For the first time, objects had been observed orbiting another planet, thus weakening the hold of the Ptolemaic model. Venus was observed to go through a sequence of phases similar to the Moon. This could not be explained in the Ptolemaic model but could be accounted for by either the Sun-centered Copernican model or the Earth-centered Tychonic model that had the other planets orbiting the Sun as it orbited the Earth.
Galileo rejected Tycho's model as an unnecessary hybrid and used the discovery to consolidate his support of the Copernican model. Along with contemporaries such as Thomas Harriot, David Frabicius and Christoph Scheiner, Galileo observed dark regions that appeared to move across the surface of the Sun.
Debate centered on whether these were satellites of the Sun or actual spots on its surface. Galileo, in his Letters on Sunspots supported the sunspot interpretation and used it to show that the Sun was rotating. Its blemishes and imperfections again undermined the Aristotelian ideal of a perfect cosmos.
Galileo noted two appendages from the sides of Saturn. These disappeared then later reappeared. It was not until that the Dutch scientist, Christiaan Huygens correctly described them as rings. Even through a telescope the stars still appeared as points of light. Galileo suggested that this was due to their immense distance from Earth. This then eased the problem posed by the failure of astronomers to detect stellar parallax that was a consequence of Copernicus' model.
When on January 8th, led by some fatality, I turned again to look at the same part of the heavens, I found a very different state of things, for there were three little stars all west of Jupiter, and nearer together than on the previous night. These observations also established that there are not only three, but four, erratic sidereal bodies performing their revolutions around Jupiter.
Galileo may also have made the first recorded studies of the planet Neptune, though he didn't recognize it as a planet. While observing Jupiter's moons in and , he recorded a nearby star whose position is not found in any modern catalogues. In Galileo's lifetime, all celestial bodies were thought to orbit the Earth. Supported by the Catholic Church, teaching opposite of this system was declared heresy in Galileo, however, did not agree. His research — including his observations of the phases of Venus and the fact that Jupiter boasted moons that didn't orbit Earth — supported the Copernican system, which correctly stated that the Earth and other planets circle the sun.
In , he was summoned to Rome and warned not to teach or write about this controversial theory. But in , believing that he could write on the subject if he treated it as a mathematical proposition, he published work on the Copernican system.
The planet Venus showed changing crescent phases like those of the Moon, but their geometry could only be explained if Venus was moving around the Sun rather than the Earth.
This undermined the idea that everything in the heavens revolved around the Earth although it was consistent with the Tychonic system as well as the Copernican one. The planet Jupiter was accompanied by four tiny satellites which moved around it. Again, this showed that not everything in the heavens revolved around the Earth. Galileo saw that the Milky Way was not just a band of misty light, it was made up of thousands of individual stars.
This design, however, went unbuilt until after the construction of the first working pendulum clock by Christiaan Huygens. Explore space from the comfort of home. Introducing Illuminates, our accessible guides on space written by Royal Observatory astronomers. Replica of a handheld Galilean telescope. If Galileo were around today, he would surely be amazed at NASA's exploration of our solar system and beyond. After learning of the newly invented "spyglass," a device that made far objects appear closer, Galileo soon figured out how it worked and built his own, improved version.
In , using this early version of the telescope, Galileo became the first person to record observations of the sky made with the help of a telescope. He soon made his first astronomical discovery. At the time, most scientists believed that the Moon was a smooth sphere, but Galileo discovered that the Moon has mountains, pits, and other features, just like the Earth.
When Galileo pointed his telescope at Jupiter, the largest planet in our solar system, he made a startling discovery. The planet had four "stars" surrounding it.
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