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Astronomy/Geology 110 Tuesday, Thursday 2:40-4:00 pm Carnegie 204 Tom Burbine email@example.com Course • Course Website: – http://abacus.bates.edu/~tburbine/ATGE110/ – Also on Lyceum.bates.edu • Textbook: – Moon and Planets (5th Edition) by William K. Hartmann • You also will need a calculator. Office Hours • Tuesday 1:30-2:30 pm • Thursday 11 am-noon • Carnegie 204 • I will also be having lunch at the Commons every Thursday from noon-1 pm Help Sessions • Monday and Wednesdays at 4 pm in Carnegie 215 Quiz Average • Quiz Average was an 86 • Grades ranged from a 52 to a 100 HW #4 (due today) • Choose a planetary science book to read • Submit the title of the book and the author • Write a short paragraph on why you chose this book • You will give a book report during one of your last two lab periods on the book HW #5 (due Thursday) • Energy problems HW #6 (due September 25) • You need to interview and film a number of people and ask them a planetary science question that they should know the answer. The video should be about a minute long. The end of the video should include the answer. • Make a video as a team of two or three (or by yourself if you don't want a partner). • Cameras can be obtained at the Digital Media Center 121 Pettigrew. • Macs are available at the Digital Media Center for editing the video and burning the video to a disk. • Submit the file to me on September 25. The file should have your names or name in the title. HW #7 (due next Tuesday) • Star problems A Maybe Planet, Orbiting Its Maybe Sun 7 to 12 times as massive as Jupiter star is 85% as massive as the Sun, but less than 0.1% its age near-infrared image http://www.nytimes.com/2008/09/18/science/space/18planet.html 5 th Dwarf Planet • 5th dwarf planet Haumea and its two moons Hi'iaka and Namaka, • Named after the Hawaiian fertility goddess • Moons after the patron goddess of Hawaii and a water spirit. http://en.wikipedia.org/wiki/Image:2003EL61art.jpg 1/3 the mass of Pluto Matter • Matter is material Energy • Energy is what makes matter move • In English Units, we use calories to measure energy • In science (and in this class), we will use joules to measure energy 3 basic categories of energy • Kinetic energy – energy of motion • Potential energy – energy being stored for possible conversion into kinetic energy • Radiative energy – energy carried by light Kinetic energy • Kinetic energy = ½ mv2 • m is mass in kg • v is velocity in meters/s • A joule has units of kg-m2/s2 • How much energy does a 2 kg rock have if it is thrown at 20 m/s? • Kinetic energy = ½ mv2 • A) 200 J • B) 400 J • C) 40 J • D) 800 J Answer • KE = ½ * 2 * (20) *(20) = 400 joules Thermal energy • Temperature – average kinetic energy of particles • Higher temperature – more kinetic energy, particles moving faster • For examples, air molecules around you are moving at ~500 m/s Temperature scales • In America, we use Fahrenheit • Water freezes at 32 degrees F • Water boils at 212 degrees F • Everywhere else, they use Celsius • Water freezes at 0 degrees C • Water boils at 100 degrees C In Science • Temperature is measured in Kelvin • Zero Kelvin is absolute zero – nothing moves • Add 273.15 to the Celsius temperature to get the Kelvin temperature • 273.15 Kelvin = 0 degrees Celsius Gravitational Potential Energy • Gravitational Potential Energy released as an object falls depends on its mass, the strength of gravity, and the distance it falls • For example, your gravitational potential energy increases as you go farther up in the air • This is because you hit the ground at a faster speed if you jump from a higher distance Converting Mass to Energy • What is the most famous formula in the world? E = mc2 • m is mass in kilograms • c is speed of light in meters/s • So E is in joules • very small amounts of mass may be converted into a very large amount of energy and Who came up with it? • How much energy can be produced if you can convert 10 kg of material in energy? • E = mc2 • A) 3.0 x 108 J • B) 3.0 x 1016 J • C) 9.0 x 1017 J • D) 9.0 x 1010 J Answer • E = 10 kg * (3 x 108 m/s) * (3 x 108 m/s) • E = 10* (9 x 1016) J • E = 90 x 1016 J • E = 9.0 x 1017 J Mass-Energy • So Mass is a form of potential energy • Where is one place where you see mass converted into energy? Atoms • Atoms are made up of 3 types of