Wonders of the Universe - Brian Cox [40]
Once safely returned to Earth, the treasures from the Moon, including rock samples, were painstakingly analysed at a high-security laboratory, and are still being used for analysis today.
NASA
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Again and again we find there is much to discover in our solar system, but there are never new elements to unearth.
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This false-colour photograph of Neptune was taken by Voyager 2. This image has enabled scientists to discover that the planet is rich in organic molecules such as methane.
So what about the rest of the Universe? How universal are these elements across the far reaches of the cosmos? Could it be that there are places in the distant Universe where the laws of physics are different? This is a legitimate question – we shouldn’t simply assume that everything at the edge of the visible Universe, billions of light years away, operates exactly as it does here, no matter how persuasive the arguments from theoretical physics. Experiment and observation are the ultimate reality check. It may seem impossible to presume that we could ever answer this question directly and discover what the stars are made of, because they are so far away (they may indeed remain untouchable forever), but in fact we knew what the stars were made of long before we got our hands on that first piece of lunar rock
WHAT ARE STARS MADE OF?
Over a simple campfire I recreated the experiments of Gustav Kirchhoff and Robert Bunsen that made such a major impact in the development of quantum theory. Just as they discovered 150 years ago, when I threw the copper into the fire it burned with a spectacular blue flame.
The Sun, the burning star at the heart of our solar system, is 150 million kilometres (93 million miles) away from Earth. Beyond that, the nearest known star, the red dwarf Proxima Centauri, requires a journey of over four light years or forty thousand billion kilometres (twenty-five thousand billion miles). We have learnt a lot about Proxima Centauri since it was discovered by Robert Innes at the Cape Observatory, in South Africa, in 1915. It is thought that Proxima Centauri is part of a triple star system with its neighbouring binary star system, Alpha Centauri A and B, and although it cannot be seen with the naked eye, we have been able to measure its mass and diameter and chart its brightness across the last 100 years. Despite the fact that our only contact with these neighbouring stars, and with any star other than our Sun, is the light that has crossed the Universe to reach us, we have been able to go much further than simply cataloguing their vital statistics. We can measure the precise constituents of any and every visible star in the sky, because encoded in the light that rains down on Earth is the key to understanding what they are made of. It is all made possible by a particularly beautiful property of the elements.
The tale of how we learnt to read the history of the stars in their light began with the work of Isaac Newton in 1670. In his ‘Theory of Colour’, Newton demonstrated that light is made up of a spectrum of colours, and that with nothing more complicated than a glass prism you can split the white light of the Sun into its colourful components. Almost 150 years later, the German scientist Joseph von Fraunhofer made a startling discovery about the solar spectrum whilst calibrating some of his state-of-the-art telescopic lenses and prisms. Lying within the solar spectrum, Fraunhofer documented the existence of 574 dark lines; there were literally hundreds of gaps – missing colours in the Sun’s light. Unaware of the significance of this discovery at the time, Fraunhofer carefully mapped their positions in great detail. He went on to discover black lines in the light from the Moon and planets, and from other stars. These are now known as Fraunhofer lines.
Further work by two more of the great German scientists of the nineteenth century, Gustav Kirchhoff and Robert Bunsen (perhaps best known to schoolchildren everywhere as the