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1. Identify the chemicals that make up stars. 2. Understand how different natural forces affect how stars look. 3. Explore how stars have constantly changed outer space over time. A star is a hot glowing sphere of gas that produces energy by fusion held together by gravity. Fusion means ‘joining together’. Astronomers say… Without stars, there would be no planets and no life. Humans consist of the elements that the stars have made. Have you ever been caught in the middle of a large crowd? How did it feel? If you remember feeling hot or pressured, this is similar to what happens to hydrogen atoms in the core of a star, where the temperature and pressure are very high. Gravity forces the hydrogen atoms together so strongly that they fuse. When that happens, a new element called helium is formed and a little bit of energy is released. We call that energy starlight. How bright the star looks to us on Earth depends on 3 things: 1. Star size 2. Distance from Earth 3. Star temperature A star’s temperature can be determined by its colour. Colours hottest to coolest: Blue/white yellow orange red. NEBULA: A large cloud of gas (helium and hydrogen) and dust which forms into a star. Dust and gas particles exert a gravitational force on each other which keeps pulling them closer together. As the particles pull closer together the temperature increases. At 10,000,000o C fusion takes place and energy radiates outward through the condensing ball of gas. Fusion uses up a star’s hydrogen supply rapidly causing the core to heat up and the outer temperature to fall. The star expands and becomes a red giant. As the core uses up its helium supply, the outer layers escape into space and the remaining core is white hot and called a white dwarf. When no more material is left in the core it explodes into a supernova. Smaller stars become neutron stars and most of the massive ones will collapse into a black hole. Neutron star Nothing (not even light) can escape the gravity of a black hole. Heavy inner core. Radiation zone: Energy bounces back and forth before escaping. Convections zone: Cooler layer of gas that is constantly rising and sinking. Photosphere: Bright source of much of the light we see. Chromosphere: Active layer which is home to many significant displays. Cool dark areas on the sun’s surface, first discovered by Galileo. They appear and disappear. 15 February 1564 – 8 January 1642 Galileo was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and observations of the stars and planets. A replica of the earliest surviving telescope attributed to Galileo Galilei. Violent eruptions near a sunspot which suddenly brighten and shoot outward at high speed.