Who Discovered Jupiter?

The simple answer to the question “Who discovered Jupiter?” is “No one discovered Jupiter”. Jupiter, you see, is visible without a telescope. The only heavenly bodies that are brighter than Jupiter are the Sun, the Moon, and the planet Venus (in that order). There are no stars brighter than Jupiter. The International Space Station (ISS) is the only manmade object in space that is brighter than Jupiter (and Venus!).

So technically, there was no “discoverer” of Jupiter since it’s right there for all to see. It’s very far away but it’s also huge. It contains 99% of all of the mass in our solar system except for the Sun, of course! No one had to search to find it.

A very similar and important question, however, is “Who first realized that Jupiter was a planet?”. After all, it simply looks like a really bright star to the naked eye. Even ancient people realized that there was something special about five of the “stars” they saw in the sky. They didn’t stay in the same place each night like the other 6,000 or so other stars that can be seen without any visual aids. They moved around the sky in wierd paths of changing directions. In fact, they were called “wandering stars”.

Then in the 16th century, Nicolaus Copernicus came up with an explanation for those weird movements. Up to that time, it was believed that the Earth was the center of the universe and everything else went around it. Copenicus postulated that if the Earth was actually revolving around the Sun and those five wierd “stars” were also rotating around the Sun, that would explain their erratic movements in the sky! But Copernicus didn’t actually call those “stars” planets. By the way, the five “wanderers” that could be seen with the naked eye were Mercury, Venus, Mars, Jupiter, and Saturn.

The fellow who really derserves the credit for determining that Jupiter is a planet was Italian physicist, mathematician, philosopher, and astronomer Galileo Galilei. Now Galileo was one smart guy and is generally given credit as the father of modern science.

Galileo knew from Copernicus’ work that there were five things in the sky that were orbiting the Sun just like Earth. Were they planets just like Earth? Were they stars that orbit our Sun? Galileo would have to see them better than with the naked eye in order to find out.

In 1609 Galileo used something called a telescope which was, at the time, pretty much a novelty item. A parlour trick to amuse the rich. Intellectuals of the day even refused to have anything to do with the first telescopes. You see, they weren’t made by someone from the intellectual crowd, they were made by common craftsmen. At that time, most intellectuals felt that it was impossible for anything developed by a “common man” to be of any use in any intellectual pursuit. Luckily, Galileo and a few others saw the promise of what they could learn with the telescope.

Galileo was immediately amazed when he looked at two of those wandering “stars”. What turned out to be Jupiter had four tinier lights going around it! Kind of like the Moon goes around the Earth? And what turned out to be Venus went through phases just like our Moon! Galileo knew that meant it revolved on its axis just like Earth.

So anyway, nobody discovered Jupiter but Galileo gets the credit for at least confirming that it is a planet.

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