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4/20/2017 Foundations of Astronomy | 13e Seeds Keep your voting card ready Phys1411 – Introductory Astronomy Instructor: Dr. Goderya © Cengage Learning 2016 Announcements/Reminders • Exam 3: Thursday 27th April Chapters 8, 19, 20, 21, 22 Review the question I put on the power points and the pretest in the homework. Pretest is just for practice, I don’t count them for grade. I may give you a small sample question set. Chapter 20 and 21 • Lab for this week is uploaded online: Due April 25th. • Homework for chapter 19 due April 28th • Homework for chapter 20 due April 28th • Homework for chapter 21 due April 28th • Homework for chapter 22 due April 28th Chapter 20 1. Earth Formation A. Layers B. Formation 2. The Solid Earth A. Earth's Interior B. The Magnetic Field C. Earth's Active Crust Earth: The Active Planet Moon: Airless World Chapter 21 1. The Moon A. The View From Earth B. Highlands and Lowlands C. The Apollo Missions D. Moon Rocks E. The History of the Moon F. The Origin of Earth's Moon 3. The Earth’s Atmosphere A. Origin of the Atmosphere B. Human Effects on Earth's Atmosphere © Cengage Learning 2016 © Cengage Learning 2016 1 4/20/2017 20-1: Formation of Earth 20-1: Formation of Earth The four stages of Terrestrial planet development are illustrated for Earth. The four stages of Terrestrial planet development are illustrated for Earth. 1.Differentiation produces a dense core, thick mantle, and low-density crust. 2.The young Earth was heavily bombarded in the debris-filled early solar system. 3.Flooding by molten rock and later by water can fill lowlands. 1 4.Slow surface evolution continues due to geological processes, including erosion. 2 © Cengage Learning 2016 20-2: Earth: Structure and Layers Earth’s surface is marked by high continents and low seafloors. The crust is only 10 to 60 km thick, and interior to that are a deep mantle and an inner core. 4 © Cengage Learning 2016 20-2: Earth’s Interior Direct exploration of Earth’s interior (e.g. drilling) is impossible. Earth’s interior can be explored through seismology: earthquakes produce seismic waves. Two types of seismic waves: Pressure waves: Seismic waves do not travel through Earth in straight lines or at constant speed. They are bent by or bounce off transitions between different materials or different densities or temperatures. Such information can be analyzed to infer the structure of Earth’s interior. Shear waves: Particles vibrate back and forth Particles vibrate up and down © Cengage Learning 2016 20-2: Seismology 3 20-2: Earth’s Interior Temperature Basic structure: Solid crust Solid mantle Liquid core Solid inner core Earth’s interior gets hotter towards the center. Earth’s core is as hot as the sun’s surface; metals are liquid. 2 4/20/2017 20-2: Earth’s Interior Temperature Test Your Learning? Basic structure: Melting point = temperature at which an element melts (transition from solid to liquid) Earthquakes are an important tool for scientists because their vibrations a) influence the Earth's orbit about the Sun => Inner core becomes solid b) allow the study of the Earth's internal structure c) inform us of the mass of the Earth d) are used to predict the future of plate tectonics Melting point increases with increasing pressure towards the center 20-2: The Magnetic Field © Cengage Learning 2016 http://hea-www.harvard.edu/~pgreen/ 20-2:The Role of Earth’s Magnetic Field • Earth’s magnetic field is a direct result of its rapid rotation and its molten metallic core. (a) Earth’s magnetic field dominates space around Earth by deflecting the solar wind and trapping high-energy particles in radiation belts. The magnetic field lines enter Earth’s atmosphere around the north and south magnetic poles. (b) Powerful currents flow down along the magnetic field lines near the poles and excite gas atoms to emit photons, creating auroras. Colors are produced as different atoms are excited. Note the meteor (shooting star). © Cengage Learning 2016 © Cengage Learning 2016 Test Your Learning? The Earth's magnetic dynamo is caused by a combination of convection in its molten core and Test Your Learning? Particles from the Sun interact with the Earth's magnetic fields to produce a) the Earth's orbit around the Sun a) b) the Earth's rotation b) dangerous ultraviolet radiation c) lunar tidal action c) hydrogen and helium d) the aurora borealis d) protons and electrons © Cengage Learning 2016 http://hea-www.harvard.edu/~pgreen/ the aurora borealis © Cengage Learning 2016 http://hea-www.harvard.edu/~pgreen/ 3 4/20/2017 20-2: The Active Earth 20-2: Tectonic Plates Earth’s crust is composed of several distinct tectonic plates, which are in constant motion with respect to each other Plate About 2/3 of Earth’s surface is covered by water. tectonics Mountains are relatively rapidly eroded away by the forces of water. Evidence for plate tectonics can be found on the ocean floor © Cengage Learning 2016 20-2: Plate Tectonics … and in geologically active regions all around the Pacific © Cengage Learning 2016 20-2: Active Zones Resulting from Plate Tectonics Tectonic plates move with respect to each