1.9 What are we made of? 9 November, 2013

Key words Nuclear fusion Life cycles

Stars and Earth stuff Scientist can now spread light into spectra and study the colour present If light is shone through different elements then each produces its own unique finger print Dark lines show areas where light is absorbed Analytical scientists use this information to determine what chemical are present in a sample

The sun The sun is a light source. Its light tells us how hot it is, and what it is made of When astronomers first looked at the spectrum of sunlight, they were amazed to find similar patterns to those seen in the laboratory They looked at other stars – the same 92 elements everywhere

Nuclear fusion Scientists once struggle to understand the Sun It could not be a ball of gas on fire as it would have burned up long ago It was found that atoms have central cores called nuclei, joining these together releases a lot of energy and new elements are created

A star is born Gravity pulls a star together from hydrogen gas The hydrogen gas collapses, faster and faster Some of the nuclei collide fast enough to overcome repulsion Fusion begins Fusion releases heat to keep the temperature high, the nuclei fast and gravity balanced

Heavy elements The most common element in the Universe is hydrogen In stars, fusion continues to make heavier and heavier elements up to iron When a star explodes in a supernova all the heavier elements are formed This is what you and I are made of – star dust!

Questions How can scientists find out about (a) temperature and (b) chemical elements in the outer layers of a star How do you know that the Sun is not a ball of gas on fire Scientists believe that hydrogen, helium and a little lithium were the only elements in the Universe before they were stars. There are 92 natural elements on Earth. Where did they come from?