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STARS DISTANCES IN THE SOLAR SYSTEM • Our Sun is the closest star to us. • Distances in the solar system are so big that we use a large unit of measurement. • A LIGHT YEAR is the distance light travels in one year. WHAT IS A LIGHT YEAR? Consider the following: – Light travels 300 000 km every second. – There are 31 536 000 seconds in a year Distance = speed x time – Therefore, if we multiply the numbers together, we get 10 trillion km, or 10 000 000 000 000 km! LIGHT YEARS, CONT’D • The closest star to us, Alpha Centauri A , is 4.3 light years away. • This is equivalent to 43 000 000 000 000 km away from us! WHAT IS A STAR? STAR: A collection of matter that emits huge amounts of energy. STARS are classified based on four characteristics: 1.Colour 2.Temperature 3.Size 4.Brightness COLOUR & TEMPERATURE COLOUR Temperature Range (C) • Stars glow because they are very hot.– 50 000 Blue (ex. Zeta Orionis) 25 000 • Rigel) The colour Bluish-White (ex. 11that 000 an – 25 000 tells White (ex. Sirius) object glows 7500 – 11 000 us how hot it is. Yellowish-white (ex. 6000 – 7500 • Cool stars glow red; Polaris) very hot stars glow Yellow (ex. Sun) 5000 – 6000 blue. Orange (ex. Arcturus) 3500 – 5000 Red (ex. Betelgeuse) 2000 - 3500 SIZE OF STARS GIANTS AND DWARFS • When a star begins to reach “old age” the pressure inside runs out as all the hydrogen runs out. • As the star gets older, it swells in size. • Our Sun will become a Red Giant as it runs out of fuel. • When it “dies” it will become a white dwarf. • Our Sun is bigger than 95% of the stars in the Universe. • The Size Of Our World OTHER ASTRONOMICAL STUFF… SUPERNOVA • An enormous explosion when a large star dies. • When all the hydrogen is used up the core collapses • The absence of pressure causes a neutron star or a black hole. • The explosion can be bright enough to see during the day! OTHER ASTRONOMICAL STUFF… NEUTRON STAR • These stars are ten times bigger than our Sun. • It become a dense core of neutrons. • A PULSAR is a type of neutron star. OTHER ASTRONOMICAL STUFF… BLACK HOLE • These are stars thirty times bigger than our Sun. • Small, very dense object with an extremely strong gravitational pull. • Nothing can escape from it; not even light. OUR SUN • The Sun’s energy comes from NUCLEAR FUSION, a reaction that takes place under high temperature and pressure. • Nuclear Fusion OUR SUN The Sun has multiple layers: • Core: Nuclear fusion takes place here, and temperatures can reach 15 million °C. • Photosphere: The surface of the Sun, made up of moving gases; average temperature of 5500 °C. Sunspots occur here. OUR SUN • Chromosphere: the inner atmosphere of the Sun • Corona: The hot outer layer of the Sun; temperatures reach 1 million °C. OUR SUN Other features of the Sun: • Solar Prominence: an explosion of glowing gases from the chromosphere that can last for weeks and reach 40,000 km high. • Solar Flare: Like a solar prominence, but the gases travel into the corona, and last only a few minutes. GALAXIES & STAR CLUSTERS • Galaxy: a collection of gas, dust, and hundreds of billions of stars. • Our Sun is located in the lesspopulated spiral arm of the Milky Way. GALAXIES & STAR CLUSTERS • There are approximately 400 billion stars in our galaxy. • The majority of the stars are located in the central bulge. Unusual Galaxies • Quasars: Astronomical objects that look like very faint stars, but emit hundreds of times more energy than entire galaxies. • Scientists do not know the reason for the intense light output. STAR CLUSTERS • Star Clusters: groups of stars that are close together and travel as a group (as few as 10 or as many as 1 million). Ex. Pleiades