other. Where plates move toward each other, plates can be pushed upward and downward Where plates move away from each other, molten formation of mountain lava can rise up from ranges, some with volcanic activity, earthquakes below volcanic activity 20-2: Earth’s Tectonic History Volcanic hot spots due to molten lava rising up at plate boundaries or through holes in tectonic plates © Cengage Learning 2016 Test Your Learning? When two continental plates collide, the likely result is that a) folded mountains are created b) a hot spot is produced c) very young rocks emerge from below the crust d) a crater is formed © Cengage Learning 2016 © Cengage Learning 2016 http://hea-www.harvard.edu/~pgreen/ 4 4/20/2017 20-3 - The Atmosphere 20-3 The Structure of Earth’s Atmosphere Earth had a primeval atmosphere from remaining gasses captured during formation of Earth Composition of Earth’s atmosphere is further influenced by: Atmospheric composition severely altered ( secondary atmosphere) through a combination of two processes: 1) Outgassing: Release of gasses bound in compounds in the Earth’s interior through volcanic activity 2) Later bombardment with icy meteoroids and comets © Cengage Learning 2016 20-3 A Common Misconception • Misconception: There is life on Earth because of oxygen – Truths: • Oxygen was not part of Earth’s primeval atmosphere • There is oxygen in Earth’s atmosphere because of life • Photosynthesis by plants is what keeps steady supply of oxygen in Earth’s atmosphere © Cengage Learning 2016 3 – B Climate and Human Effects on the Atmosphere (c) The concentration of CO2 in Earth’s atmosphere as measured in Antarctic ice cores remained roughly constant for thousands of years until the beginning of the Industrial Revolution around the year 1800. Since then it has increased by more than 35 percent. Evidence from proportions of carbon isotopes and oxygen in the atmosphere proves that most of the added CO2 is the result of burning fossil © Cengage fuels. Learning 2016 • Chemical reactions in the oceans, • Energetic radiation from space (in particular, UV) The ozone layer is essential for life on Earth since it protects the atmosphere from UV radiation • Presence of life on Earth The temperature of the atmosphere depends critically on its albedo = percentage of sun light that it reflects back into space Depends on many factors, e.g., abundance of water vapor in the atmosphere © Cengage Learning 2016 20-3 Climate and Human Effects on the Atmosphere The greenhouse effect: (a) Visual-wavelength sunlight can enter a greenhouse and heat its contents, but the longer-wavelength infrared radiation cannot get out. (b) The same process can heat a planet’s surface if its atmosphere contains greenhouse gases such as CO2 . © Cengage Learning 2016 Common Misconceptions • Misconception: Greenhouse effect is bad for Earth – Truths: • Earth has always had a greenhouse effect • CO2 is not the only greenhouse gas • Also includes water vapor, methane and other gases • Misconception: Ozone is bad – Truth: The ozone layer is what protects Earth’s surface from harmful UV radiation © Cengage Learning 2016 5 4/20/2017 20-3 Global Warming 20-3 Global Warming (cont’d.) • The average temperature on Earth is increasing – Since the 20th century, temperature rose 0.6 – 0.9°C – Human activity (CO2 emissions and deforestation) is drastically increasing the concentration of greenhouse gases • Impacting Earth’s albedo © Cengage Learning 2016 (a) Satellite observations of ozone concentrations over Antarctica are shown here as red for highest concentration and violet for lowest. Since the 1970s, a hole in the ozone layer has developed over the South Pole. (b) Although ozone depletion is most dramatic above the South Pole, ozone concentrations have declined at all latitudes. © Cengage Learning 2016 Common Misconceptions • Misconception: The observed warming of Earth is result of natural causes rather than greenhouse effect – Truths: • Natural causes should be driving temperatures to decrease, not increase Common Misconceptions (cont’d.) • Misconception: All of Earth will warm at same rate – Truth: • N. America will be warm and dry while Europe becomes more wet and cool. • Sun’s luminosity has remained constant © Cengage Learning 2016 © Cengage Learning 2016 Test Your Learning? The greenhouse effect is caused mostly by a) pesticides b) depletion of the ozone layer c) carbon dioxide in the atmosphere d) strong magnetic field e) the aurora borealis © Cengage Learning 2016 http://hea-www.harvard.edu/~pgreen/ © Cengage Learning 2016 Campus.kellerisd.net 6 4/20/2017 21-1: The Moon: The View from Earth 21-1: The Moon From Earth, we always see the same side of the moon. Moon rotates around its axis in the same time that it takes to orbit around Earth: The side of the Moon that faces Earth is a familiar sight. Craters have been named for famous scientists and philosophers, and the so-called seas have been given romantic names. Mare Imbrium is the Sea of Rains, and Mare Tranquillitatis is the Sea of Tranquillity. There is, in fact, no water on the Moon. Tidal coupling: Earth’s gravitation has produced tidal bulges on the moon; Tidal forces have slowed rotation down to same period as orbital period © Cengage Learning 2016 © Cengage Learning 2016 21-1: Lunar Surface Features Two dramatically different kinds of terrain: 21-1: Impact Cratering (cont’d.) 1. A meteorite approaches the lunar surface at high velocity. 