Flamsteed Astronomy Society

‘From Egypt to Mars’ by Dr Marek Kukula - April 23, 2012

page 1 of 2

Report by Chris Gadsden

Marek Kukula is the Public Astronomer at the Royal Observatory Greenwich.  His speciality research subjects were the study of super-massive black holes and the evolution of galaxies.

The first point that Marek made was that the ancient astronomers did not have the problem that we have today of light pollution.  The blaze of stars over the clear air of the Egyptian desert would have been an awe-inspiring sight.

Paintings that have survived from ancient Egypt show that they had a good appreciation of astronomy.   By observing the skies they were able to keep track of time for planting crops at the right season. They were aware that the Sun was higher in the sky in summer than in winter, and that the ‘heliacal rising’ of Sirius (when Sirius rises just before the Sun at dawn) was a good indicator of when Nile flooding was due.

All the stars moved around the sky and this was proof to them that the Earth was stationary. The ancient Egyptians also observed that the path followed by the planets as they moved around the sky from night to night passed through the same set of constellations -- the Zodiac.   One assumption that was made was that the planets moved in perfect circles with the Earth at the centre. Sometimes though, the motion of the planets didn’t “behave” – this was when they observed retrograde motion which they couldn’t explain.

In the Hellenic era, Ptolemy (AD 90 – AD 168) tried to explain this phenomenon by developing the idea of epicycles – small circles upon larger circles, but this entailed many circles.  Prior to Ptolemy, Aristarchus of Samos (310 BC – 230 BC) had proposed a heliocentric theory, saying that if the Sun is at the centre with Earth and the planets moving around the Sun, then epicycles were not required.  But if the Earth was in motion why was there was no constant howling wind and how could birds fly etc?  These observations suggested that the Earth cannot move!

Aristarchus tried to measure the size of the solar system.  He devised a good method in theory but in practice it wasn’t possible for him to measure accurately the tiny angles involved.  Eratosthenes (c 276 BC – 195 BC) however, did measure the circumference of the Earth with amazing accuracy (within 2% of the correct value).

From this point Marek moved on to the Roman world and introduced Hypatia (c AD 350 – 415).  She was the first recorded female mathematician and philosopher.  She became entangled in religious conflict in Roman Egypt and was accused of being a witch.  She was dragged through the streets and brutally murdered by the mob in Alexandria.

Another notable mathematician, physicist and astronomer of this time was Archimedes (c 287 – 212 BC).  He is credited with, among other things, inventing the screw pump that bears his name, defining the principles of buoyancy, and he came very close to inventing the Calculus.

 

Dr Marek Kukula

[Pic Mike Dryland]

[Pic Mike Dryland]

Dendera Zodiac (schematic)

Apparent retrograde motion