50 Fun Facts About Johannes Kepler

Kepler is best known for his laws describing what?

The three laws describe elliptical orbits, equal areas in equal times, and the link between period and distance.

Which Danish astronomer did Kepler assist in Prague, inheriting his observations on his death in 1601?

The two met at Benátky nad Jizerou in February 1600 and fell out within months before reconciling.

Which planet's orbit did Kepler analyse under Tycho's direction, leading to his first two laws?

He never extended the analysis to other planets in Astronomia Nova because he had no calculating assistants.

What shape did Kepler finally hit upon for planetary orbits in 1604, after roughly 40 failed tries?

He had assumed it was too simple a solution for earlier astronomers to have missed.

Kepler's second law, formulated by late 1602, states that planets sweep out what?

He reached it geometrically after first proposing that a planet's speed was inversely proportional to its distance from the Sun.

On what date did Kepler record his epiphany about the third law of planetary motion?

It was first stated in Harmonice Mundi: the squares of the periods are as the cubes of the mean distances.

In which 1619 book, aligning heavenly harmonies with musical ones, did Kepler first state his third law?

He wrote it while grieving his little daughter Katharina, having set the Rudolphine Tables aside.

Kepler was born on 27 December 1571 in which Free Imperial City, now near Stuttgart?

His grandfather had been the city's Lord Mayor, but the family fortune was in decline by his birth.

What childhood illness left Kepler with weak vision and crippled hands?

It limited his ability as an observer, which is partly why Tycho's data mattered so much to him.

Which 1577 celestial event did six-year-old Kepler watch from 'a high place' with his mother?

At nine he was called outdoors to see a lunar eclipse and remembered the Moon "appeared quite red".

What was Kepler's father Heinrich's precarious profession before he abandoned the family?

Though a Protestant, he is thought to have died fighting for the Catholic Spanish army in the Netherlands.

Under which Tübingen professor did Kepler learn the Copernican system?

Maestlin later helped him get Mysterium Cosmographicum past the university senate.

Why was Kepler denied ordination as a Lutheran minister despite wanting the job?

The same doctrinal scruples got him excommunicated by the Lutheran church in Linz in 1619.

In which Austrian city did Kepler take a job teaching mathematics and astronomy in April 1594, aged 22?

There he issued calendars and prognostications that built his reputation as an astrologer.

Kepler's Mysterium Cosmographicum (1596) explained planetary distances by nesting what inside spheres?

Octahedron, icosahedron, dodecahedron, tetrahedron and cube produced six layers for the six known planets.

Who was Barbara Müller, whom Kepler married on 27 April 1597?

Her father Jobst thought the impoverished teacher an unacceptable match until Mysterium was finished.

Which Holy Roman Emperor appointed Kepler imperial mathematician two days after Tycho's death?

The tables he was charged with completing were named the Rudolphine Tables in the emperor's honour.

What was Kepler's primary official duty as imperial mathematician?

He took a dim view of precise prediction but had cast well-received horoscopes since his student days.

What kind of object was the bright new star Kepler observed in October 1604?

Its lack of parallax put it among the fixed stars, undermining Aristotle's doctrine of unchanging heavens.

Kepler's manuscript Somnium, describing a trip to the Moon, is sometimes called the first work of what?

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.

How many explanatory footnotes did Kepler attach to Somnium after his mother's acquittal?

They ran several times longer than the story itself and explained its hidden lunar geography.

What accusation was made against Kepler's mother Katharina in Leonberg in 1615?

She was imprisoned from 1620 to 1621, refused to confess under threat of torture, and was released on 4 October 1621.

What was the profession of Kepler's mother, Katharina Guldenmann?

She was an innkeeper's daughter; the initial accuser claimed a drink from her had caused illness.

How many potential brides did Kepler consider over two years before marrying Susanna Reuttinger in 1613?

He went back to the fifth candidate; the decision process was later formalised as the "marriage problem".

What did Kepler deliberately choose as his second wedding day, 30 October 1613?

He told his friend Bernegger he wanted "the astronomical spirit" in hiding so he could enjoy the festival day.

What 1613 purchase led Kepler to write Nova stereometria doliorum vinariorum on container volumes?

