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50 free Johannes Kepler trivia questions with answers — science & nature quiz, new questions added Aug 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 01Kepler is best known for his laws describing what?
Planetary motion
The three laws describe elliptical orbits, equal areas in equal times, and the link between period and distance.
Q 02Which Danish astronomer did Kepler assist in Prague, inheriting his observations on his death in 1601?
Tycho Brahe
The two met at Benátky nad Jizerou in February 1600 and fell out within months before reconciling.
Q 03Which planet's orbit did Kepler analyse under Tycho's direction, leading to his first two laws?
Mars
He never extended the analysis to other planets in Astronomia Nova because he had no calculating assistants.
Q 04What shape did Kepler finally hit upon for planetary orbits in 1604, after roughly 40 failed tries?
An ellipse
He had assumed it was too simple a solution for earlier astronomers to have missed.
Q 05Kepler's second law, formulated by late 1602, states that planets sweep out what?
Equal areas in equal times
He reached it geometrically after first proposing that a planet's speed was inversely proportional to its distance from the Sun.
Q 06On what date did Kepler record his epiphany about the third law of planetary motion?
8 March 1618
It was first stated in Harmonice Mundi: the squares of the periods are as the cubes of the mean distances.
Q 07In which 1619 book, aligning heavenly harmonies with musical ones, did Kepler first state his third law?
Harmonice Mundi
He wrote it while grieving his little daughter Katharina, having set the Rudolphine Tables aside.
Q 08Kepler was born on 27 December 1571 in which Free Imperial City, now near Stuttgart?
Weil der Stadt
His grandfather had been the city's Lord Mayor, but the family fortune was in decline by his birth.
Q 09What childhood illness left Kepler with weak vision and crippled hands?
Smallpox
It limited his ability as an observer, which is partly why Tycho's data mattered so much to him.
Q 10Which 1577 celestial event did six-year-old Kepler watch from 'a high place' with his mother?
The Great Comet
At nine he was called outdoors to see a lunar eclipse and remembered the Moon "appeared quite red".
Q 11What was Kepler's father Heinrich's precarious profession before he abandoned the family?
Mercenary
Though a Protestant, he is thought to have died fighting for the Catholic Spanish army in the Netherlands.
Q 12Under which Tübingen professor did Kepler learn the Copernican system?
Michael Maestlin
Maestlin later helped him get Mysterium Cosmographicum past the university senate.
Q 13Why was Kepler denied ordination as a Lutheran minister despite wanting the job?
His beliefs conflicted with the Formula of Concord
Q 21How many explanatory footnotes did Kepler attach to Somnium after his mother's acquittal?
223
They ran several times longer than the story itself and explained its hidden lunar geography.
Q 22What accusation was made against Kepler's mother Katharina in Leonberg in 1615?
Witchcraft
She was imprisoned from 1620 to 1621, refused to confess under threat of torture, and was released on 4 October 1621.
Q 23What was the profession of Kepler's mother, Katharina Guldenmann?
Healer and herbalist
She was an innkeeper's daughter; the initial accuser claimed a drink from her had caused illness.
The same doctrinal scruples got him excommunicated by the Lutheran church in Linz in 1619.
Q 14In which Austrian city did Kepler take a job teaching mathematics and astronomy in April 1594, aged 22?
Graz
There he issued calendars and prognostications that built his reputation as an astrologer.
Q 15Kepler's Mysterium Cosmographicum (1596) explained planetary distances by nesting what inside spheres?
The five Platonic solids
Octahedron, icosahedron, dodecahedron, tetrahedron and cube produced six layers for the six known planets.
Q 16Who was Barbara Müller, whom Kepler married on 27 April 1597?
A twice-widowed heiress with a young daughter
Her father Jobst thought the impoverished teacher an unacceptable match until Mysterium was finished.
Q 17Which Holy Roman Emperor appointed Kepler imperial mathematician two days after Tycho's death?
Rudolf II
The tables he was charged with completing were named the Rudolphine Tables in the emperor's honour.
Q 18What was Kepler's primary official duty as imperial mathematician?
Providing astrological advice to the emperor
He took a dim view of precise prediction but had cast well-received horoscopes since his student days.
Q 19What kind of object was the bright new star Kepler observed in October 1604?
A supernova
Its lack of parallax put it among the fixed stars, undermining Aristotle's doctrine of unchanging heavens.
Q 20Kepler's manuscript Somnium, describing a trip to the Moon, is sometimes called the first work of what?
Science fiction
A distorted version of the story, in which the narrator's mother consults a demon, may have helped trigger the witchcraft charge against his own mother.
Q 24How many potential brides did Kepler consider over two years before marrying Susanna Reuttinger in 1613?
11
He went back to the fifth candidate; the decision process was later formalised as the "marriage problem".
Q 25What did Kepler deliberately choose as his second wedding day, 30 October 1613?
The day of a lunar eclipse
He told his friend Bernegger he wanted "the astronomical spirit" in hiding so he could enjoy the festival day.
Q 26What 1613 purchase led Kepler to write Nova stereometria doliorum vinariorum on container volumes?
Wine for his household
The barrel-measuring treatise was a step towards calculus; Simpson's rule is still called Kepler's barrel rule in German.
Q 27What did Kepler have to do to get his barrel book printed in 1615?
Bring a printer from Erfurt to Linz at his own expense
It became the first book ever printed in Linz.
Q 28Whose 1614 work on logarithms did Kepler adopt to simplify the Rudolphine Tables?
John Napier
His own tables, published in 1624, could be used directly on whole numbers.
Q 29What destroyed Kepler's house and printing works on the outskirts of Linz in 1626?
Fire during the Peasant War siege
His manuscript survived and the Rudolphine Tables were finally printed in Ulm in September 1627.
Q 30Which imperial general, newly Duke of Sagan, became Kepler's last patron in 1628?
Wallenstein
Kepler had once cast his horoscope through an intermediary; in Sagan he felt lonely among unfamiliar dialects.