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In 1054 a star appeared that was so bright it was visible in broad daylight for a short period of time, and was visible at night for the following six months. Accounts were recorded by different cultures all over the world. It was later determined that this was a supernova, or an exploding star. In the past they were called "new stars," or "guest stars," because they appeared suddenly and weren't usually seen for a very long period of time. The remnants of that 1054 supernova are seen by looking at the Crab Nebula with special equipment. A nebula is a cloud of gas and dust formed by a supernova.
All atoms have a built-in force of repulsion. To overcome this force of repulsion, high pressure and high temperatures are required to fuse atoms together. The process of fusing atoms together is known as nuclear fusion. As we speak, for example, our sun is constantly fusing three hydrogen atoms to form one helium atom, a process that releases large amounts of energy. All atoms (with the exception of hydrogen, some helium, and some lithium) are formed on the inside of stars by this process. At the right is an Extreme ultraviolet Imaging Telescope (EIT) image of the sun. Can you see it fusing hydrogen to form helium?

Image courtesy of NASA.

In a future Sci-ber text page, you will explore the different life cycles of stars. Hopefully you will recognize the relationship between the mass of the star and the mass of the elements produced. In other words, when a star has a large mass, it exerts a larger pressure on the atoms that make it up, and therefore heavier elements are able to form. Additionally, you noticed that only the most massive stars become supernovas. During a supernova there is so much energy released that the high temperatures will fuse heavier elements. So the more massive a star, the more massive the elements that it produces. The heavy elements found on Earth are most likely from a very massive and ancient star. Light elements are therefore produced by lighter stars in the universe.
When comparing masses of stars, we see that our sun has a fairly small mass. Would you expect our sun to produce lighter or heavier elements than another star that has more mass? Check your answer.
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Updated October 24, 2008 by: Glen Westbroek

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