S281, Planetary Science and Astronomy, An OU Course

By Malcolm Gibb

The middle of January and at last it arrives, a package with the units, projects, glossary, videos, a planisphere and all the paraphernalia for S281, the second level Open University course in Planetary Science and Astronomy. I was going to look at the stars, or so I thought! There is actually very little sky observation and is mostly confined to the six projects, which take about five hours spread between February and April. A quick glance through the books revealed a multitude of equations, graphs, tables, things called H-R diagrams and unfamiliar words which had me wondering if I had made the right choice this year, after all, I'm was doing this for fun.

Book one

'The stars and the interstellar medium' starts with our star, the Sun, and goes on to explore the properties of it and other stars. The range of stellar types is quite remarkable, massive blue stars, brown dwarfs, white dwarfs, red giants, supergiants, all snapshots of stars at different stages of their lives. I learned about red shifts and blue shifts, Cepheid and TTauri stars, red giants and white dwarfs and found out what a Hertzsprung-Russell diagram was. I had to recall a lot of physics from the first year science course, things like the electromagnetic wave and photon models of light, nuclear fusion, Planck's constant and a whole host of other things. The birth, life and death of the different types of stars were quite fascinating and the distances and sizes involved are mind-boggling. The fact that the light from the Sun takes just over eight minutes to reach us and four million tonnes of the Sun's mass is converted to energy every second, there is nothing on Earth to compare it with. Space is empty, or so I thought, until I reached Chapter 5 and the interstellar medium. Hot and warm intercloud mediums, dense clouds, HII regions, supernova remnants and planetary nebulae, is there any empty space?

Book two

The Planets, naturally enough, deals with all the planetary bodies in the Solar System, the likely origin of which was from material that formed a huge disc of gas and dust around the newly formed Sun. The layered structure, the evidence for the internal structure and the composition of the planets and their satellites are examined. Cratering and volcanism, which have shaped the surfaces of the solid planetary bodies and their satellites, are looked at. The evolution of the atmospheres of the terrestrial and the giant planets, the chemical reactions occurring within them and their weather systems are all considered

Book three

The Galaxies, deals firstly with our own Galaxy, the Milky Way, a galaxy of a hundred thousand million stars. This really stretches the imagination; the distances are so vast that astronomers invented their own units of distance, light years, parsecs and kiloparsecs(kpc). The Milky Way is at least 100,000 light years across, or put another way, about 30 kpc, which is easier to say than 1,000,000,000,000,000,000km. Then there are the constituents of it, stars, gas, dust and dark matter along with minor constituents that contribute little to the mass but play an important role in determining its nature. But dark matter, are they kidding? It's invisible, it has not been directly detected yet, but it's known to exist by its gravitational effect on matter that can be seen. The disc, the halo and the nuclear bulge are all examined along with open clusters, globular clusters, high velocity clouds and at the heart of the Milky Way, Sagittarius A* the unresolved radio source which one theory states, could be a black hole at the very centre of our Galaxy.

Moving on to other galaxies we are introduced to the Hubble classification scheme for galaxies. The four major classes; elliptical, lenticular, spiral and irregular with lenticular and spiral being subdivided into barred and unbarred varieties then the various classes and subclasses are divided into a number of Hubble types denoted by a combination of letters and numbers. For example, SBa would be a barred spiral galaxy with tightly wound arms and a large central bulge, whereas Sc would be an unbarred spiral galaxy with loosely wound arms and a relatively small bulge. All very straightforward until you come to peculiar galaxies, cD galaxies, binary galaxies, proto-galaxies, primeval galaxies, interacting galaxies and shell galaxies. Then the next chapter, Starburst and Active Galaxies, with names like Seyfert galaxies, quasars, BL Lac objects and radio galaxies, all powered by an engine and giving out large amounts of energy. After that come massive black holes, the Schwarzschild radius and the Eddington limit with a quick look at hot dark matter, cold dark matter and large-scale motions, which the book tells me, are co-ordinated peculiar motions. By this time my mind seems to be an empty space and there is more to come!

Book four

Cosmology, with Hubble's law and the expansion of the Universe, the age of the Universe, the Einstein-de Sitter model and the resolution of Olber's paradox 'why is the sky dark at night?' The Big Bang theory with the analogy of an expanding balloon, a closed Universe with a Big Crunch and the possibility of a Big Bounce. The best evidence yet for the Big Bang theory is the discovery by physicists of Cosmic Microwave Background Radiation which does not vary with time nor across the sky, it comes from all parts of the Universe exactly as predicted, the remnants of radiation that came from the fireball that accompanied the Big Bang. An open Universe which would keep on expanding forever, eventually, however all the star forming material gets used up, the existing stars die, galaxies become massive black holes and all the while the Universe, cold and lifeless, keeps on expanding. Curiously, I understood this part of the course easier than the previous book, or perhaps it was because of the previous one that I understood this. By this time I think the authors were running out of new words to baffle us with. This quote towards the end of book four would indicate that they are getting tired 'it becomes more natural to think of space as a (normally) completely uniform distribution of stuff, rather than as nothing. It's comforting to know that they too get stuck for words at times and can regress to a more rudimentary description.

One thing I haven't mentioned is the set book, 'Images of the Cosmos' which forms part of the course. This is an excellent book full of colour photographs and diagrams. The photographs are mainly from NASA and the Hubble telescope and where actual photographs can't be obtained, artist's impressions are used. Useful tables of facts and figures are also included.

I enjoyed the course, I passed the exam, but it was much harder than I imagined it would be. Before starting, I had a passing interest in astronomy and any knowledge I had was gleaned from newspapers and magazines such as the New Scientist. Now my interest is such that I became involved in founding the Association of Falkirk Astronomers. Go on, try it; S281 is an excellent course for anyone keen to further his or her knowledge of the Universe.