How do stars work?

Our ancestors had no problem with the idea that the sun would rise and set every day, providing light and warmth, forever.

Things in the sky things could be eternal, whereas at ground level they weren't. However, in the 18th and 19th centuries, advances in science started raising difficult questions. At that point it was believed the entire universe was obeying the same laws. Therefore, if the sun was providing light and heat to us and the other planets, where was it getting the energy?

The question became even more intriguing in the light of the discoveries made by geologists. They found more and more proof the earth was not thousands of years old, it had to be many millions of years old.

The oldest fossils known at the time were in rocks some 500 million years ago, from what became known as the Cambrian period. These rocks were first studied in Wales, which was called Cambria by the Romans.

For living things to have been swimming in the earth's oceans since then, the sun had to be providing a more or less steady level of heat and light over all that time. More recently, signs of living things have been found in rocks around four billion years old, only 500 million years after our planet, the other planets and the sun formed.

The 19th century was the "Age of Steam" and the heat to provide that steam was provided by burning coal. It is not clear whether that was a serious calculation or something done for fun, but someone calculated if the sun were a ball of coal, it would have completely burned away in 10,000 years or so. Of course, that is, assuming oxygen was available to make combustion possible, which, of course, there was not.

Another, more serious calculation was based on the heat generated when a cloud of gas and dust collapses to form a star. The energy released by the collapse and compression of the material would release a lot of heat. However, as in the case of the "coal sun", the heat would not last long enough. The problem 19th and early 20th century physicists faced was they knew little about atomic processes and their capacity for energy production, which is where the solution lay.

Last Christmas, my stocking contained a lovely old science book, titled "The Story of Creation", about the appearance and evolution of life on Earth since the Cambrian era, 500 million years ago. The book was published in 1902. The author realized the importance of a stable sun and discussed the difficulty in explaining where it was getting its energy. He mentioned new knowledge about radioactive elements such as radium, which have large, unstable atoms, which break into smaller ones, releasing energy. He did point out that the sun is made of mostly hydrogen and helium, not radium, but raised the idea the solution lies at the atomic level.

Finally, around 1920, Arthur Eddington proposed that stars obtain energy through nuclear fusion, the merging of light atoms such as hydrogen to form larger ones. The question was how to find out if this idea is correct.

Fortunately, there were two pieces of evidence to be searched for. High-energy nuclear fusion reactions produce ghostly particles called neutrinos. These pass through almost anything, so escaping from the sun was not an issue. Similarly, they pass through the Earth too. A neutrino detector, a big tank of dry-cleaning fluid, was set up deep in a mine, and neutrinos were detected.

The second item of proof is the relative proportions of various elements in the dust between stars and in the stars themselves. These elements are the waste products of energy production in stars now dead.

If our fusion ideas are correct, we can calculate those relative proportions and then compare them with observations. They matched. However, we still have a lot to learn about energy production in stars, but we know the essentials.

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• After sunset, Venus shines brightly low in the southwest.

• Saturn lies in the south and Jupiter is rising in the northeast. Mars rises about three hours later. • The Moon will be new on Nov. 30.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.