The very slow westward drift of the celestial coordinate system relative to the fixed stars — the *precession of the equinoxes* — was first detected around 130 BC by an astronomer comparing his own star measurements with records from 150 years earlier. Who?
Hipparchus noticed that the stars had shifted about 2 degrees relative to the equinox points since the older Alexandrian observations. He was about 30 percent low on the rate but the discovery itself was the first detection of any systematic motion of the whole celestial sphere — caused, as we now know, by the Earth's axis wobbling like a top on a 26,000-year cycle. Aristarchus had been earlier (3rd century BC) and proposed heliocentrism — also correct, also ignored. Eratosthenes was the librarian. Ptolemy lived three centuries after Hipparchus and preserved most of Hipparchus's work in the *Almagest*.
Read the full story →Hipparchus of Rhodes catalogued a thousand stars, invented trigonometry, discovered the precession of the equinoxes, and may have built the original of the Antikythera mechanism. Almost none of his writing survives.
Related questions
- Around 130 BC, Hipparchus of Rhodes produced the first comprehensive Greek catalogue of stellar positions. Roughly how many stars did he catalogue?
- What major astronomical phenomenon did Hipparchus of Rhodes discover around 130 BC?
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- Robert Koch identified the cholera bacterium in 1883 in Alexandria and confirmed the finding in Calcutta a few months later. But an Italian had identified the same comma-shaped organism nearly 30 years earlier, and been ignored. Who?