Astronomy 101 The Solar System Tuesday, Thursday 2:30-3:45 pm Hasbrouck 20 Tom Burbine [email protected] HoursHomeworkAstronomy InformationFinalHW #5HW #6HW #7Atoms make up moleculesSlide 11Slide 12SpectroscopySlide 14Water on the MoonDefinitionsLight cause water molecules to vibrateHow much water?How do you use light to determine what is in an astronomical body like a star?Slide 20What happens when electrons absorb energy?Slide 22Slide 23eVRulesSlide 26Slide 27Types of spectraSlide 29So why is this importantSoEmission line spectraHow can you determine velocities of objects?Slide 34Slide 35nanometerFormulas for lightBlackbodySlide 39Slide 40Any Questions?Astronomy 101The Solar SystemTuesday, Thursday2:30-3:45 pmHasbrouck 20Tom [email protected]•Course Website:–http://blogs.umass.edu/astron101-tburbine/•Textbook:–Pathways to Astronomy (2nd Edition) by Stephen Schneider and Thomas Arny.•You also will need a calculator.Office Hours•Mine•Tuesday, Thursday - 1:15-2:15pm•Lederle Graduate Research Tower C 632•Neil•Tuesday, Thursday - 11 am-noon •Lederle Graduate Research Tower B 619-OHomework•We will use Spark•https://spark.oit.umass.edu/webct/logonDisplay.dowebct•Homework will be due approximately twice a weekAstronomy Information•Astronomy Help Desk•Mon-Thurs 7-9pm•Hasbrouck 205•The Observatory should be open on clear Thursdays •Students should check the observatory website at: http://www.astro.umass.edu/~orchardhill for updated information•There's a map to the observatory on the website.Final•Monday 12/14 •4:00 pm•Hasbrouck 20HW #5•There is a HW #5 replace which will replace your HW #5 score if you get a higher gradeF = G M1 M2 r2 G = 6.67 x 10-11 m3/(kgs2)HW #6 •Due todayHW #7•Due next ThursdayAtoms make up molecules•H2O - water•CO2 – carbon dioxide•CH4 - methaneSpectroscopy•Spectroscopy is the study of the interaction between radiation and matter as a function of wavelength (λ ).•You can use spectroscopy to determine what is in a body (planet, star, etc.) or atmospherehttp://upload.wikimedia.org/wikipedia/commons/f/f5/Light_dispersion_conceptual_waves.gif•How did scientists recently determine that there was water on the Moon?Water on the Moonhttp://www.nasa.gov/images/content/388950main_ROGER_2-516.jpgWhite line - NASA' Cassini spacecraft Blue line - NASA's Moon Mineralogy Mapper instrument on the Indian Chandrayaan-1 spacecraftGrey - H2O and OH absorptionsDefinitions•Reflectance – How much light an object reflects•Absorption – Light is absorbed and not reflectedLight cause water molecules to vibrate•http://www.btinternet.com/~martin.chaplin/vibrat.htmlHow much water?•If you had a cubic meter of lunar soil, you could squeeze it and get out a liter of water•Water has to be near the surfaceHow do you use light to determine what is in an astronomical body like a star?•http://www.youtube.com/watch?v=9LrTeadnF6Q•http://www.youtube.com/watch?v=VY-bcMfLKegWhat happens when electrons absorb energy?http://www.meditech.cn/images/pic9.jpghttp://library.thinkquest.org/C006669/media/Chem/img/bohr.gifEnergy levels where an electron can resideTo go to a higher energy level, an electron needs to gain energyTo go to a lower energy level, an electron needs to lose energyeV•1 eV = 1.6 x 10-19 JoulesRules•An electron can not jump to a higher energy level unless it gains energy from somewhere else–Absorbs a photon–Gains kinetic energy from an impacting particle•To go to a lower energy level, the electron must lose energy–Emits a photon•Electron jumps can occur only with the particular amounts of energy representing differences between possible energy levelsHeated hydrogen gasEmission line spectrumWhite light through cool hydrogen gasAbsorption line spectrumTypes of spectra•Emission – radiation is emitted at characteristic wavelengths–Material is “hot” so electrons keep on bumping into each other and transferring kinetic energy to each other so they jump between particular energy levels•Absorption – radiation is absorbed at characteristic wavelengths–Radiation passes through the materialhttp://www.astro.bas.bg/~petrov/herter00_files/lec07_04.jpgSo why is this important•Different elements have different number of electrons•Different elements have different energy levels for their electronsSo•Different elements can absorb light at specific energies•Different elements can emit light at specific energies•So if you can measure the wavelength of the light from an astronomical body, you can determine whats in itEmission line spectraHow can you determine velocities of objects?•Doppler Shift – The wavelength of light changes as the source moves towards or away from you•Since you know the wavelength position of emission or absorption features •If the positions of the features move in wavelength position, you know the source is movingSo•Source moving towards you, wavelength decreases–blueshift•Source moving away from you, wavelength increases–redshift•http://www.youtube.com/watch?v=-t63xYSgmKE•http://www.youtube.com/watch?v=a3RfULw7aAYnanometer•1 nanometer = 1 x 10-9 metersFormulas for light•vrad/c = λshift – λrest λrest•Rest wavelength of a line of hydrogen is at 656.285 nm•You observe this line at 656.255 nm for a star•What is the velocity of this star?•vrad/c = (656.255 -656.285)/656.285 nm•vrad/c = -4.5712 x 10-5•vrad = -4.5712 x 10-5 *3 x 108 m/s = -13,700 m/s = -13.7 km/s•It is blue-shifted so the motion is toward usBlackbody•A black body is an object that absorbs all electromagnetic radiation that falls onto it. •Perfect emitter of radiation•Radiates energy at every wavelengthhttp://www.daviddarling.info/images/blackbody.jpg•Stefan-Boltzman Law - energy radiated per unit surface area of a black body in unit time is directly proportional to the fourth power of the black body’s temperature•Wien’s Law - blackbody curve at any temperature has essentially the same shape as the curve at any other temperature, except that each wavelength is displaced, or moved over, on the graph•Stars and planets act can be modeled as blackbodieshttp://www.astro.ncu.edu.tw/contents/faculty/wp_chen/Ast101/blackbody_curves.jpgAny
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