particles • Protons – positive charge (+1) • Electrons – negative charge (-1) • Neutrons – neutral charge (no charge) • Protons and Neutrons are found in the nucleus Elements • Different elements have different numbers of protons • The properties of an atom are a function of the electrical charge of its nucleus Charge • If an atom has the same number of electrons and protons, it has a neutral charge • More electrons than protons, negatively charged • More protons than electrons, positive charged • Neutrons have neutral charge so don’t affect the charge of an atom Definitions • Atomic Number – Number of protons • Atomic Mass – Number of protons and neutrons • U235 – atomic mass 92- atomic number • usually 92 not written • Isotopes – Same number of protons but different numbers of neutrons First nuclear weapons • Worked by nuclear fission • Use Uranium-235 • If a free neutron runs into a U-235 nucleus, the nucleus will absorb the neutron without hesitation, become unstable and split immediately • The energy released by a single fission is due to the fact that the fission products and the neutrons, together, weigh less than the original U-235 atom Atoms make up molecules • H2O • CO2 • CH4 • Atoms made up with 2 or more different atoms are called compounds Star Formation • How do we know that stars are continually forming? Age of Solar System versus the Universe • Solar System has an age of ~4.6 billion years • Universe has an age of ~13.7 billion years • All stars did not form at the beginning Astrophysical Analyses of the ages of Stars • The Sun has an estimated lifetime of ~10 billion years • Some stars have estimated lifetimes of ~10 million years Discovery of apparent star-forming regions • Discovery of regions where stars surrounded by clouds of hydrogen gas and dust Eagle Nebula (“Pillars of Creation”) young open cluster of stars region of hydrogen gas and dust The tower is 9.5 light-years high, about twice the distance from our Sun to the next nearest star. Hubble image http://en.wikipedia.org/wiki/Image:Eagle_nebula_pillars.jpg Molecular Cloud • A star-forming cloud is called a molecular cloud because low temperatures allow Hydrogen to form Hydrogen molecules (H2) • Temperatures like 10-30 K • Denser than surrounding regions • The clouds can reach tens of light years in diameter and have an average density of 10²–10³ particles per cubic centimeter – The average density in the vacuum of space in our solar system is one particle per cubic centimeter Triggered Star Formation • In triggered star formation, one of several events (e.g., supernova explosion) might occur to compress a molecular cloud and initiate its gravitational collapse. • As a region gets denser, its gravity gets higher • http://coolcosmos.ipac.caltech.edu/resources/infor mal_education/movies/SNR-VGA.mov Or • A region might be dense enough to collapse on its own Condensing • Molecular clouds tends to be lumpy • These lumps tend to condense into stars • That is why stars tend to be found in clusters Protostar • The dense cloud fragment gets hotter as it contracts • The cloud becomes denser and radiation cannot escape • The thermal pressure and gas temperature start to rise and rise • The dense cloud fragment becomes a protostar When does a protostar become a star • When the core temperatures reaches 10 million K, hydrogen fusion can start occurring Things you need to know • Fusion rate increases with increasing temperature • There is a relation between thermal pressure and gravity Classification of Stars • Stars are classified according to luminosity and surface temperature • Luminosity is the amount of power it radiates into space • Surface temperature is the temperature of the surface Luminosity-Distance Formula • Apparent brightness = Luminosity 4 x (distance)2 Usually use units of Solar Luminosity LSun = 3.8 x 1026 Watts Measuring Distance to Stars • Measuring distances to stars is much harder to measure than brightness • But to determine the Luminosity of the star, we need to know the distance to it Wien’s Law • Inverse relationship between the wavelength of the peak of the emission of a black body and its temperature • λ = 0.00290/T • λ is in meters • T is in Kelvin One nanometer = 1 x 10-9 m Surface Temperature • Determine surface temperature by determining the wavelength where a star emits the maximum amount of radiation • Surface temperature does not vary according to distance so easier to measure 1913 Who were these people? • These were the women (called computers) who recorded, classified, and catalogued stellar spectra • Willamina Fleming (1857-1911) classified stellar spectra according to the strength of their hydrogen lines • Classified over 10,000 stars Fleming’s classification • A - strongest hydrogen emission lines • B - slighter weaker emission lines • C, D, E, … L, M, N • O - weakest hydrogen lines emission lines Annie Jump Cannon (1863-1941) • Cannon reordered the classification sequence by temperature and tossed out most of the classes • She devised OBAFGKM More information • Each spectral type had 10 subclasses • e.g., A0, A1, A2, … A9 in the order from the hottest to the coolest • Cannon classified over 400,000 stars OBAFGKM • Oh Be A Fine Girl/Gal Kiss Me • Play song • http://www.mtholyoke.edu/courses/tburbine/AST R223/OBAFGKM.mp3 Cecilia Payne-Gaposchkin (1900-1979) • Payne argued that the great variation in stellar absorption lines was due to differing amounts of ionization (due to differing temperatures), not different abundances of elements Cecilia Payne-Gaposchkin (1900-1979) • She proposed that most stars were made up of Hydrogen and Helium • Her 1925 PhD Harvard thesis on these topics was voted best Astronomy thesis of the 20th century Hertzsprung-Russell Diagram • Both plotted spectral type (temperature) versus stellar luminosity • Saw trends in the plots • Did not plot randomly Remember • Temperature on x-axis (vertical) does from higher to lower temperature • O – hottest • M - coldest Hertzsprung-Russell Diagram • Most stars fall along the main sequence • Stars at the top above the main sequence are called Supergiants • Stars between the Supergiants and main sequence are called Giants • Stars below the Main Sequence are called White Dwarfs wd white dwarfs Classifications • Sun is a G2 V • Betelgeuse is a M2 I Radius • Smallest stars on the main sequence fall on the bottom right • Largest stars on main sequence fall on the top left • At the same size, hotter stars are more luminous than cooler ones • At the same temperature, larger stars are more luminous than smaller ones Main Sequence Stars • Fuse Hydrogen into Helium for energy • On main sequence, mass tends to decrease with decreasing temperature • Two fusion reactions; – Proton-proton dominates – Sun’s mass or less – CNO cycle dominates – More massive than Sun • http://www.astronomynotes.com/starsun/s3.htm • http://www.astro.ubc.ca/~scharein/a311/Sim/fusio n/Fusion.html Positron-positively charged electron 2 protons fuse together Forms proton and neutron (deuterium- Hydrogen isotope) Positron given off and destroyed by colliding with electron 2 gamma rays given off Figure 15.7 Neutrino given off proton fuses with deuterium Forms Helium-3 Gamma ray given off Figure 15.7 Collision of two Helium-3 nucleus Produces Helium-4 nucleus and 2 protons Steps 1 and 2 must occur twice Figure 15.7 Proton-Proton Chain Reaction • Takes an average of 109 years to complete at the temperature of the Sun’s core – A hydrogen nucleus waits on the average 1 billion years before it undergoes an interaction with another hydrogen nucleus to initiate the sequence • It if occurred faster, Sun would run out of fuel Neutrinos • Neutrinos (ν) – almost massless particles • No charge • Originally postulated to preserve conservation of energy, conservation of momentum, and conservation of angular momentum in beta decay (neutron decays into a proton) energy + p+ → n0 + e+ + νe • It takes a neutrino about 2 seconds to exit the Sun • More than 50 trillion solar electron neutrinos pass through the human body every second CNO cycle www.nobelprize.org What was the solar neutrino problem? • A) More neutrinos appeared to be produced from the Sun than expected from models • B) Less neutrinos appeared to be produced from the Sun than expected from models • C) Neutrinos are dangerous to humans • D) Neutrinos interfere with the fusion of hydrogen into helium • E) Neutrinos turn helium into Lithium What is the solar neutrino problem? • A) More neutrinos appear to be produced from the Sun than expected from models • B) Less neutrinos appear to be produced from the Sun than expected from models • C) Neutrinos are dangerous to humans • D) Neutrinos interfere with the fusion of hydrogen