When the Universe Plants Its Clues

7 January 1610. Three small stars near Jupiter, arranged in a straight line, two to the east and one to the west. I noted them and thought nothing of it — fixed stars near a planet’s path are not unusual. 8 January: they had moved. The two eastern stars were now both to the west. 10 January: only two stars visible, both to the west, the third presumably hidden behind the planet. 13 January: four stars, not three.

Fixed stars do not move like this. Fixed stars do not disappear behind a planet and reappear. What I was looking at was not three fixed stars but four moons, circling Jupiter as the Moon circles Earth — and as Earth, I was now certain, circles the Sun. Not because the moons proved heliocentrism by logic but because they proved by demonstration that there exists in the sky a center of rotation that is not Earth. The universe had been doing this all along, for anyone with an instrument good enough to see it. My telescope was ground to a magnification of thirty; the phenomenon required perhaps eight.

Consilience is not a philosophical position. It is what happens when two sets of data, gathered independently for different purposes, point at the same thing. The phases of Venus, which I had been recording since October, showed a full cycle from crescent to gibbous — geometrically impossible if Venus orbits Earth. The moons of Jupiter showed independent motion around a non-terrestrial center. Neither observation was designed to prove Copernicus. Both did.

The Inquisition will have views on this. I am noting it down anyway.