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Archive for the ‘100s BC’ Category

Hipparchus (190-120 BC) was the greatest astronomer of ancient times. He took astronomy almost as far as it would go before the invention of the telescope.

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”.

A Greek from Nicaea, Hipparchus 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 2000 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 BC 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 in 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 in 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 is lost. Most of what we know of his work comes through Ptolemy.

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The Library of Alexandria was the largest library of ancient times. It stood for centuries, from about 295 BC to 270 AD. 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. But in its time only the Library of Pergamum (the library that invented parchment) could even come close to it.

The Library was conceived as a universal library: to have a copy of every book ever written. It seems it came very close to that for books in Greek.

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 more like a research institute, which brought together some of the greatest minds of the age.

Among other things the Museum and Library gave us:

  • putting things in alphabetical order
  • dividing a work into “books”
  • the Septuagint
  • 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 large the earth is

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

The kings of the Ptolemies who started the Library were like the princes of the Renaissance except that they loved books instead of art.

They say that 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 also sent its men all over the known world to find the oldest copies of books. The older the better.

Because the Library often had many old copies of the same book it could compare the copies that it had and work out what the original must have been. This is how the Library was able to create copies more trustworthy than anyone else’s. What we have of Homer and Aristophanes came from such library copies.

The Library also seems to have had foreign books, in both the original language and translated into Greek. The Septuagint is the famous example: it is the Jewish Scripture as translated by the Library into Greek. When St Paul and others quote Scripture, they almost always quote the Septuagint.

The Library was burned on at least two occasions: first when Julius Caesar fought in Egypt and again in 270 when Aurelian fought Zenobia, queen of Palmyra.

You hear about Christians burning down the Library in 391 but that was the Serapis branch. It was destroyed not as a library but as a temple to idols. Theodosius, who then ruled the empire, had ordered all temples to be turned into Christian churches or shut down.

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