Picturing the Planets

Talk by Susan Cartwright – Sheffield University

This was a specially commissioned talk by Susan.  A member had asked me for a talk on the history of astronomy.  Obviously a vast area and we had to narrow it down so we agreed on the solar system.

The talk answered some questions for both beginners and seasoned members.  It took us from ancient man’s observations of the night sky to scientists’ views of other solar systems in the universe.

Man has always looked up and wondered what they were seeing.  They worked out what were stars and what were planets.  Man felt the need to construct a calendar and first used the stars and planets.  They tried to use the moon’s phases to construct a calendar but found its cycle “didn’t fit”  Susan took us through several worthy scholars who had a go.  She made it humorous  as well as factual and explained why we know that ancient man did what they did.  After all nothing was written down as writing had not been invented.  Drawings however, were another matter and scholars could pass on their knowledge by word of mouth to those coming after. 

In the 3rd century BC Aristarchos of Samos  did discover that the sun was the centre of the solar system but by the advent of religion in the first century AD that all changed.  Ptolomy, a greek, tried to devise a model with Earth off centre to make his model “fit”.  For fifteen centuries man tried to make the concept of the earth being the centre of both the solar system and the universe “fit” into their idea of what was “right”.  Susan made this sound funny, but in reality this was what was being given out as correct.

It wasn’t until Copernicus, in 1543, that we eventually had someone who could explain things as they really were.  By this time printing had been invented and he was able to publish his findings.

With Galileo and the telescope at last we had proof that the planets orbited the sun.  What a lot of learning was missed in the intervening centuries! 

Other notable scholars began to publish and we learnt about elliptical orbits.  Newton came next with his F=GMm over r2 predicting Haley’s Comet.  Halley had observed the comet, named after him, but Newton correctly predicted the comet’s return.  Halley did not live to see it.

It wasn’t until 1727 that James Bradley proved the earth moved!!  He succeeded Edmund Halley as Astronomer Royal and his findings were hailed as “the most brilliant and useful of the century”.

Bessel in 1838 was the first astronomer to work out the distance from the sun to another star by the parallax method.

William Hershel, then in 1781, quite by accident, discovered Uranus.  He was funded by George III and wanted to name the planet “George”.  but as the planets were named after Roman gods (Earth excepted) it was refused – hence the name Uranus.

Galle is credited with the discovery of Neptune.  Urbain Le Verrier had predicted the existence of another planet and sent his co-ordinates to Galle who found the planet.

Tombaugh in 1930 found Pluto.  At the time of its discovery is was named a planet, but we all know what happened subsequently.  He also discovered many asteroids.

The list of notable discoveries is endless.  We can look back on all this with hindsight and smile at the people involved, but they were all pioneers.

Susan took us forwards into the space age with images of systems around other stars and told us that our model of 4 rocky planets and 4 gas giants wasn’t the norm.  She told us of planets orbiting Kepler that were quite different to our solar system with gas giants orbiting close in to the star.

There is so much more to discover out there with Quantum Mechanics etc that she would have been talking for ever.  As it was her talk lasted 2hours and she was generously thanked at the end.  I have emailed her with some feedback and to tell her how much her talk was appreciated.

Marilyn Bentley