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UNIT NINE: Matter and Motion in the Universe

UNIT NINE: Matter and Motion in the Universe. Chapter 26 The Solar System Chapter 27 Stars Chapter 28 Exploring the Universe. Chapter Twenty-Seven: Stars. 27.1 The Sun 27.2 Stars 27.3 The Life Cycle of Stars. Chapter 27.3 Learning Goals.

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UNIT NINE: Matter and Motion in the Universe

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  1. UNIT NINE: Matter and Motionin the Universe • Chapter 26 The Solar System • Chapter 27 Stars • Chapter 28 Exploring the Universe

  2. Chapter Twenty-Seven: Stars • 27.1 The Sun • 27.2 Stars • 27.3 The Life Cycle of Stars

  3. Chapter 27.3 Learning Goals • Describe the events that occur at different stages in the life cycle of stars. • Apply knowledge of nuclear fusion to explain how elements are created in stars. • Discuss the significance of spectroscopy in classifying stars.

  4. 27.3 The life cycle of stars • A star, regardless of its size, begins its life inside a huge cloud of gas (mostly hydrogen) and dust called a nebula. • The Eagle Nebula is the birthplace of many stars.

  5. 27.3 The life cycle of stars • A protostaris the earliest stage in the life cycle of a star. • The Orion Nebula was the birthplace of these protostars.

  6. 27.3 The life cycle of stars • A star is born when temperature and pressure at its center become great enough to start nuclear fusion. • Once nuclear fusion begins, a star is in the main sequence stage of its life cycle.

  7. 27.3 The life cycle of stars • The time a star stays on the main sequence depends on the star’s mass. • High-mass stars burn brighter, and hotter, using up their hydrogen faster than low-mass stars.

  8. 27.2 The old age of Sun-like stars • As our sun grows old, its core begins to run out of hydrogen fuel. • Gravity then causes the core to contract, raising the temperature. • The hotter core pushes the outer layers of the star away, then star expands into a red giant.

  9. 27.2 The old age of Sun-like stars • With no more energy flowing outward, nothing prevents gravity from crushing the matter in the core together. • When hydrogen fusion stops, the core glows brightly and is called a white dwarf.

  10. 27.2 The old age of Sun-like stars • A planetary nebula forms when a star blows off its outer layers leaving its bare core exposed as white dwarf. • Planetary nebulae are one of nature’s ways of recycling the matter in old stars and distributing new elements.

  11. 27.3 Supernovae and synthesis of the elements • Scientists believe the early universe was mostly hydrogen, helium and a trace of lithium. • Heavier elements are created by nuclear fusion inside the cores of stars. • Nuclear fusion reactions are exothermic, releasing energy only up to iron. • When the core of the star contains mostly iron, nuclear fusion stops.

  12. 27.3 Supernovae and synthesis of the elements • If a star’s iron core reaches 1.4 times the mass of the Sun, gravity becomes strong enough to combine electrons and protons into neutrons. • During this brief period, heavier elements such as gold and uranium are created, as atomic nuclei are smashed together. • The core of the star collapses and the result is a spectacular explosion called a supernova.

  13. 27.3 Supernovae and synthesis of the elements • The Crab nebula is the remains of a supernova. • Chinese astronomers recorded it’s demise 1054 AD.

  14. 27.3 Examining light from stars • Spectroscopy is a tool of astronomy in which the light produced by a star or other object (called its spectrum) is analyzed.

  15. 27.3 Analyzing light from stars • A spectrometersplits light into a spectrum of colors and displays lines of different colors along a scale. • Each element has its own unique pattern of spectral lines.

  16. 27.2 Analyzing light from stars • In 1861, Sir William Huggins used spectroscopy to determine that the Sun and the stars are made mostly of hydrogen.

  17. 27.2 Analyzing light from stars • A few years later, Sir Joseph Norman Lockyer observed a line at the exact wavelength of 587.6 nm. • He concluded that this must be an undiscovered element and named it helium, after the Greek name for the Sun, Helios.

  18. Key Question: How can we use an H-R diagram to know where a star is in its life cycle? Investigation 27B Star Life Cycles and the H-R Diagram

  19. New Pathways in Science • Katherine Johnson began her career at the National Advisory Committee on Aeronautics (which later became NASA) in 1953. Johnson faced many hurdles. At the time, women weren’t permitted to attend briefings or put their names on reports.

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