2. On impact, the meteorite is deformed, heated, and vaporized. • Highlands: Mountainous terrain, scarred by craters • Lowlands: ~ 3 km lower than highlands; smooth surfaces: 1 Maria (pl. of mare): Basins flooded by lava flows 2 © Cengage Learning 2016 © Cengage Learning 2016 21-1: Impact Cratering (cont’d.) 21-1:History of Impact Cratering Impact Cratering 3. The resulting explosion blasts out a round crater. 4. Slumping produces terraces in crater walls, and rebound can raise a central peak. Most of the craters on the Moon were produced long ago when the Solar System was filled with debris from planet building. As that debris was swept up, the cratering rate fell rapidly. 3 4 © Cengage Learning 2016 © Cengage Learning 2016 7 4/20/2017 © Cengage Astronomy Learning 2016 ClassAction: Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu) © Cengage Astronomy Learning 2016 ClassAction: Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu) 21-1: Missions to the Moon 21-1: Apollo Landing Sites (2) Major challenges: Need to carry enough fuel for: • in-flight corrections, • descent to surface, Selected to sample as wide a variety as possible of different lowland and highland terrains. • re-launch from the surface, • return trip to Earth; need to carry enough food and other life support for ~ 1 week for all astronauts on board. Lowland s (maria) Solution: • only land a small, light lunar module; • leave everything behind that is no longer needed. © Cengage Learning 2016 Highlands Lunar module (LM) of Apollo 12 on descent to the surface of the moon 21-1: The Apollo Missions (cont’d.) © Cengage Learning 2016 21-1: Lunar Geology • All lunar rocks are igneous (magma or lava) – No sedimentary (cementing of layers) rocks – Contain little water – Lunar maria composed of dark, dense basalts (fine grain volcanic rock) – Some basalts are vesicular (cavities) – Highlands have anathorsite rock (contains only one major mineral) – Highlands and lowlands are covered with regolith (dust, soil, broken rock) © Cengage Learning 2016 © Cengage Learning 2016 8 4/20/2017 21-1: Formation of Maria 21-1: Origin of Mare Imbrium Lava flooding after the end of the heavy bombardment filled a giant, multiringed basin and formed Mare Imbrium. 1.Four billion years ago, an impact forms a multiringed basin over 1000 km (600 mi) in diameter. 2.Continuing impacts crater the surface but do not erase the high walls of the multiringed basin. (a) Much of the near side of the Moon is marked by great, generally circular lava plains called maria. Major impacts broke the crust, and lava welled up to flood the largest, deepest basins, forming the maria. (b) The crust on the far side is thicker, and there is much less flooding. Even the huge Aitken Basin contains little lava flooding. In these maps, color marks elevation, with red the highest regions and purple the lowest. © Cengage Learning 2016 1 2 © Cengage Learning 2016 21-1: Origin of Mare Imbrium 21-1: Origin of Mare Imbrium 3. Impacts form a few large craters, and, starting about 3.8 billion years ago, lava floods low regions. 4. Repeated lava flows cover most of the inner rings and overflow the basin to merge with other flows. 5. Impacts continue, including those that formed the relatively young craters Copernicus and Kepler. 5 3 4 © Cengage Learning 2016 © Cengage Learning 2016 21-1: Formation of Moon: Giant Impact Theory Sometime before the Solar System was 50 million years old, a collision produced Earth and the Moon in its orbit inclined to Earth’s equator. 1.A protoplanet nearly the size of Earth differentiates to form an iron core. 3 2.Another body that has also formed an iron core strikes the larger body and merges, trapping most of the iron inside. 1 2 4 © Cengage Astronomy Learning 2016 ClassAction: Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu) 5 © Cengage Learning 2016 9 4/20/2017 21-1: Giant Impact Theory 4 - F: Giant Impact Theory 3. Iron-poor rock from the mantles of the two bodies forms a ring of debris. 4. Volatiles are lost to space as the particles in the ring begin to accrete into larger bodies. 5. Eventually the Moon forms from the iron-poor and volatile-poor matter in the disk. 5 3 4 © Cengage Learning 2016 © Cengage Learning 2016 Test Your Learning? There is very little atmosphere on the Moon because a) dry rocks on the Moon absorbed its own atmosphere b) it was blown away by meteor bombardment c) its low mass and high temperature allowed most gases to escape Acknowledgment • The slides in this lecture is for Tarleton: PHYS1411/PHYS1403 class use only • Images and text material have been borrowed from various sources with appropriate citations in the slides, including PowerPoint slides from Seeds/Backman text that has been adopted for class. d) the gravitational tidal forces from the Earth stripped © Cengage Learning 2016 it away http://hea-www.harvard.edu/~pgreen/ © Cengage Learning 2016 10