40 Fun Facts About Aristarchus of Samos

Aristarchus is called the ancient version of which astronomer, who revived his Sun-centred idea in 1543?

Nicolaus Copernicus published the same basic idea some eighteen centuries after Aristarchus, and probably arrived at it independently.

Which Greek mathematician preserved the outline of Aristarchus's lost Sun-centred theory?

Archimedes summarised the theory in a short treatise written for his king, and that summary is the main reason anyone knows Aristarchus proposed it.

A famous Greek treatise estimated how many grains of what would fill the vast universe of Aristarchus?

Sand, at most 10 to the 63rd power grains of it, was the estimate, and the author had to invent a new way of naming huge numbers just to state it.

Aristarchus put the Sun 18 to 20 times farther away than the Moon; what is the true multiple?

About 400 times is the true figure, because the angle he measured as 87° is really close to 89° 50′, far too fine a difference for the instruments of his day.

The lunar crater named after Aristarchus, about 40 km wide, is deeper than which famous chasm?

The Grand Canyon is shallower than this crater, which spans almost 25 miles and sinks more than 2 miles (3.5 km) deep.

Which famous Greek thinker, born around 570 BC, shares his home island with Aristarchus?

Pythagoras was born on Samos roughly 260 years before Aristarchus, and is said to have left the island at about 40 during the rule of the tyrant Polycrates.

To compare the distances of the Sun and Moon, Aristarchus measured an angle at which lunar phase?

At half phase the Moon sits at the corner of a right triangle with Earth and Sun, so one measured angle, which he took as 87°, fixes the ratio of the two distances.

In the model of Aristarchus, what does the Earth do once every day?

The Earth spins on its axis once a day in his model, which explains why the stars seem to wheel overhead; the yearly trip around the Sun is a separate motion.

Aristarchus's figure for the Sun's distance was accepted for some 2,000 years, until which invention?

The telescope finally let astronomers measure the Sun's distance precisely, replacing a value close to his that had been repeated for two millennia.

Aristarchus worked out the Moon's size relative to Earth by studying which kind of event?

A lunar eclipse showed him how wide the Earth's shadow is compared with the Moon, from which he judged the Moon to be roughly a third as wide as the Earth.

Aristarchus built his estimates on the fact that the Sun and Moon share nearly the same what?

Apparent size was his starting point: because the two discs look equal, their true widths must be in the same proportion as their distances from us.

The home island of Aristarchus lies in which sea, about a mile off the coast of modern Turkey?

The Aegean Sea surrounds Samos, which the Mycale Strait, only about a mile wide, separates from the Turkish mainland.

Aristarchus probably studied in which city, where his teacher also tutored the future Ptolemy II?

Alexandria is the likely place, because his teacher spent years in Egypt as tutor to the young prince before returning to Athens to lead a famous school.

The Roman architect Vitruvius credited Aristarchus with a bowl-shaped version of which instrument?

A sundial shaped like a hollow hemisphere, with a pointer in the middle to cast the shadow, is the invention Vitruvius describes, along with a flat disc version.

Besides a lunar crater, which kind of Solar System body carries the name 3999 Aristarchus?

An asteroid in the main belt between Mars and Jupiter carries his name; it was discovered in January 1989 and given the number 3999.

The lunar crater Aristarchus is the brightest large feature on the Moon mainly for which reason?

It is relatively young, so the solar wind has not yet had time to darken the rock that the impact dug up.

The teacher of Aristarchus went on to lead which Athenian school, founded by Aristotle?

The Lyceum made him its third head in about 287 BC, following Aristotle himself and Theophrastus.

According to Ptolemy, Aristarchus observed which annual astronomical event in the year 280 BC?

The summer solstice he timed in 280 BC followed a Greek tradition: Meton had made the same observation at Athens about 150 years earlier, in 432 BC.

The ideas of Aristarchus lost out to the Earth-centred system later set down in which work by Ptolemy?

The Almagest, written in the 2nd century AD, fixed the Earth at the centre so convincingly that its model was inherited by medieval astronomy.

Aristarchus placed the stars immensely far away to explain the absence of which annual shift?

Parallax is real but tiny: the first successful measurements of a star's shift came only in the 1830s, about two thousand years after Aristarchus.

