Archive for the ‘100s BC’ Category

Hipparchus (-190 to -120) was the greatest ancient Greek astronomer. He took astronomy almost as far as it would go before the invention of the telescope some 1700 years later.

Ptolemy is more famous but most of his astronomy is warmed-over stuff he got from Hipparchus, whom he called a great “lover of truth”.

Hipparchus was born in Nicaea and lived on the island of Rhodes where he studied the Sun, the Moon and the stars.

Hipparchus was the first to find out how far away the Moon is. In order to work out the answer, he came up with a new field of mathematics: trigonometry.

Hipparchus made the best star map of ancient times, with some 2,000 stars.

  • It was so good that his practice of using latitude and longitude has been used to map the heavens and the earth ever since.
  • It was so good that it had Uranus on it, a planet that was not discovered till 1900 years later.
  • It was so good that he discovered the precession of the equinoxes: that the sun does not appear in quite the same position on the first day of spring every year. Instead it moves backwards against the background of the stars, going all the way round in 26,700 years.

He started his map in -134 after seeing a new star in the constellation of Scorpio. He thought it was new, but could not be sure. He checked the star maps of Eudoxus and Erastosthenes. They did not have the star, but then he saw how bad their maps were. So he made his own.

The Greeks thought the heavens were perfect and unchanging, so finding a new star was a serious matter.

Hipparchus was the first to measure stars by their brightness. The 20 brightest stars he called first magnitude stars, the next brightest stars he called second magnitude and so on.

Most of what you see in Ptolemy comes from Hipparchus. Those circles within circles (the epicycles) and even most of the numbers. Hipparchus put the Earth at the centre because that is what the best science of the day said: Aristotle’s.

The Earth-centred model of Hipparchus was so good at working out where planets would be on any given day that few doubted it.

His model was just that: a model. But it worked so well that most mistook it for the truth.

Hipparchus and many others knew that Aristarchus had put the Sun at the centre, but it went against common sense (the Earth does not seem to be moving), the best science (Aristotle) and, besides, no one had worked it up into a model as good as that of Hipparchus. Not Aristarchus, not even Copernicus himself over 1600 years later.

Hipparchus was not overthrown till the 1600s when Aristotle was overthrown by Newton. And not until Kepler made some changes to the model of Copernicus.

All but one of his books are lost. Most of what we know of his work comes through Ptolemy.

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The Library of Alexandria (-295 to +646) was the largest library of ancient times. It stood for almost a thousand years. In 2002 a new Library of Alexandria was opened.

The ancient library had about 490,000 scrolls. That comes to about 100,000 of our books or, on a computer, 64 gigabytes. For us that would be a small-city library. In its time only the Library of Pergamum (the library that invented parchment) came close. In our time, the Library of Congress, now the largest, did not pass that size till the late 1800s.

The Library was conceived as a universal library: to have a copy of every book ever written. At 490,000 scrolls it probably came close that for Greek books.

It was not a free-standing, public library. It was part of the Museum of Alexandria, which in turn was part of the king’s estate. It was not a museum as we think of it but something like a research institute, which brought together some of the greatest minds of the age. It had labs, an observatory, a botanical garden and a zoo with a polar bear.

The Museum and Library gave us, among other things:

  • putting things in alphabetical order,
  • dividing a work into “books” (= separate scrolls),
  • the Septuagint (the Greek Old Testament),
  • the works of Homer as we know them,
  • grammar books in the form we are used to seeing them,
  • punctuation,
  • the first good measurement of how big the earth is,
  • latitude and longitude,
  • heliocentrism.

The Library had a branch in the temple of Serapis. It was about a tenth the size but seems to have been opened to the public.

Ships that came to Alexandria were searched for books. Those that were found were copied: the owner got the copy, the Library kept the original! The Library sent buyers abroad to find the oldest copies of books. The older the better. If it had several old copies of the same book, it would work out what the original must have been. That is how the Library came to have the most trustworthy copies in the world.

It had the stolen originals of the plays of Aeschylus, Sophocles and Euripides and books from the libraries of Aristotle and Theophrastus..

Languages: it had books in at least Greek, Egyptian, Aramaic (Babylonian) and Hebrew..

The Library was (partly) destroyed in:

  • -48 under Julius Caesar, who may have taken some of its books to Rome;
  • 272 under Aurelian to put down an uprising in Alexandria;
  • 295 under Diocletian to put down yet another uprising;
  • 391 under Theodosius when the Serapis branch was destroyed as a temple to idols;
  • 646 when Arabs destroyed what remained.

Of its books, 99% are lost forever. But if it were not for the Library, we would not have much of what do have, through copying and recopying, like the works of Aeschylus, Aristophanes, Thucydides and Herodotus.

Of the physical remains of the actual books that once sat in the Library, all we have are some torn pages.

– Abagond, 2006, 2015.

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