ASTR 1120General Astronomy:Stars & Galaxies!NNOUNCEMENTS:- First homework on Mastering Astronomy: due Thursday, 09/10, by 5pm (late penalty)- Math review session Thursday 09/03: 5-7pm in Ramaley Biology, RAMY N1B23- First observing session at Fiske TOMORROW Light: The Cosmic MessengerL I G H T• For nearly all astronomical objects, light brings us ouronly information• Need to understand what light is and how it can beinterpretedLight is a form of !NERG"• White light is made up of many differentcolorsFour Ways in Which Light canInteract with Matter1. Emission – matter releasesenergy as light2. Absorption – matter takesenergy from light3. Transmission – matterallows light to pass through it4. Reflection – matter repelslight in another directionFour Ways in Which Light canInteract with Matter1. Emission – matterreleases energy as light2. Absorption – mattertakes energy from light3. Transmission – matterallows light to passthrough it4. Reflection – matterrepels light in anotherdirectionFour Ways in Which Light canInteract with Matter1. Emission – matterreleases energy as light2. Absorption – mattertakes energy from light3. Transmission – matterallows light to passthrough it4. Reflection – matterrepels light in anotherdirectionFour Ways in Which Light canInteract with Matter1. Emission – matterreleases energy as light2. Absorption – mattertakes energy from light3. Transmission – matterallows light to passthrough it4. Reflection – matterrepels light in anotherdirectionWhy is a rose red?A. The rose emits red light.B. The rose absorbs red light.C. The rose transmits red light.D. The rose reflects red light.Clicker QuestionWhy is a rose red?A. The rose emits red light.B. The rose absorbs red light.C. The rose transmits red light.D. The rose reflects red light.Clicker QuestionWave-Particle Duality of Light• Light can behave like a wave– Frequency, wavelength, amplitude• Light can also behave like a particle– Photons, discrete amounts of energy =“quanta”= AMPLITUDEAnatomy of a Wave• Speed of light isthe SAME for allwavelengths• The shorter thewavelength, themore cycles passper second– Train analogy…• How to rememberequation?– Unit Analysis!Light asa WAVELight as a PARTICLE• Light can also be thought of as a particle ! “photon”NOT proton! A photon is a mass-less particle ofelectromagnetic radiation energyWave-particle duality seen in otherparticles (e.g., electrons) as wellPhoton Energy Depends onFrequency/and ?E ! fE ! 1 / !Photon Energy Depends onFrequency/WavelengthE ! fE ! 1 /What is LIGHT?A. Light is a wave, like sound only much faster.B. Light is like little particles. Each one is aphoton.C. Light is the absence of dark.D. A kind of energy we model with some of theproperties of waves and some properties ofparticles.E. Light is the sensation you feel when hit byenergy, visible or invisible.Clicker QuestionWhat is LIGHT?A. Light is a wave, like sound only much faster.B. Light is like little particles. Each one is aphoton.C. Light is the absence of dark.D. A kind of energy we model with some of theproperties of waves and some properties ofparticles.E. Light is the sensation you feel when hit byenergy, visible or invisible.Clicker QuestionWhen compared to RED light (! = 700 nm),Blue light (! = 400 nm) is:A. Longer wavelengthB. Lower FrequencyC. Higher energy photonsD. Faster photonsE. None of the aboveClicker QuestionWhen compared to RED light (! = 700 nm),Blue light (! = 400 nm) is:A. Longer wavelengthB. Lower FrequencyC. Higher energy photonsD. Faster photonsE. None of the aboveClicker QuestionThe Electromagnetic SpectrumLight as Information Bearer By studying the spectrum of an object, we can learn its:• Composition• Temperature• VelocityWe can separate light into its different wavelengths (spectrum).Matter: a Material World• ATOM: nucleus made of protons and neutronsA cloud made of electrons surrounds the nucleusElectrons are held onto the atom by electric force. Electrons havenegative electric charge, protons are positive. Neutrons areneutral.Electrically neutral atoms have the same number of protons andelectronsBut first we need a review of…Atoms Involve Big Empty SpacesPeriodic Table of the ElementsAtomic Number = # of protons in nucleusAtomic Mass Number = # of protons + neutronsHydrogen: simplest andmost commonHelium• Mostly an atom will have a certain “normal”number of neutrons along with the protons.• But occasionally, an atom will have a fewmore or less neutrons than normal. This iscalled an isotope of that element.The number of protons (!"#$%&'()$*+,!""#$%&%#'(&)*(+"%"#(&'%),"#$(-)#%."(.(-(,'/Carbon IsotopesDeuterium is an isotope of Hydrogen.Which of the following makes sensefor the composition of Deuterium?A. 1 proton, 0 neutrons, 1 electronB. 2 protons, 0 neutrons, 2 electronsC. 2 protons, 2 neutrons, 2 electronsD. 1 proton, 1 neutron, 1 electronE. 1 proton, 0 neutrons, 0 electronsClicker QuestionDeuterium is an isotope of Hydrogen.Which of the following makes sensefor the composition of Deuterium?A. 1 proton, 0 neutrons, 1 electronB. 2 protons, 0 neutrons, 2 electronsC. 2 protons, 2 neutrons, 2 electronsD. 1 proton, 1 neutron, 1 electronE. 1 proton, 0 neutrons, 0 electronsClicker Questionp+atomic number = 1atomic mass number = 1What if an electron is missing?ionH+1What if two or more atoms combine toform a particle?p+p+8p+8nmoleculeH2O
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