into helium • E) Neutrinos turn Helium into Lithium How was the Homestake Gold Mine used to detect neutrinos? • A 400,000 liter vat of chlorine-containing cleaning fluid was placed in the Homestake gold mine • Every so often Chlorine would capture a neutrino and turn into radioactive argon • Modelers predict 1 reaction per day • Experiments found 1 reaction every 3 days How was the problem solved? • Neutrinos can change from the type that had been expected to be produced in the sun's interior into two types that would not be caught by the detectors in use at the time. • How much longer will it take the Sun to use up all its “fuel”? • When the Sun uses up its fuel it will start expanding, which will be bad for people living on Earth Things you need to know • Energy source for sun is four hydrogen atoms combining to produce one helium atom • about 0.7% of the original mass is turned into energy during this process • 10% of the Sun’s mass is hot (~8 million Kelvin or above) enough to undergo fusion • Mass of the Sun = 2 x 1030 kg And • Total lifetime = (energy available) (rate [energy/time] at which sun emits energy) • rate [energy/time] at which the Sun emits energy is equal to 3.8 x 1026 Watts (Joules/second) And • Time left = Lifetime – current age • Current age = ~5 billion years Calculation • Mass of the Sun that is turned into energy • m = 2 x 1030 kg * 10% * 0.7% • m = 1.4 x 1027 kg of Sun can be turned into energy • E = mc2 • E = 1.4 x 1027 kg times 9 x 1016 m2/s2 • E = 1.26 x 1044 Joules Calculation • Lifetime = 1.26 x 1044 Joules/3.8 x 1026 Joules/second • Lifetime = 3.3 x 1017 seconds • Lifetime = 1.05 x 1010 years • Time left = 10.5 billion years – 5 billion years • Time left = 5.5 billion years Fusion • The rate of nuclear fusion is a function of temperature • Hotter temperature – higher fusion rate • Lower temperature – lower fusion rate • If the Sun gets hotter or colder, it may not be good for life on Earth What is happening to the amount of Helium in the Sun? • A) Its increasing • B) its decreasing • C) Its staying the same What is happening to the amount of Helium in the Sun? • A) Its increasing • B) its decreasing • C) Its staying the same So how does the Sun stay relatively constant in Luminosity (power output) Figure 15.8 Figure 15.4 Parts of Sun Core • Core – 15 million Kelvin – where fusion occurs Figure 15.4 Radiation zone • Radiation zone – region where energy is transported primarily by radiative diffusion • Radiative diffusion is the slow, outward migration of photons Figure 15.13 Photons emitted from Fusion reactions • Photons are originally gamma rays • Tend to lose energy as they bounce around • Photons emitted by surface tend to be visible photons • Takes about a million years for the energy produced by fusion to reach the surface Figure 15.4 Convection Zone • Temperature is about 2 million Kelvin • Photons tend to be absorbed by the solar plasma • Plasma is a gas of ions and electrons • Hotter plasma tends to rise • Cooler plasma tends to sink Figure 15.14 Granulation – bubbling pattern due to convection bright – hot gas, dark – cool gas Figure 15.14 Figure 15.10 Figure 15.4 Photosphere • Photosphere is the solar surface • Where photons escape into space Sunspots • Sunspots are on the photosphere • Have temperatures of ~4,000 K • Photosphere is 5,800 K Sunspots • Sunspots are regions of intense magnetic activity • Charged particles tend to follow magnetic field lines Figure 15.17 Sunspot Cycle Figure 15.21 The cycle has a period of approximately 11 years, but the interval between maxima can be as short as 7 years and as long as 15 years. Maunder Minimum • Between 1645 and 1715, the sunspot activity virtually stopped • Identified by E. W. Maunder from historical sunspot records Figure 15.4 Atmosphere of the Sun • Chromosphere – above the photosphere and below the corona • Temperature is about 10,000 Kelvin • Most of the Sun’s ultraviolet light is emitted from this region See Corona during eclipse Atmosphere of the Sun • Corona – tenuous uppermost layer of the Sun’s atmosphere • Temperature is about 1 million Kelvin • Most of the Sun’s X-rays are emitted from this region Corona • Extends millions of kilometers into space • Why its so hot is unknown • Sun's corona is constantly being lost as solar wind. Any Questions?
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