Galileo › A game
What did Galileo see?
Eight nights in January 1610, from his own notes. Look at what he looked at, and see if you can work out what he worked out.
In the first days of 1610 Galileo turned a telescope he had made himself on the planet Jupiter. What follows is what he saw, night by night, drawn from the dated entries he printed two months later in The Starry Messenger. At each step you get the same evidence he had, and nothing more.
Jupiter is the large disc. East is on the left, as in his book.
Four circles, seen edge-on
They were not stars, and Jupiter was not passing them. They were going round it, the way the moon goes round us. The pattern changed every night because he was watching four circles from the side, as a man at a table sees a plate as a line.
An illustration, not to scale.
He kept a dated record of every session for two months, and printed it as evidence for anyone who asked: night after night of little diagrams, a circle for the planet and dots for the four. The Starry Messenger came out at Venice in March 1610, about two months after the first night. By the end of that year the Jesuit astronomers in Rome had seen the moons for themselves.
See his pictures of the moon
Positions are from Galileo's own entries in The Starry Messenger (Venice, 1610), in Edward Stafford Carlos's English translation, free at Project Gutenberg. Where he gives distances in minutes of arc they are drawn to scale; where he gives none, the spacing follows his little diagrams roughly. Only the clear nights from 7 to 15 January are shown; he went on until 2 March.
More questions
- Was Galileo tortured?
- Did Galileo really say “and yet it moves”?
- Did the Church refuse to look through Galileo’s telescope?
- Did Galileo prove that the earth moves?
- Why was Galileo put on trial?
- Did Galileo drop weights from the Leaning Tower of Pisa?
- Was Galileo thrown into prison?
- A game: what did Galileo see?
- The timeline, 1564–1992
- The reading room: original sources online
The trial file
A short piece, free: what the documents in Galileo’s own trial file actually say, including the two pages that decided it. It isn’t sold anywhere, and it’s the fastest way to see how these books are built.
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