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8.3 EXPLORING OTHER H O MSTARS EWORK: PAGE 349 # 1, 3, 8 KEY CONCEPTS: • A star’s apparent brightness depends on its luminosity and distance from Earth. • Hertzsprung and Russell independently discovered that each type of star has specific properties. They organized their findings into what is now called a Hertzsprung and Russell ( H-R) diagram KEY CONCEPTS: • The main sequence is a narrow band of stars on the H-R diagram that runs diagonally from the upper left ( bright, hot stars) to the lower right ( dim, cool stars). About 90 percent of stars are on the main sequence, including the Sun. • A star’s position on the main sequence is determined by its initial mass. KEY CONCEPTS: • A star will become a white dwarf, a neutron star, or a black hole, depending on its initial mass. • Canadian researchers contribute to our understanding of space. HOW BRIGHT IS THAT STAR? • Luminosity is a measure of the total energy output a star radiates/second • Joules/second • Absolute magnitude is the brightness of a star • Absolute magnitude of the sun is 4.7 • A star’s apparent magnitude (how bright it appears on Earth) depends on its brightness and distance from Earth STAR PROPERTIES: COLOUR • Astronomers use a star’s colour to determine its surface temperature • Sun’s photosphere = 6000°C Yellow • Blue stars are very hot • 21 000 – 35 000°C • Red stars, not so much • 3300°C STAR’S PROPERTIES: COMPOSITION • Different stars emit different light • Light can be analyzed by a spectroscope to determine its wavelength and spectral lines • The star’s spectral lines identifies the elements within the star’s photosphere INQUIRY PRACTICE! • Try: Inquiry Investigation 8-B page 352 • Answer questions 1-5 (Analyze & Interpret) STAR PROPERTIES: MASS • Determining the mass of stars was impossible until astronomers discovered most stars seen from Earth are Binary stars • 2 stars that orbit together (same orbit) • By measuring orbit size and time lapsed, it is possible to calculate “solar mass” • Sun = 1 solar mass • Exception: The Sun is not binary HERTZSPRUNG-RUSSELL DIAGRAM • In the 1920’s, 2 astronomers looked for patterns in star data • Independently, they observed that star types have characteristic properties that are related: • Temperature • Colour • Luminosity HERTZSPRUNG-RUSSELL DIAGRAM HERTZSPRUNG-RUSSELL DIAGRAM THE “MAIN SEQUENCE” • Central band of stars stretching across, down H-R diagram • Accounts for 90% of the stars viewed from Earth EVOLUTION OF A STAR • Stars can shine for billions of years with little change • However, the radiate massive quantities of energy they can’t last forever! • Eventually they will run out of fuel • In the final stages of a star’s life, it will become • A white dwarf, or • A neutron star, or • A black hole • The fate of the star depends on its initial mass STELLAR COMPARISON • Make a table in your notes comparing: • • • • • Low-mass stars Intermediate-mass stars High-mass stars (massive) Neutron stars Supernovas