Eratosthenes

Now it's time for the Lunar Feature of the Month.

This month, we're going to take a look at the crater Eratosthenes.

Eratosthenes sits near the eastern edge of Mer Imbrium, close to the southern end of the Apennine Mountains.

It is a striking crater, about 58 kilometers across, with sharply defined terrace walls and a prominent group of central peaks.

What makes Eratosthenes such an interesting object is the way its appearance changes with the lighting.

When it's close to the terminator, the low sun angle throws deep shadows across the crater floor and brings out the terracing along the inner walls.

The central peaks can cast long shadows as well, making the crater look much more dramatic than it does when the sun is higher overhead.

Eratosthenes is also geologically important because it gives its name to the Eratosthenian period in lunar history.

Like third century BC.

Oh, sorry, Eratosthenes-

Yeah

... calculated the size of the earth-

They were afraid they were gonna fall off the Earth." Probably not.

So let's just go all the way to the beginning and start with the guy who should have just ended this entire debate forever, and his name was Eratosthenes.

And around 240 BC, he was the chief librarian at the Library of Alexandria.

It's probably the most, like, important collection of knowledge in the ancient world.

Unfortunately, it burned down, but there's a whole other episode on that.

Eratosthenes had heard that there was something strange happening year over year, and it was called the Syene, which is in modern-day Aswan in southern Egypt.

So at noon on the summer solstice, the sun sat almost perfectly overhead, and people could look down into a deep well, and they could see sunlight hitting the bottom.

So a vertical object standing there would basically cast no shadow.

The second life adds, Some say that he returned to Alexandria and again recited his poem with the utmost success, so that he was honored with the libraries of the museum and was buried with Callimachus.

The last sentence may be interpreted by the notice of Sudas, who informs us that Apollonius was a contemporary of Eratosthenes, Euphorion, and Timarchus, in the time of Ptolemy Euergetes, and that he succeeded Eratosthenes in the headship of the Alexandrian library.

Sudas also informs us elsewhere that Aristophanes, at the age of sixty-two, succeeded Apollonius in his office.

Many modern scholars deny the bibliothecariate of Apollonius for chronological reasons, and there is considerable difficulty about it.

The date of Callimachus' hymn to Apollo, which closes with some lines, 105 to 113, that are admittedly an allusion to Apollonius, may be put with much probability at 248 or 247 BC.

Apollonius must, at that date, have been at least twenty years old.

Eratosthenes died 196-193 BC.

This would make Apollonius seventy-two to seventy-five when he succeeded Eratosthenes.

He was puzzled by the Nile floods, which began in the summer, a season when Egypt had no rainfall.

Geographers in Europe, Africa, and Arabia, dating back to Eratosthenes in the 2nd century BCE, speculated that the source was a collection of lakes in central Africa.

Many early maps of Africa showed the Nile originating in large lakes in Africa's interior, but until the 1600s, they were all speculative and not based on firm scientific knowledge.

There is a significant difference in agricultural practices between the northern nations of the Nile Basin, Egypt, Sudan, and South Sudan, and the southern nations, Uganda, Ethiopia, etc.

Besides this, one of Alexander's admirals, named Nearchus, learned to carry his ships from the mouth of the Indus to the Arabian Gulf.

later on a greek sailor hippalus found that by using the monsoons at the appropriate times he could sail direct from arabia to india without laboriously coasting along the shores of persia and beluchistan and in consequence the greeks gave his name to the monsoon for information about india itself the greeks were for a long time dependent upon the account of megisthenes an ambassador sent by seleucus one of alexander's generals to the indian king of the punjab knowledge was thus gained of the east additional information was obtained about the north of europe by the travels of one pythius a native of marseilles who flourished about the time of alexander the great three thirty three b c and he is especially interesting to us as having been the first civilized person who can be identified as having visited britain he seems to have coasted along the bay of biscay to have spent some time in england which he reckoned as forty thousand stadia or four thousand miles in circumference and he appears also to have coasted along belgium and holland as far as the mouth of the elba bithius is however chiefly known in the history of geography as having referred to the island of thule which he described as the most northerly point of the inhabited earth beyond which the sea became thickened and of a jelly-like consistency he does not profess to have visited thule and his account probably refers to the existence of drift-ice near the shetlands All this new information was gathered together and made accessible to the Greek reading world by Eratosthenes, librarian of Alexandria, 240-196 BC, who was practically the founder of scientific geography.

He was the first to attempt any accurate measurement of the size of the earth and of its inhabited portion.

Meet the Red Bull Dragonberry Emergizer.

With his aid, and doubtless that of others, he set himself to study the problem of the possibility of a sea voyage to India around the coast of Africa.

we have seen that Ptolemy, with true scientific caution, had left undefined the extent of Africa to the south.

But Eratosthenes and many of the Roman geographers, even after Ptolemy, were not content with this agnosticism, but boldly assumed that the coast of Africa made a semicircular sweep from the right horn of Africa, just south of the Red Sea, with which they were acquainted, round to the northwestern shore, near what we now term Morocco.

If this were the fact, the voyage by the ocean along this sweep ashore would be even shorter than the voyage through the Mediterranean and Red Seas, while of course there would be no need for disembarking at the isthmus of Suez.

we have seen that Ptolemy, with true scientific caution, had left undefined the extent of Africa to the south.

But Eratosthenes and many of the Roman geographers, even after Ptolemy, were not content with this agnosticism, but boldly assumed that the coast of Africa made a semicircular sweep from the right horn of Africa, just south of the Red Sea with which they were acquainted, round to the northwestern shore near what we now term Morocco.

If this were the fact, the voyage by the ocean along this sweep ashore would be even shorter than the voyage through the Mediterranean and Red Seas, while of course there would be no need for disembarking at the Isthmus of Suez.

The writers who thus curtailed Africa of its true proportions assumed another continent south of it, which, however, was in the torrid zone and completely uninhabitable.

By a curious chance, they happened to be very near the line and with the inaccurate maps of the period a pretty subject of quarrel was afforded between the portuguese and spanish commissioners who met at badajos to determine the question this was left undecided by the junta but by a family compact in fifteen twenty nine charles v ceded to his brother-in-law the king of portugal any rights he might have to the malucas for the sum of three hundred and fifty thousand gold ducats while he himself retained the philippines which have been spanish ever since by this means the indian ocean became for all trade purposes a portuguese lake throughout the sixteenth century as will be seen from the preceding map showing the trading stations of the portuguese all along the shores of the ocean but they only possessed their monopoly for fifty years, for in 1580 the Spanish and Portuguese crowns became united on the head of Philip II, and by the time Portugal recovered its independence in 1640, serious rivals had arisen to compete with her in Spain for the monopoly of the Eastern trade.

End of chapter 6 CHAPTER VII TO THE INDIES WESTWARD, THE SPANISH ROUTE, COLUMBUS AND MAGELLAN While the Portuguese had, with slow persistency, devoted nearly a century to carrying out Prince Henry's idea of reaching the Indies by the eastward route, a bold yet simple idea had seized upon a Genoese sailor, which was intended to achieve the same purpose by sailing westward.

The ancients, as we have seen, had recognized the rotundity of the earth, and Eratosthenes had even recognized the possibility of reaching India by sailing westward.

Certain traditions of the Greeks and the Irish had placed mysterious islands far out to the west in the Atlantic, and that great philosopher Plato had imagined a country named Atlantis far out in the Indian Ocean, where men were provided with all the gifts of nature.