1. lpetrich says

    Aristotle? From his belief that the terrestrial and celestial realms were very physically different?
    That’s one of the less-appreciated discoveries of modern science. The first hint was when a certain Anaxagoras (about 500 – 430 BCE) concluded from meteorites that the celestial objects were hot glowing rocks. What they have since been discovered to be might be explained to him as “very light naphtha air”. But Plato and Aristotle and various others preferred to believe that the celestial realm follows different physical laws from the terrestrial realm. At first sight, that seems rather plausible. Terrestrial objects like to move linearly toward the Earth’s center, while celestial objects like to move in circles around the Earth’s center. The Moon’s blotches were explained as contamination from the Earth — it is the lowest of all the celestial objects.
    So it went until Galileo started building telescopes and turning them to the sky. The Moon wasn’t just blotchy, it was mountainous, and Galileo estimated the heights of some of the Moon’s mountains. One of his critics argued that the valleys were filled by some invisible substance, but Galileo retorted that there could be mountains of that substance ten times taller than the observed ones, implying that that objection was not even wrong. He looked at Venus, and found that it had phases like the Moon. He looked at Jupiter, and he found some “stars” that traveled around it, like the Moon around the Earth. One critic claimed that they were telescope artifacts, and Galileo offered a large sum of money for a telescope that only makes such artifacts around Jupiter. Another critic claimed that the traditional seven planets correspond to the seven openings of the head, the seven metals, the seven days in the week, and the like, and that there is thus no room for Jupiter’s moons.
    Sir Isaac Newton worked out that the Earth’s surface gravity is the same force that keeps the Moon in orbit, and that Kepler’s three laws were successfully explained by gravity’s inverse-square behavior and his laws of motion. He also tried to calculate the Sun’s larger perturbations of the Moon’s orbit, but with limited success. His successors improved on his calculation methods, going beyond Newton’s lowest-order calculations, and resolving the discrepancies.
    In the 18th cy., a lot of scientists were skeptical about meteorites, calling them stones struck by lightning and other such things. Some scientists around 1800 argued that they were extraterrestrial, but they did not convince many others. But in 1803, there was a meteorite event in the town of L’Aigle, France, and a certain Jean-Baptiste Biot went to investigate. Several people independent of each other had seen the rockfall, and the rocks themselves resembled those other odd rocks, but not any local rocks. So these rocks were extraterrestrial. He made such a strong case that the rest of the scientific community soon came to accept these rocks’ extraterrestrial origin.
    BTW, some UFOlogists consider skepticism about extraterrestrial spaceships much like skepticism about extraterrestrial rocks.
    In the middle of the 19th century, spectroscopy made it possible to find the composition of the Sun, and in the 20th cy., that was extended to the other stars. Cecelia Payne-Gaposchkin discovered that hydrogen and helium, that “very light naphtha air”, were the main constituents of the stars. Working out the structure of stars was also consistent with hydrogen-helium composition and working out their energies was consistent with that also. In fact, we now have a better idea of the interior of the Sun than the interior of the Earth. It’s also possible to work out stellar evolution, and one gets the right distributions of stars in clusters of them. If they all formed at about the same time, then their ages will be very close, and that’s what one finds.
    Back to the Solar System and space exploration, it soon became evident that the solar wind is largely hydrogen and helium, as expected from its composition as worked out by other methods.
    Likewise, Venus, the Moon, Mars, Jupiter, and Titan turned out to be made of familiar elements, as was evident from analysis of bits of them. In 2005, the Japanese spacecraft Hayabusa landed on the asteroid Itokawa and collected samples, which it got back to the Earth in 2010. Now we have Rosetta analyzing 67P’s dust grains and gases, and Philae drilling into that comet. There have been some previous flybys of comets and an impact into one, but no orbiting of comets or soft landings on comets until now.

  2. RJW says

    @1 Ipetrich,

    Aristotle probably would have been a Rosetta landing ‘skeptic’.
    Anaxagoras, Anaxaminder and some of the other pre-Socratics were proto-scientists, what went wrong?
    There’s an interesting book ‘The First Scientist-Anaxaminder’ by theoretical physicist Carlo Rovelli.

  3. lpetrich says

    I see, Ophelia.

    But I don’t think that Aristotle was as horrible as RJW seems to think. He was good at biology, doing lots of dissections. But I concede that the modern understanding of the Solar System would have been more of an adjustment for him than for Anaxagoras.

    The Aristotle-thumpers of academia in the late Middle Ages and early modern times are another story.

Leave a Reply

Your email address will not be published. Required fields are marked *