Johannes Kepler Trivia
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49 free Johannes Kepler trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Johannes Kepler was a sickly, half-blind mathematics teacher who inherited Tycho Brahe's Mars observations, fought them for years and emerged with elliptical orbits, the area law and the harmonic law that Newton would later derive from gravity. He also founded modern optics, explained why snowflakes have six sides, wrote what may be the first science-fiction story, and spent six years defending his mother from a witchcraft charge. This quiz covers the astronomy, the mathematics and the turbulent life. Easy questions ask what his three laws describe, which planet's orbit he cracked and who his famous employer was. Harder ones want the town of his birth, the Platonic solids in his first book, the emperor he served, how many failed attempts preceded the ellipse, the year of his third-law epiphany, the war that burned his printing works, the barrel-measuring treatise that helped invent calculus, the conjecture solved only in 2017 and how many planets his namesake telescope confirmed. Every answer was checked against Wikipedia's biography of Johannes Kepler, and each question carries the sentence that supports it. Written for astronomy and physics teachers, students and quiz hosts. Related quizzes: Astronomy, Nicolaus Copernicus and Famous Scientists.
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Q 01Which word did Kepler coin in 1610 for the moons Galileo had found circling Jupiter?
Satellites
Satellites, meaning attendants, was Kepler's word for the four bodies escorting Jupiter. Galileo had named them the Medicean Stars to flatter his patrons, but it was Kepler's term that lasted.
Q 02In which city did Kepler join Tycho Brahe in 1600 and go on to do his greatest work?
Prague
Prague took Kepler in as a religious refugee in 1600, after he refused to change his faith to keep a teaching job. Within two years he had inherited both Tycho's court post and his unrivalled observations.
Q 03Which planet's orbit did Kepler analyse under Tycho's direction, leading to his first two laws?
Mars
Mars exposed the flaw in circular orbits. Kepler's best circular model still missed Tycho's observations by eight minutes of arc, and rather than blame the data he threw the model out and started again.
Q 04What shape did Kepler finally settle on for a planet's path around the Sun?
An ellipse
An ellipse, with the Sun at one focus. Kepler spent years on circles and then on an egg-shaped oval before finding that the true path lay midway between the two.
Q 05Kepler's second law says that a line from the Sun to a planet sweeps out what?
Equal areas in equal times
Equal areas in equal times, which means a planet has to speed up when it is near the Sun and slow down when far away. Kepler found this rule before he knew the true shape of the orbit.
Q 06Kepler's third law links a planet's year to what?
Its distance from the Sun
Its distance from the Sun: the square of the year grows as the cube of the distance. Kepler recorded that the idea came on 8 March 1618, was rejected after a botched calculation, and returned for good on 15 May.
Q 07Kepler's 1619 book, which contains his third law, tried to explain the design of the heavens through what?
Musical harmony
Musical harmony: Kepler believed the planets' changing speeds sounded out notes in a God-given scale. The law for which the book is remembered appears in its last part, as just one more harmony among many.
Q 08In which present-day country was Kepler born in 1571?
Germany
Germany: he was born in Weil der Stadt, then a tiny free city of the Holy Roman Empire near Stuttgart. Religious upheaval kept him moving, and almost all his famous work was done far from home.
Q 09What childhood illness left Kepler with weak vision and crippled hands?
Smallpox
Smallpox in early childhood marked him for life. With eyesight too weak for fine observing, Kepler became the great theorist instead, dependent on other people's measurements.
Q 10Which 1577 celestial event did the young Kepler watch from 'a high place' with his mother?
The Great Comet
The Great Comet of 1577 drew the eyes of astronomers all over Europe that winter. Three years later Kepler was called outdoors to watch a lunar eclipse and remembered the Moon turning quite red.
Q 11What was Kepler's father Heinrich's profession before he abandoned the family?
Mercenary
Mercenary: though a Protestant, Heinrich hired himself out to the Catholic Spanish army fighting Protestant rebels in the Netherlands. He is thought to have died in that war.
Q 12At which university did Kepler study, intending to become a minister?
Tübingen
Tübingen was meant to make a pastor of him. Instead his mathematics professor there, Michael Maestlin, one of the earliest converts to a Sun-centred universe, turned him toward astronomy.
Q 13Which Protestant church barred Kepler from communion in 1612 for refusing to sign its creed in full?
Lutheran
Lutheran, the church he had once trained to serve. Kepler doubted part of its Formula of Concord and would not condemn Calvinists, whom he called brothers in Christ, so he never signed; the ban was never lifted.