The barrel-measuring treatise was a step towards calculus; Simpson's rule is still called Kepler's barrel rule in German.

What did Kepler have to do to get his barrel book printed in 1615?

It became the first book ever printed in Linz.

Whose 1614 work on logarithms did Kepler adopt to simplify the Rudolphine Tables?

His own tables, published in 1624, could be used directly on whole numbers.

What destroyed Kepler's house and printing works on the outskirts of Linz in 1626?

His manuscript survived and the Rudolphine Tables were finally printed in Ulm in September 1627.

Which imperial general, newly Duke of Sagan, became Kepler's last patron in 1628?

Kepler had once cast his horoscope through an intermediary; in Sagan he felt lonely among unfamiliar dialects.

In which city did Kepler die on 15 November 1630, while travelling to collect money owed him?

His grave in the Protestant cemetery of St Peter was destroyed a few years later in the Thirty Years' War.

Kepler's 1604 book Astronomiae Pars Optica is regarded as the foundation of which field?

It described the inverse-square law of light intensity and pinhole cameras, though the law of refraction is missing.

What did Kepler recognise about the image formed by the eye's lens on the retina?

He suggested the image was later corrected "in the hollows of the brain" by "the activity of the Soul".

What is the two-convex-lens instrument Kepler described in Dioptrice (1611) now called?

It gave higher magnification than Galileo's convex-plus-concave arrangement and underlies modern refractors.

How did Kepler respond in 1610 when Galileo sought his opinion on the newly discovered moons of Jupiter?

He later published his own observations of the moons; Galileo, to his disappointment, never responded to Astronomia Nova.

Kepler's 1611 New Year's pamphlet Strena Seu de Nive Sexangula gave the first description of what?

It also posed the Kepler conjecture on sphere packing, formally solved by Thomas Hales in 2017.

The Kepler conjecture, solved by Thomas Hales in 2017, concerns the most efficient way to do what?

It grew out of Kepler's speculation about the atomic basis of snowflake symmetry and matters for understanding crystals.

Who made the first ever observation of a transit of Mercury in 1631, on the date Kepler predicted?

Kepler had been so unsure of Mercury's parameters that he told observers to look the day before and after as well.

Which Kepler book, published 1617-1621, became the most widely used textbook in its field in 1630-1650?

It contained all three laws and won many converts to ellipse-based astronomy after his death.

Who derived Kepler's laws from a force-based theory of universal gravitation in the 1687 Principia?

The mathematical challenge became known as "solving the Kepler problem".

How did Carl Sagan describe Kepler?

Arthur Koestler made him the outright hero of his 1959 history The Sleepwalkers.

What did a 2010 exhumation of Kepler's old employer rule out, undermining a book's claim that Kepler poisoned him?

The 2004 book Heavenly Intrigue had speculated Kepler murdered his employer.

Which composer wrote the 1957 opera Die Harmonie der Welt about Kepler?

Philip Glass followed with his own opera, Kepler, in 2009, with a libretto in German and Latin.

How many confirmed planets had the Kepler space telescope detected as of June 2023?

It observed more than half a million stars, and many of the planets carry Kepler's name.

In which city were the Rudolphine Tables finally printed, in September 1627?

Kepler had completed the tables in 1623, but the emperor's requirements and Tycho's heirs delayed publication.

Which Lutheran pastor in Linz refused Kepler communion over his views on the Eucharist?

Kepler could not accept the doctrine of ubiquity, and his appeal to the Stuttgart Consistory failed.

How many children did Kepler have with his first wife Barbara, two of whom died in infancy?

Susanna, Friedrich and Ludwig survived infancy; Friedrich died of smallpox aged six in 1611.

In his 1601 astrology treatise, Kepler is thought to have made the first reference to a tide cycle of how many years?

In his notes to Somnium he went on to attribute tides to the Moon's attraction, a force he likened to magnetism.

Where was Kepler buried, in a grave later destroyed during the Thirty Years' War?

He had travelled to Regensburg hoping to collect money owed to him by the Imperial treasury.

Which humanist scholar became Kepler's friend and correspondent for nearly twenty years after meeting in 1612?

Remarkably, the two men never met again in person after that first encounter.