Comments on: How Galileo’s Moons Changed The World

By: Brian Koberlein

Brian Koberlein — Sat, 16 Jan 2016 19:29:06 +0000

Yeah, the verification of the heliocentric model was not simply cut and dry. But by the time the “proof” of stellar aberration and parallax came along there was little doubt among the scientific community that the Earth did indeed move around the Sun. True, Galileo’s observations were compatible with Tycho’s model, but Tycho was incompatible with Kepler and Newton. When scientists write history, they revise heavily.

By: Mark Attorri

Mark Attorri — Sat, 16 Jan 2016 14:18:37 +0000

A very interesting and enjoyable post. My only disappointment is that it repeats the common fallacy that Galileo’s observations “gave us proof of a heliocentric universe.” Galileo’s discoveries, particularly his observations of the phases of Venus, certainly disproved the Ptolemaic/Aristotelian model of the universe (according to which all the heavenly bodies orbited the earth). But they were entirely consistent with other geocentric models, such as the one proposed by Tycho Brahe (under which the planets orbited the sun, while the sun and the moon orbited the earth). In fact, the weight of scientific evidence actually favored Tycho’s system over heliocentrism for a period of time even after Galileo died; it wasn’t until later in the 17th century that the gradual accumulation of evidence swung the balance the other way, and actual “proof” came only in the 18th and 19th centuries (with the discovery of the aberration of starlight and detection of stellar parallax). An excellent recent book on all of this is Christopher Graney’s “Setting Aside All Authority: Giovanni Battista Riccioli and the Science against Copernicus in the Age of Galileo.” Anyway, I’m very pleased to have discovered the site and look forward to checking back.

By: Jens Riggelsen

Jens Riggelsen — Thu, 14 Jan 2016 18:01:57 +0000

Soon after Danish astronomer Ole Rømer realized that a delay in the timing of these eclipses when Earth was moving away from Jupiter was due to light having a finite speed (and having to travel an extra distance of one Earth orbit diameter). At the time it was generally thought that light travelled infinitely fast.
Because the speed of light is finite and because the universe is only 13.82 billion years old, we can not possibly see further than 13.82 billion light years away (1 light year being the distance light travels in a year). Everything within that distance from us is what we call the observable universe, though often we forget the “observable” part of the name.
The moons of Jupiter gave us the size of the universe.