Weighing Up Galileo's Evidence

There were seven models floating around in the early 1600s:

1. Heraclidean. Geo-heliocentric. Mercury and Venus circle the Sun; everything else circles the Earth.

2. Ptolemaic. Geocentric, stationary Earth.

3. Copernican. Heliocentric, pure circles with lots of epicycles.

4. Gilbertian. Geocentric, rotating Earth. (proposed by William Gilbert in De magnete)

5. Tychonic. Geo-heliocentric. Sun and Moon circle the Earth; everything else circles the Sun.

6. Ursine. Tychonic, with rotating Earth.

7. Keplerian. Heliocentric, with elliptical orbits.

See:

* https://tofspot.blogspot.com/2013/08/the-great-ptolemaic-sma...

* ToC: https://tofspot.blogspot.com/2013/10/the-great-ptolemaic-sma...

* PDF: https://faculty.fiu.edu/~blissl/Flynngs.pdf

By the mid-/late-1600s people leaned toward Kepler, mostly because the math was easiest.

With regards to evidence for the Earth's motion, the first inkling was in 1728 with stellar aberration with in γ-Draconis:

* https://en.wikipedia.org/wiki/Aberration_(astronomy)#Discove...

The first for the rotation of the Earth (around an axis) was in 1791 by Guglielmini:

* https://en.wikipedia.org/wiki/Giovanni_Battista_Guglielmini

We finally got parallax in 1806 by Giuseppi Calandrelli in α-Lyrae.

Stellar parallax was considered since at least Aristotle, as he mentions in his On the Heavens (II.14), and since it is not observed then it is reasonable to conclude that there is no motion (it took several thousand years to develop instruments to actually measure it).

Daniel Whitten's "Matters of Faith and Morals Ex Suppositione" is an interesting read.

It is easy to treat Galileo as fighting the obscurantist church of the 15th century, but as the article explains briefly:

> provocatively voiced the pope’s own arguments through an obtuse Aristotelian called Simplicio

... Galileo's ordeal with the inquisition was mostly due to him making fun of the pope (probably not a good idea). The truth is that until Kepler introduced elliptical orbits and variable orbital speeds, the Copernican heliocentric model still needed epicycles and was not much better than the ptolemaic model.

And the church didn't even care _that_ much. Copernicus himself was a priest and, while he himself was wary of publishing it and framed it as a way to do astronomical calculations without any kind of philosophical implication, in the end it circulated without much fuss.

This of course should not diminish his contributions to the scientific method and his other contribution to astronomical observations (mostly the satellites of Jupiter and the rings of Saturn, though his instrument wasn't good enough to recognize them as rings).

I found this series to be a great read on some of the history of Galileo and the status of scientific understanding at the time I believe part of it has made the rounds on hn before: http://tofspot.blogspot.com/2013/10/the-great-ptolemaic-smac...

> Galileo Galilei’s muttered protest symbolises the triumph of scientific rationality over blinkered, obstructive theology. In the face of all the facts – or so runs the mythology – Pope Urban VIII had refused to accept that the earth is in perpetual motion around the sun. He condemned the heretical astronomer to the relatively mild punishment of house arrest,

Weaselly writing! What is claimed as "myth" here? That theology was obstructive? Did the Pope put his thumb on the scales or not? Did the Pope sentence Galileo to house arrest?

> the pope won that round of the battle by sentencing him to nine years of house arrest.

Right.

Feyerabend has an interesting account of this in “Against Method”. One thing I also found very interesting in his telling is the role of the telescope in revolutionizing naval warfare. Galileo in part was motivated, and supported by, a sort of proto-military-industrial complex.

Galileo was thought to be in the wrong not necessarily for scientific views, but for implied theological arguments based on those views.

For example, scientifically and theologically I thought geocentrism was the prevailing view at that time among scientists (God created the earth as a kind of "moral center" of the universe of God's Creation?); today acentrism (universe has no center) seems to be a prevailing scientific view. So by this logic, Galileo was wrong by modern scientific standards, and theologically some still argue for a kind of geocentrism or other such views (such as "galileowaswrong.com" or other such sites) against Galileo's theological views.

Hence Galileo was rightly criticized for lacking religious caution; his rebellious attitude against religion (again, not necessarily for supporting a speculative scientific view) indeed has caused centuries of harm, pitting science against religion, whereas true science can never contradict religious truth.

> the evidence for Riccioli’s system is weighing down the scale-pan, while Galileo’s less substantiated suggestion rises upward

What exactly is the difference between the two theories? It would be interesting to see them both in the context of the time.