Eratosthenes is a relatively deep lunarimpact crater that lies on the boundary between the Mare Imbrium and Sinus Aestuummare regions. It forms the western terminus of the Montes Apenninus mountain range. The crater has a well-defined circular rim, terraced inner wall, central mountain peaks, an irregular floor, and an outer rampart of ejecta. It lacks a ray system of its own, but is overlain by rays from the prominent crater Copernicus to the south-west.
It is named after ancient Greek astronomer Eratosthenes of Cyrene, who estimated the diameter of the earth, and the distance to the moon and sun.
The Eratosthenian period in the lunar geological timescale is named after this crater, though it does not define the start of this time period. The crater is believed to have been formed about 3.2 billion years ago.
At low Sun-angles, this crater is prominent due to the shadow cast by the rim. When the Sun is directly overhead, however, Eratosthenes visually blends into the surroundings, and it becomes more difficult for an observer to locate it. The rays from Copernicus lie across this area, and their higher albedo serves as a form of camouflage.
He is best known for being the first person to calculate the circumference of the Earth, which he did by applying a measuring system using stadia, which was a standard unit of measure during that time period. His calculation was remarkably accurate. He was also the first to calculate the tilt of the Earth's axis (again with remarkable accuracy). Additionally, he may have accurately calculated the distance from the Earth to the Sun and invented the leap day. He created the first map of the world incorporating parallels and meridians, based on the available geographical knowledge of the era.
Eratosthenes was the founder of scientific chronology; he endeavored to revise the dates of the chief literary and political events from the conquest of Troy. In number theory, he introduced the sieve of Eratosthenes, an efficient method of identifying prime numbers.
Having lost the war to the Spartans, the citizens of Athens elected thirty men as oligarchs. The Thirty instituted oppressive and highly exclusionary laws and instituted a political purge against Athenians who had been Spartan informers and collaborators during the long war. Eventually open hostilities between the Thirty and disenfranchised or disaffected Athenian citizens led to a coup d'etat in 403 BC that deposed them.
He is the subject of a legal oration by the orator Lysias, entitled Against Eratosthenes (Speech 12). According to some critics he is also the subject of another of Lysias' speech, On the Murder of Eratosthenes (Speech 1). However, the age of the Tyrant does not fit with the context of the latter speech: he must have been aged at least 18 in 411 BC to have served as a trierarch, and at least 30 by the time of the Thirty Tyrants period in 403/2 BC. But On the Murder of Eratosthenes suggests that the Eratosthenes referred to in that speech was younger than 30 at the time of his death – he is described as 'neaniskos', a word which Lysias elsewhere uses to refer to younger men.
Craters Theophilus, Cyrillus and Catharina ... Also pictured is 60 kilometre-diameter crater Eratosthenes ... These mountains are essentially what remains of Imbrium’s crater wall ... punctured 60 kilometre-diameter crater called Eratosthenes.
They sweep in a 600-kilometres arc from Promontorium Fresnel in the north to the peaks east of crater Eratosthenes...Crater Eratosthenes ... Crater Eratosthenes (60km)lies in the foothills of south-western Montes Apenninus (Apennines).
The epic result was achieved after dozens of unsuccessful attempts, with users now able to get up close with recognisable craters such as Copernicus, Tycho, Plato, Eratosthenes and Clavius... craters.
