Galileo turns a telescope on the sky
Mountains on the Moon, moons around Jupiter, and phases of Venus.
- When
- —
- Duration
- 365 days
- Known to
- ± 1 year
- Era
- Early Modern, Holocene
In 1609 Galileo builds his own telescope and within months publishes observations that damage the Aristotelian cosmos: the Moon is rough and imperfect, Jupiter has four moons so not everything orbits Earth, and Venus shows a full set of phases that the Ptolemaic arrangement cannot produce. He also sees that the Milky Way is made of stars. The evidence is decisive and public, and he writes in Italian rather than Latin.