Night Sky in Trust

by Nick Martin

Nick Martin is a very active member of the Ayrshire Astronomical Society (www.ayrastro.co.uk) and I have enjoyed listening to his talks on several occasions including a special event at the Glasgow Science Centre Planetarium. This evening’s talk was an introduction to the night sky but still had plenty for everyone. He started his talk focusing at the centre of our solar system, the sun, and worked his way out into the universe.

Every star we see is a tiny twinkling spot of light except for one; our own sun. It is the only star we can see in detail and it can provide us with a considerable amount of information about stars in general. At this point Nick reminded everyone never to look at the sun without proper protection! The Ayrshire Astronomical Society has a special solar telescope with built-in filters that allow the sun to be observed in safety, but this cost several thousand pounds.

The surface of the sun is very turbulent with great prominences (eruptions from the surface) where charged gas is being blown off from the surface. Nick used a plasma sphere to model electric charged particles carrying a current to the surface of the sphere. He showed us that magnets not only attract but also repel, and much of the activity on the surface of the sun is due to interaction between magnetic fields. When the charged gas is emitted from the sun it travels through the solar system and hits the Earth's atmosphere causing the Northern lights (Aurora Borealis). It is the heat in the sun that causes all this activity. The surface of the sun is 6000°C and the centre is 15,000,000°C.

Many years ago scientists tried to work out what kept the sun burning. They calculated that if the sun was made of coal it would burn out too quickly and only last a few million years. It was only when an understanding of nuclear fusion was developed that the mechanism that kept the sun burning began to be understood. The sun works like a very inefficient hydrogen bomb; luckily, because if it was efficient it would simply blow up! As we discover when we use a bicycle pump, compressing gas creates heat. The compressed gas in the sun creates the conditions were a single hydrogen atom combines with three others to form helium. The weight of a hydrogen atom equals one, so you might think that the weight of a helium atom would equal four but it doesn't, it equals 3.98; 0.02 of the weight is "lost"! Using Einstein's famous equation E=mc2 where the energy generated (E) equals the mass (m) multiplied by the speed of light (c) squared, we find that our tiny loss of mass, 0.02, is multiplied by about 30 million multiplied by 30 million! We can see now that the conversion of hydrogen to helium creates a vast amount of energy and this is the process of nuclear fusion. Fortunately, most stars create this energy very inefficiently and take 9 billion years or so to use up the available fuel. Some of the very brightest stars have a core temperature of 100,000,000°C so run more efficiently and will therefore only last 5 million years or so.

The energy, in the form of gamma rays, released by fusion at the centre of the sun takes 125,000 years to reach the sun's surface; a bit like hot water rising when you boil a kettle. All this movement inside the sun creates enormous electrical charges which in turn create lots of magnetism. To give us some idea of the difference between the brightness of our sun and that of some of the brightest stars, Nick lit a night light candle to represent our sun and shone a very powerful million candle watt torch at us; a very clear demonstration. Of course the vast distance between our planet and the brightest stars makes them appear tiny compared to our own sun.

Nick then took us through the life of a star. Fast gas clouds in space are subjected to the shockwaves from a supernova (an exploding star at the end of its life). The shockwaves compress the gas in the cloud and cause it to form into more dense small clouds. Gravity then draws more gas into each cloud until they are sufficiently large and hot to start the process of nuclear fusion and start burning to form a cluster of small young stars of different sizes. Unused gas then shines with the light and heat from the young hot stars creating a nebula. Planets are too small to generate the heat necessary to start the fusion process.

Following this introduction, Nick used the program “Starry Night” to take us through the night sky.

We started our voyage at the moon looking at the dark areas known as the seas, which are in fact lava plains. These only exist on our side of the moon and do not on the other side. When the solar system was forming, clouds of dense gas condensed into planets and smaller proto-planets. The system was chaotic and there were many collisions and at some point when the Earth was still hot and soft, it was hit by an object about twice the size of Mars. The impact created a ring of rock debris around the Earth that coalesced into the moon. At this point the moon was 10 times closer to Earth than it is now and orbited the Earth about twice as fast. The enormous tides created in both the Earth and the moon by this close proximity caused tremendous volcanic activity. Big events elsewhere are in the solar system continued to send large fragments crashing into the Earth and Moon creating the many craters visible on the moon. On Earth, the very active weather and plate tectonics at have largely been disguised these impact craters and volcanic activity, but on the Moon they are still clearly visible. All this happened about 3.9 billion years ago and fortunately there are fewer asteroids around now. The moon is now geologically dead and the tides caused by the interaction between the moon and the Earth created friction that used up energy and slowed the moon down relative to the Earth causing it to slow down and move out to its current location.

Nick then took us out to Saturn. He pointed out Saturn's main feature, its rings, which form a complex and beautiful structure visible in a relatively small telescope. The Cassini spacecraft recently travelled through a gap in the rings which are only 1 km thick. Nick then took us further out in the solar system past Jupiter with its tremendous winds, coloured banding and red storm spot with its fascinating satellites such as Io, the most volcanic body in the solar system, and on to the outer planets.

We were then treated to a general tour through the night sky, looking at star constellations to help us find our way then star clusters, nebula, galaxies and other points of interest.

To finish his talk, Nick discussed the problems of light pollution. He demonstrated using his computer the effects of light pollution on what can be seen in the night sky. Even up here in Ayrshire we have to search to find good dark spots to view the night sky such as at Loch Doon. From Ayr itself much of the night sky is invisible and if you live in London very little is available to see at all. He pointed out that over 30% of the light from street lights goes straight up and lights up dust in the sky limiting your visibility. As more and more lights are added the situation is getting worse. The beautiful Milky Way is only visible in a really dark sky and many very young children have never had the joy of seeing it. New streetlight designs are available that limit the amount of wasted light and thus help reduce light pollution. Home security lights are essential for safety and crime reduction but are usually very badly positioned with over 50% of the light produced simply lighting up the sky; an expensive waste of electricity and a serious contributor to light pollution.

We would like to thank Nick Martin for his fascinating insight into the night sky. It has not been possible in this review to describe the detail of his talk as he interacted with the computer software. Many thanks indeed Nick, and we look forward to hearing you again in the near future.

John Rattenbury.