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The Early Greek Astronomers
by Kevin Brown : last updated: June 9, 2007

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Observation of the Sun, Moon and Stars, was undoubtedly extremely important in prehistoric time. We know this from ancient drawings, detailed artifacts and the celestially-influenced design of structures such as the pyramids in Egypt and early stone circles like Stonehenge in England.

However, as far as we can tell, the ancient observers did not approach their astronomy in a way we would recognise today, as a modern scientific method, based on theories, experiments, recorded observations, written-up results and published conclusions.

The big change in astronomy which turned it into the modern science we recognise today, first started around 300BC with the early Greek astronomers.

Aristotle

The first of these early Greek astronomers was Aristotle. He was a philosopher and scientist who was taught by the great Plato and worked around 330BC.

Aristotle came up with a model for the Universe.

Unbelievably, his model of the Universe was to dominate astronomical thinking for almost the next 2000 years.

Quite a claim to fame!

He said that the Earth was at the centre of the Universe and all other bodies, the Sun, Moon and stars, were arranged on a number of concentric crystalline spheres.

He also developed the first “periodic table” of elements. There were just four elements – earth, water, air and fire.

Aristarchus

There were two men called Aristarchus in Greece, who both appear in the history of astronomy. The important one for our story here was Aristarchus of Samos and he worked a few decades after Aristotle.

Aristarchus seriously challenged the ideas of Aristotle by saying that the Sun, not the Earth, was at the centre of all things. He also said that the stars must be much further away than the Sun and Moon, because they did not show the same relative motion.

These ideas were of course, bang on. Nearly 2000 years later, the same fundamental idea that the Earth was not the centre of all things would get the famous astronomer Gallileo into a LOT OF TROUBLE with the 17th century establishment.

But the work of Aristachus, which also covered some other excellent theories more than 200 years BC, was ignored as far as we can tell.

Hipparchus

Hipparchus worked at Rhodes and is considered to be the greatest astronomer of ancient Greece.

He compiled a catalogue of over 800 fixed stars. He also worked out the distance from the Earth to the Moon.

But his most astonishing achievement was to discover and understand the “precession of the equinoxes”.

The axis of the Earth, about which it spins once every 24 hours, wobbles against the much further away stars. This causes the sunrise on the equinox days each year (the two days when we have equal hours of day and night) to occur in slight different positions relative to the background stars.

Hipparchus came up with a figure of 26,00o years for the period of this wobble. Amazingly, this is pretty close to the value we have today.

Yes it’s hard to understand. And it was almost certainly even harder to work out in 300BC!

Hipparchus discovered this phenomenon by comparing his observations with those recorded in ancient Egypt, 2000 years earlier. He must have been having a GOOD DAY!




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