Questions to ask Galileo

Galileo's life in eight dates

How to use the questions

Choose questions from at least three groups so your interview covers his science, his conflict with the Church and his private life. A good answer to any of them names a book or a letter, so the notes under each group tell you which document to check. For a wax museum, the telescope questions work best: visitors can picture what he saw.

You can rehearse the interview by voice with an AI Galileo on Yuga, which answers from his writings and the historical record. Treat it as practice. It is an AI recreation, it can be wrong, and your project should cite Galileo's own texts.

Questions about the telescope and what he saw

Record: Galileo did not invent the telescope. A Dutch spectacle maker applied for a patent in 1608, and Galileo built improved versions in 1609, reaching about 20 times magnification. In Sidereus Nuncius (1610) he described mountains and valleys on the Moon, many more stars than the eye can see, and four moons of Jupiter, first seen in January 1610, which he named the Medicean stars after his future patrons. Later that year he observed the phases of Venus.

1. How did you hear about the telescope, and how did you make yours better?
2. What did you see on the Moon that surprised you?
3. How did you work out that the four points of light near Jupiter were moons?
4. Why did you name Jupiter's moons after the Medici family?
5. Why did the phases of Venus matter so much in the argument about the Earth's motion?
6. What did you make of the spots on the Sun?

Questions about motion and mathematics

Record: in The Assayer (1623) he wrote that the book of nature is written in the language of mathematics. In Two New Sciences (1638) he set out that, without air resistance, heavy and light bodies fall at the same rate, and that the distance fallen grows with the square of the time. He tested this by rolling balls down inclined planes. The Leaning Tower experiment comes from his first biographer, Vincenzo Viviani, and is not described in Galileo's own works, so historians doubt it happened as told.

1. Why did you roll balls down slopes instead of dropping them?
2. Did you really drop weights from the Leaning Tower of Pisa?
3. Why do you say nature is written in the language of mathematics?
4. If the Earth moves, why don't we feel it?

Questions about the Church, the Bible and the trial

Record: in his Letter to the Grand Duchess Christina (1615) he argued that the Bible speaks in ordinary language to reach ordinary people and should not be used to settle questions that can be decided by observation and proof. In 1616 he was warned not to defend the moving Earth. The Dialogue of 1632 put the Pope's favourite argument in the mouth of a character called Simplicio, which helped turn Urban VIII, once a friend, against him. He was tried in Rome in 1633 and abjured. Avoid a simple “science against religion” story: Galileo was a Catholic all his life, and many churchmen were themselves astronomers.

1. You were a Catholic. How did you fit your faith together with a moving Earth?
2. What did Cardinal Bellarmine tell you in 1616?
3. Why did you write the Dialogue as a conversation between three characters?
4. Did you mean to mock the Pope through Simplicio?
5. Were you afraid during your trial, and why did you agree to abjure?
6. Did you say “and yet it moves” after the trial?

On the last question: the phrase “Eppur si muove” is not in the trial records and first appears in print in 1757, more than a century later. See did Galileo say and yet it moves.

Questions about house arrest and his family

Record: Galileo never married but had three children with Marina Gamba. His elder daughter, Virginia, became Sister Maria Celeste in a convent at Arcetri. More than 120 of her letters to him survive; his replies are lost. She died in 1634, the year after the trial. Under house arrest he finished Two New Sciences, smuggled out and printed in Leiden in 1638, and went blind.

1. What did your daughter's letters mean to you during the trial?
2. Why did you put your daughters in a convent so young?
3. How did you get Two New Sciences published when your books were banned?
4. What was it like to lose your sight after a life of looking through telescopes?
5. Who visited you at Arcetri?
6. Which of your discoveries do you think will last longest?
7. What would you tell a young mathematician who wants to study the sky?

Sample answers in Galileo's words

Q: Why were people against you before the trial?

Q: Can human beings understand everything nature does?

Q: How were you in your last years?

Q: How should we read the Bible and nature together? His answer, paraphrased from the Letter to Christina (1615): the Bible was written to reach ordinary people and should not be used to decide questions of natural philosophy that the senses and demonstrations can settle.

Questions Galileo could not answer

• Anything about Isaac Newton's law of gravity. Newton was born in the year Galileo died and published in 1687.
• The 1992 statement by Pope John Paul II acknowledging that the Church's judges had erred. That came 350 years after his death.
• The Galileo spacecraft that orbited Jupiter from 1995, or photographs of his moons.
• Why planets move in ellipses: Johannes Kepler published that in 1609 and wrote to Galileo, but Galileo never accepted elliptical orbits. You can ask him why not.

Where to read Galileo's own words

Stillman Drake's Discoveries and Opinions of Galileo (1957) collects The Starry Messenger, the Letter to the Grand Duchess Christina, and parts of The Assayer in readable English. The Dialogue and Two New Sciences are both in print in full translation. Dava Sobel's Galileo's Daughter (1999) translates many of Maria Celeste's letters. The Museo Galileo in Florence shows two of his surviving telescopes and a cracked lens believed to come from the telescope he used to find Jupiter’s moons, and its website has a digital library of his works in Italian.

For the bigger picture, read Copernicus, Kepler and Galileo compared or Newton vs Galileo.