Q 21What accusation was made against Kepler's mother Katharina in Leonberg in 1615?
Witchcraft
Witchcraft: a neighbour claimed that a drink from Katharina had made her ill. Kepler ran his mother's defence himself, and she refused to confess even when threatened with torture; she was freed in 1621.
Q 22Kepler worked out the minute of his own conception and concluded he had been born how?
Prematurely
Prematurely: by his own reckoning Kepler was a seven-month baby, conceived on his parents' wedding night. He described his childhood self as weak and sickly.
Q 23What did Kepler spend two years choosing from a shortlist of eleven?
A second wife
Q 14In which Austrian city did Kepler take a job teaching mathematics and astronomy in April 1594, aged 22?
Graz
Graz gave him his first job, at a Protestant school. Six years later a Counter-Reformation commission banished him, along with sixty other men, for refusing to change his faith.
Q 15Kepler's Mysterium Cosmographicum (1596) explained planetary distances by nesting what inside spheres?
The five Platonic solids
The five Platonic solids, nested one inside another, separate exactly six spheres, one for each planet then known, and Kepler took that for God's blueprint. The idea struck him in the middle of teaching a class.
Q 16What had Kepler's bride Barbara Müller already been twice when they married in 1597?
Widowed
Widowed twice by her early twenties, Barbara was a wealthy mill owner's daughter with a small girl of her own. Her father thought a poor schoolteacher beneath her, and the match nearly fell through while Kepler was away.
Q 17Which Holy Roman Emperor made Kepler his imperial mathematician in 1601?
Rudolf II
Rudolf II gave him the post within two days of Tycho Brahe's death. Paying him was another matter: five months passed before the first salary arrived, and Kepler was still chasing arrears when he died.
Q 18What kind of advice did the emperor regularly seek from Kepler as his imperial mathematician?
Astrological
Astrological: the emperor wanted horoscopes and readings of the heavens in times of political trouble. Kepler supplied them while dismissing most of the craft as evil-smelling dung, in which a patient hen might still find a grain of gold.
Q 19What kind of object was the bright new star Kepler observed in October 1604?
A supernova
A supernova, the most recent stellar explosion seen in our own galaxy. Because it never shifted against the background stars, Kepler argued it lay far beyond the planets, in heavens that were supposed never to change.
Q 20Kepler's manuscript Somnium, describing a trip to the Moon, is sometimes called the first work of what?
Science fiction
Science fiction, though the aim was serious. By describing how the sky would look to someone standing on the Moon, Kepler was arguing that a moving Earth is only a matter of where you stand.
A second wife: in one long letter Kepler weighed eleven candidates in turn, then went back to the fifth, Susanna Reuttinger, an orphan his friends thought beneath him. The marriage was far happier than his first.
Q 24Which comet did Kepler track across the sky in 1607?
Halley's Comet
Halley's Comet: Kepler tracked it in 1607 and decided that comets fly in straight lines. Decades later Edmond Halley used those very records to show it was one comet, returning about every 76 years.
Q 25What purchase in 1613 led Kepler to write a book on measuring the volumes of containers?
Wine for his household
Wine for his household arrived in casks, and Kepler watched the merchant gauge each one by poking a rod in diagonally, whatever its shape. Unconvinced, he set about working out the true volumes himself.
Q 26Kepler's 1615 book on the volumes of curved containers was an early step towards which branch of mathematics?
Calculus
Calculus: Kepler found each volume by treating the solid as an infinite number of thin slices and adding them up, long before the method was made rigorous. It was also the first book ever printed in Linz.
Q 27Whose work on logarithms did Kepler adopt to speed up the calculations for his planetary tables?
John Napier
John Napier's logarithms delighted Kepler but came with no account of how they were built. So he derived his own tables from first principles and published them in 1624.
Q 28What destroyed the press that was printing Kepler's planetary tables in 1626?
Fire during the Peasant War siege
Fire during the Peasant War siege: rebels blockaded Linz that summer, and the printer's house and press went up in flames. Kepler's manuscript survived, and he carried it up the Danube to be printed in Ulm instead.
Q 29Which imperial general, newly Duke of Sagan, became Kepler's last patron in 1628?
Wallenstein
Wallenstein set Kepler up with a printing press at Sagan in Silesia. Kepler felt isolated there by an unfamiliar dialect, and in 1630 he set off again to collect money he was owed.
Q 30In which city did Kepler die on 15 November 1630, while travelling to collect money owed him?
Regensburg
His grave in the Protestant cemetery of St Peter was destroyed a few years later in the Thirty Years' War.