April 23, 2012

From Egypt to Mars

Dr Marek Kukula

Report by: Chris Gadsden

Apparent retrograde motion

Dendera Zodiac (schematic)

Marek Kukula

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 Earthcannot 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.

A significant invention dating from about 2000 years ago is the Antikythera Mechanism which was discovered only 100 years ago in an ancient shipwreck. It was a device that used a sophisticated system of gear-wheels to display astronomical cycles and can be considered to be the earliest forerunner of the modern computer.

Marek went on to talk about the Polish astronomer and mathematician, Nicolaus Copernicus (1473 – 1543) who was a proponent of the view that the Earth rotates daily about its axis and yearly around the sun. This theory, which was rejected by the Roman Catholic Church, resulted in much simpler mathematics to explain the motion of the planets.

Next on the scene was Johannes Kepler (1571 -1630). He was the first to demonstrate that the planets did not move in circles around the Sun, but rather followed an elliptical path. Kepler’s discoveries were founded on the wealth of detailed observations made by Tycho Brahe. Kepler’s analysis of Tycho’s measurements of the positions of Mars was particularly important because the shape of Mars’ orbit is the most elliptical of all the planets and impossible to explain as a circle. Also, Kepler described the relationship between the time-period of planetary orbits and their distance from the Sun, which means all the distances can be calculated as soon as any one is known.

Another eminent mathematician and philosopher of this era was Galileo Galilei (1564 – 1642) who is credited with the first use of the telescope in astronomy. Using his telescope he discovered four moons of Jupiter and observed their rotation around the planet, proving that not all the motions of the heavens are around the Earth (or Sun depending on one’s persuasion). His telescopic observations of the phases of Venus clearly supported the theory of a Sun-centred solar system. As a result of publishing these findings he incurred the wrath of the Catholic Church, was found guilty of defending Copernicus too much, and spent the final years of his life under house arrest.

Marek mentioned two more distinguished scientists: Isaac Newton (1642 – 1727) and James Bradley (1693 – 1762). Their observations and theories finally dispelled any doubts about the Sun being the centre of the solar system. Newton showed that the same force which causes an apple to fall to Earth also holds the Moon and planets in orbit. Newton’s Laws are used to this day to calculate the flight path of space shots, including probes sent to Mars. James Bradley, the third Astronomer Royal, was the first to show by direct observation that the Earth is in motion around the Sun. His high-precision measurements detected the effect on the observed positions of stars caused by the Earth’s velocity through space, an effect he called the ‘aberration of light’.

Finally, returning to Egypt, Marek recounted “A Cautionary Tale” concerning an eminent British astronomer and pioneer photographer, Charles Piazzi Smyth (1819 -1900). He was Astronomer Royal for Scotland from 1846 to 1888 and did much outstanding work in astronomy. He went to Tenerife and made many astronomical measurements in the clear air, high up in the mountains. In fact he is known as the “father of mountain observatories”.

However, Piazzi Smyth was obsessed by the Egyptian pyramids at Giza. He made many observations of the pyramids measuring their size, angles and dimensions of the internal passages. All this was because he was convinced that the pyramids held many physical and astronomical constants, e.g. the size of the Earth, the value of pi, the inch unit of measurement. These values he suspected were encoded in the dimensions of the pyramids. Flinders Petrie (1853 – 1942), did not like these ideas and said that many of the measurements did not tally. Those who disagreed with him he labelled “Pyramidiots”.

To bring the lecture to a close Marek projected some slides of Mars showing some unusual shapes; these could be interpreted as being pyramids. And some meteorites recovered in Egypt, dating from 12,000,000 years ago, on examination revealed that the air trapped inside the stones was identical to the Martian air – from Mars to Egypt!

This was a fascinating lecture, crammed full of interesting facts and figures which promoted a lively Q & A afterwards.