1 post tagged “venus”
Jupiter is shining bright tonight, and with good cause. Three hundred and ninety-nine years ago today, Galileo Galilei changed the world, the nature of science, and the meaning of religion thanks to Jupiter. Using an improved telescope that he had invented, Galileo looked at Jupiter and saw that it had three companions; by the end of the week, he had found a fourth and proven that these small starry messengers revolved around Jupiter. Being a savvy sort, he published his findings in Sidereus Nuncius, a short treatise that was dedicated to Cosimo II de' Medici and called the four moons of Jupiter “Medicean stars”. We now know them as Europa, Ganymede, Callisto, and Io [1] and call them the Galilean satellites.
His discovery was first used as a method for keeping time [2], but it had even deeper implications. Under Aristotle’s view of the cosmos, the Earth was the center and everything revolved around it. Things in the heavens were perfect and pure, and were in heaven because they were pure and perfect. Because the ideology fit so well with the dogma of the Catholic Church, it was adopted as Church Law – to challenge it was to challenge the very essence of belief [3]. Though some troubling differences had arisen between the pure circles demanded by Aristotle and the observed paths of the planets, these were smoothed over by Ptolemy’s “epicycles” of circles on circles. Questioning these ideas was dangerous at best and heresy at worst [4, 5].
Galileo did worse than question them: he made it possible for anyone to see that he was right and the Church was wrong [6]. By simply looking through the telescope, people could see these new moons of another planet. They could see the “jug-ears” of Saturn [7]. They could see the phases of Venus [8]. They could see the spots on the face of the Sun and the scars on the face of the Moon [9]. And they could see that the Milky Way was neither food of the gods nor a nebula but thousands upon thousands of stars like our, scattered across the sky.
Galileo was first rewarded for his discoveries and then punished for his hubris. He became a superstar in Pisa, and other city-states wooed him, trying to get him to move and to bring his beautiful ideas with him. But his ego led him to clash with others, making enemies out of supporters. Eventually, he was brought before the Inquisition for heresy and threatened with torture. He renounced his views and spent the rest of his life under house arrest [10]. It would be 206 years before the Roman Catholic Church would take his works off of the banned list and 376 years before the Vatican would formally clear him of any wrongdoing.
In opening the heavens to us, Galileo laid the foundations of modern science. He showed that clear logic alone (Aristotle’s approach) is not enough. Logic must be backed with evidence and hypotheses must be checked against observations. He also started us on the road to discover who else is out there.
John
[1] Named after the lovers of Jove (Jupiter). Remember that every planet has a system for naming its moons:
In addition, each planet and other body has a unique system for naming its features (e.g., great lovers for features on Eros). Names for newly discovered moons, planets, and features must be approved by the IAU to become “official”.
- Mars the dogs of war Phobos (Fear) and Deimos (Panic)
- Saturn Titans
- Uranus Characters from a Midsummers’ Nights Dream and the Rape of the Lock
- Neptune Nymphs and children of the sea god
- Pluto Workers in Hades
[2] Why is time so important? Because it tells you where you are! From the angle that the sun makes with the horizon at noon, you can tell your latitude (how far north or south you are). But you need to know the time in order to determine your longitude; this is why locations are given in minutes and seconds. If you know the time to within one hour, you can determine your location to within 1700 km. If you know the time to within 1 minute, you can determine your location to within 27.8 km. If you know it to within one second, then you can determine your location with an error of less than 0.5 km. Until the creation of the first accurate, sea-worthy chronometer [a], the stars were the only way to determine time at sea. Using the Medicean stars, Pisan sailors were able to navigate more easily and more quickly across the oceans; it was this that made Pisa a naval power to rival England in the 1600’s. 300 years later, Lewis and Clark used the same method as they tracked across North America. And all of this came from “pure” research!
[3] Or so the Church scholars would have you believe.
[4] Copernicus published his heliocentric theory on his deathbed, and was still reviled in sermons sixty years later. Giordano Bruno held to a heliocentric universe and was burned at the stake for it (and other heresies).
[5] The Roman Catholic Church wasn’t the only group that wanted a geocentric universe. Nearly 1800 years earlier, Aristarchus had been threatened with expulsion from Samos for impeity because he had suggested that it was silly for a huge Sun to orbit a tiny Earth and wanted to have it be the other way around.
[6] While doing so, he also implied that the Pope was an imbecile. Many scholars believe that it was this, rather than his embrace of Copernican theory, that led to his troubles. Note to self: Don’t piss off the absolute ruler of the nation you live in when proposing a radical change to that nation’s beliefs…
[7] Or at least, most of the time, they could see them. This was one of the things that caused Galileo trouble – the rings are tilted and so change their apparent shape and width as Saturn moves in its orbit. When Galileo first saw them, Saturn was directly behind the Earth, so the rings stood out like the brim on a sombrero worn by a man standing behind you. When Galileo was trying to gather support, Saturn had moved in its orbit so the rings were nearly edge on (imagine that man and his sombrero moving over to your right – notice how the brim appears to get smaller?) and very difficult to see. As is the case with modern net trolls, Galileo’s enemies used this one change to argue that everything he did was a lie.
[8] Under the geocentric model, only the new and crescent phases were possible as Venus had to orbit between the Sun and the Earth. In the heliocentric model, all of the phases could be seen (and were).
[9] Not only did these allow Galileo to check Aristarchus’ estimate for the size of the Moon by comparing its mountains to those on Earth, it went directly against the belief that the Moon and Sun were perfect and pure bodies. The sunspots also allowed Galileo to measure the Sun’s rotation (another impossibility, according to Aristotle).
[10] Legends to the contrary, he is unlikely to ever have said “eppure si muove” (“And yet it moves”). To do so would have been foolhardy and needlessly brave – and Galileo was neither.
[a] Detailed in Sobel’s magnificent Longitude. England and France were locked in a battle to develop a way to determine time at sea (with Brussels a distant third); as a result, each had their own Prime Meridian. Britannia ruled the oceans because it was able to solve the problem before France.
[b] Galileo's finger, saved as a reliquary. Shown as requested by MadTante.