Which Greek writer's work about the face seen in the Moon tells of Aristarchus and an impiety charge?

Plutarch also records that Aristarchus offered his moving Earth only as a hypothesis, while a later follower asserted it as fact.

The crater right beside Aristarchus on the Moon bears the name of which ancient Greek historian?

Herodotus is the lava-flooded neighbour just to the west, darker and slightly smaller than Aristarchus, so the two craters make a striking pair.

Apollo 15 detected signs of which gas seeping from the Moon near the crater Aristarchus?

Radon gave itself away through a rise in alpha particles as the spacecraft passed 110 km overhead in 1971, and a later orbiter confirmed the leak.

The crater Aristarchus stands out even on the Moon's unlit part when it glows faintly with what?

Earthshine, sunlight reflected from our planet onto the Moon's unlit portion, is enough to pick out this crater, whose surface reflects nearly twice as much light as most lunar features.

A later Aristarchus, the most influential ancient scholar of Homer, came from which Greek island?

Samothrace produced the other Aristarchus, who was born about a decade after the astronomer died and rose to run the great royal library in Egypt.

Which is the only work of Aristarchus to survive, though it never mentions his Sun-centred theory?

On the Sizes and Distances of the Sun and Moon keeps the Earth at the centre throughout, which suggests it was written early in his career.

A rule of trigonometry comparing sines and tangents of acute angles is known as Aristarchus's what?

Inequality is the word, and Ptolemy later relied on the same rule while constructing his table of chords.

Which philosopher, born on Samos about thirty years before Aristarchus, founded a school in Athens?

Epicurus was born on Samos to Athenian settlers in 341 BC and later taught in a garden he owned, about halfway between two rival schools.

Which later astronomer reused the geometry of Aristarchus and put the Moon 67 Earth radii away?

Hipparchus followed the same procedure in the 2nd century BC, and Ptolemy later used it again to put the Moon 59 Earth radii away.

Long before Aristarchus, which philosopher taught that the stars are fiery bodies of the same nature as the Sun?

Anaxagoras had pictured both Sun and stars as red-hot masses, with the stars simply too far away for their heat to be felt.

The lunar crater Aristarchus received its name in 1651 from which Italian astronomer?

Giovanni Riccioli did not accept a moving Earth himself, yet he gave craters to its champions, and his 1651 names became the official standard in 1935.

The plateau that holds the crater Aristarchus rises from the middle of which lunar lava plain?

Oceanus Procellarum, the Ocean of Storms, surrounds a tilted block of crust about 200 km across that stands up to 2 km above the lava plain.

Who is the only other ancient astronomer known by name to have backed Aristarchus's Sun-centred model?

Seleucus of Seleucia, who lived about a century after Aristarchus, is said to have held the theory as fact, and also taught that the Moon causes the tides.

Which head of the Stoic school, a Sun worshipper, is linked to an impiety charge involving Aristarchus?

Cleanthes is usually cast as the accuser, but in the surviving manuscripts the names stand the other way round, with Aristarchus calling for the charge.

Before Aristarchus, which Greek philosopher had already set the Earth circling a 'central fire' instead of the Sun?

Philolaus had the Earth, Moon, Sun and planets all circling an unseen fire, one of the first Greek systems to take the Earth out of the centre.

Which philosopher, nicknamed 'the Physicist', is named as the teacher of the young Aristarchus?

Strato sought purely physical explanations for natural phenomena, and before leading his school he served as tutor to a future king of Egypt.

Which British scholar published a 1913 study, Greek text and translation of Aristarchus?

Thomas Heath was a career civil servant and keen mountaineer who also put Euclid and Apollonius into English.

Aristarchus's surviving book was first printed in Greek in 1688 by which Oxford professor of geometry?

John Wallis worked from medieval manuscripts collected by Sir Henry Savile, and is also credited with introducing the symbol for infinity.

A Sun-distance error traceable to Aristarchus was still in use around 1600 in the work of which great observer?

Tycho Brahe kept the ancient figure even though his own observations of the planets and stars were unprecedentedly accurate for their time.

The treatise that preserves the Sun-centred theory of Aristarchus is addressed to which king of Syracuse?

Gelon ruled alongside his father Hiero II and died shortly before him, so he never reigned alone.