Four Amazing Astronomical Discoveries from Ancient Greece

Scientists successful ancient Greece made unthinkable astronomical discoveries. Credit: Gary Bembridge/Wikimedia Commons/CC-BY-2.0

Ancient Greek scientists and mathematicians made immoderate of the astir important and astonishing astronomical discoveries centuries ago.

By Gareth Dorrian and Ian Whittaker

“The Histories,” by Herodotus, who lived from 484 BC to 425 BC offers a singular model into the satellite arsenic it was known to the past Greeks successful the mid-fifth period BC.

Almost arsenic absorbing arsenic what these radical knew, however, is what they did not know. This sets the baseline for the stunning advances successful their knowing implicit the adjacent fewer centuries—simply by relying connected what they could observe with their ain eyes.

Herodotus claimed that Africa was surrounded astir wholly by the sea. But however did helium cognize this astir specified a gigantic onshore mass? The historiographer recounts the communicative of Phoenician sailors who were dispatched by King Necho II of Egypt (about 600 BC), to sail astir continental Africa, successful a clockwise fashion, starting successful the Red Sea.

This story, if true, not lone recounts the earliest known circumnavigation of Africa, but besides contains an absorbing penetration into the astronomical cognition of the past world.

The voyage, of course, took respective years. Having rounded the confederate extremity of Africa, and pursuing a westerly course, the sailors observed the prima arsenic being connected their close manus side, supra the bluish horizon.

This reflection simply did not marque consciousness astatine the clip due to the fact that they didn’t yet cognize that the Earth has a spherical signifier and that determination is simply a confederate hemisphere.

The planets orbit the S,un

A fewer centuries later, determination had already been a large woody of advancement successful cosmology. Aristarchus of Samos (310BC to 230BC) argued that the Sun was the “central fire” of the cosmos, and helium adjacent placed each of the then-known planets successful their close bid of region astir it.

This is the earliest-known heliocentric mentation of the star system.

Unfortunately, the archetypal substance successful which helium makes this statement has been mislaid to history, truthful we cannot cognize for definite conscionable however the superb thinker worked it out.

Aristarchus knew the Sun was overmuch bigger than the Earth oregon the Moon, and helium whitethorn person surmised that it should truthful person the cardinal presumption successful the star system.

Nevertheless it is simply a jaw-dropping finding, particularly erstwhile you see that it wasn’t rediscovered until the 16th century, by Nicolaus Copernicus, who adjacent acknowledged Aristarchus during the improvement of his ain work.

One of the top astronomical discoveries from past Greece: the size of the Moon

One of Aristarchus’ books that did past addresses the sizes and distances of the Sun and Moon. In this singular treatise, Aristarchus laid retired the earliest known attempted calculations of the comparative sizes and distances to the Sun and Moon.

It had agelong been observed that the Sun and Moon appeared to beryllium of the aforesaid evident size successful the sky, and that the Sun was further away. They realized this from star eclipses, caused by the Moon passing successful beforehand of the Sun astatine a definite region from Earth.

Also, astatine the instant when the Moon is astatine archetypal oregon 3rd quarter, Aristarchus reasoned that the Sun, Earth, and Moon would signifier a right-angled triangle.

As Pythagoras had determined however the lengths of triangle’s sides were related a mates of centuries earlier, Aristarchus utilized the triangle to estimation that the region to the Sun was betwixt 18 and 20 times the region to the Moon.

He besides estimated that the size of the Moon was astir one-third that of Earth, based connected cautious timing of lunar eclipses.

While his estimated region to the Sun was excessively debased (the existent ratio is 390), connected relationship of the deficiency of telescopic precision disposable astatine the time, the worth for the ratio of the size of the Earth to the Moon is amazingly close (the Moon has a diameter 0.27 times that of Earth).

Today, we cognize the size and region to the satellite accurately by a assortment of means, including precise telescopes, radar observations, and laser reflectors near connected the aboveground by Apollo astronauts.

The Earth’s circumference

Eratosthenes (276BC to 195 BC) was main librarian astatine the Great Library of Alexandria, and a keen experimentalist. Among his galore achievements was the earliest known calculation of the circumference of the Earth.

Pythagoras is mostly regarded arsenic the earliest proponent of a spherical Earth though seemingly not its size. Eratosthenes’ celebrated and yet elemental method relied connected measuring the antithetic lengths of shadows formed by poles stuck vertically into the crushed astatine midday connected the summertime solstice astatine antithetic latitudes.

The Sun is sufficiently acold distant that, wherever its rays get astatine Earth, they are efficaciously parallel, arsenic had antecedently been shown by Aristarchus. So the quality successful the shadows demonstrated however overmuch the Earth’s aboveground curved.

Eratosthenes utilized this to estimation the Earth’s circumference arsenic astir 40,000km. This is wrong a mates of percent of the existent value, arsenic established by modern geodesy (the subject of the Earth’s shape).

Later, different idiosyncratic called Posidonius (135BC to 51BC) utilized a somewhat antithetic method and arrived astatine astir precisely the aforesaid answer. Posidonius lived connected the land of Rhodes for overmuch of his life. There, helium observed the agleam prima Canopus would prevarication precise adjacent to the horizon. However, erstwhile in Alexandria successful Egypt, helium noted Canopus would ascend to immoderate 7.5 degrees supra the horizon.

Given that 7.5 degrees is 1/48th of a circle, helium multiplied the region from Rhodes to Alexandria by 48 and arrived astatine a worth besides of astir 40,000km.

The archetypal astronomical calculator from past Greece

The world’s oldest surviving mechanical calculator is the Antikythera Mechanism. The astonishing instrumentality was discovered successful an past shipwreck disconnected the Greek land of Antikythera successful 1900.

The instrumentality is present fragmented by the transition of time, but erstwhile intact, it would person appeared arsenic a container lodging dozens of finely machined bronze cogwheel wheels.

When manually rotated by a handle, the gears span dials connected the exterior to amusement the phases of the Moon, timing of lunar eclipses, and positions of the 5 planets past known (Mercury, Venus, Mars, Jupiter, and Saturn) astatine antithetic times of the year.

This adjacent accounted for their retrograde motion—an illusionary alteration successful the question of planets done the sky.

We don’t cognize who built it, but it dates to immoderate clip betwixt the 3rd and 1st centuries BC and whitethorn adjacent person been the enactment of Archimedes.

Gearing exertion with the sophistication of the Antikythera mechanics was not seen again for a 1000 years.

Sadly, the immense bulk of these works were mislaid to past and our technological awakening was delayed by millennia.

As a instrumentality for introducing technological measurement, the techniques of Eratosthenes are comparatively casual to execute and necessitate nary peculiar equipment, allowing those conscionable opening their involvement successful subject to recognize by doing, experimenting, and, ultimately, pursuing successful the footsteps of immoderate of the archetypal scientists.

One tin but speculate wherever our civilization would beryllium present if this past subject had continued unabated.

Gareth Dorrian is Post Doctoral Research Fellow successful Space Science, University of Birmingham.

Ian Whittaker is Lecturer successful Physics, Nottingham Trent University. The nonfiction archetypal appeared in The Conversation and is republished nether a Creative Commons license.