the center-point of the universe. Copernicus died before he ever knew what a stir his heliocentric view of the world would cause.

Johannes Kepler eventually began to use Copernicus’ theory and developed his Laws of Planetary Motion. Those laws coupled with meticulous observation through his own invention – the telescope – Galileo Galilei began to observe the night sky. Unabashedly clinging to Copernicus’ idea that the sun was the center of the universe and basing his observations on Kepler’s laws of planetary motion and cosmological model, Galileo noticed an anomaly in the night sky near Jupiter.

On January 7, 1610, Galileo noted three stationary stars surrounding Jupiter. According to him, they were “invisible because of their smallness,” presumably to the naked eye. He noted they were in a straight line around Jupiter. On January 10, he noted one of these “fixed stars” had disappeared. He hypothesized that the disappearance was due to the star being behind Jupiter. A few days later, it reappeared and he determined these “stars” were orbiting Jupiter. On January 13, he discovered a fourth. Today, we know these to be four of Jupiter’s moons: Io, Europa, Castillo, and Ganymede.

Galileo’s breakthrough discovery, today, would have been praised and lauded as a scientific breakthrough. But, since Copernicus’ ideas were rejected by the Church, Galileo’s work was ridiculed and his loyalty brought into question. In fact, Giordano Bruno, a contemporary of Galileo’s, took Copernicus’ ideas one step further – Copernicus admitted that his heliocentric view of the universe greatly expanded it, but he would not label it infinite. Bruno had no such qualms. He stated the universe was, in fact, infinite and that our solar system was one of many. He suggested there could even be other systems with intelligent life. The Inquisition tried him and burned him at the stake for his theories in 1600.

By 1633, the Church had had enough of Galileo’s theories and heresy. He was tried, as well, and forced to his knees in front of his peers and made to renounce all belief in the theories he held so dear. He was then sentenced to prison for the rest of his life.

Today, Galileo is considered the Father of Modern Science for his advances in astronomy and philosophy. The modern use of his telescope brings us that much closer to furthering his philosophies and exploring the ideas of his contemporary, Bruno. I’ll end with a little bit of humor here. Imagine if had been able to be around during Galileo’s time. I have a feeling he would have had this demotivational hanging on his wall: “Tradition: Just because you’ve always done it that way, doesn’t mean it isn’t incredibly stupid.”

For more information or to view the sources for this article, please visit the following:

Wikipedia Entry
History of Astronomy, abridged
Kepler’s Tradition

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