Juno: First Look at Jupiter’s North PoleCourse AnnouncementsAssignmentsModified Kepler’s LawsModified Kepler’s LawsUniv. of Colorado’s Online Orbit SimulatorChapter 3Light: Our source of informationLight and RadiationThe Nature of Light“Invisible” LightLight – It’s a wave (and particle)Anatomy of WavesAnatomy of a WaveAnatomy of a WaveThe Visible Light SpectrumFrequently used UnitsTravelling WavesElectric Forces and FieldsElectric Forces and FieldsElectricity and MagnetismElectromagnetic WavesDiscovery 3-1Electromagnetic (EM) WavesThe Electromagnetic (EM) SpectrumAtmospheric OpacityAtmospheric OpacityOrion Nebula – Multi-wavelengthThe Crab Nebula in multiple wavelengthsThermal RadiationJuno: First Look at Jupiter’s North PoleCredit: NASA/JPL-Caltech/SwRI/MSSSCourse Announcements•Five extra credit opportunities this week–For observations, report to the roof of the this building–BE ON TIME!•Quiz 2 will take place Monday, 19 September•Exam 1 will not take place on Wednesday, 21 September–Exact exam date TBD, but likely to be 28 Sept.•Attendance: Based on last Friday’s Notecard Question, attendance was at 47%. This is not acceptable, and if another instance of below 50% occurs, the following quiz will be a pop-quiz.AssignmentsReading Assignments•Chapter 3. Sections 3.4 – 3.5[Read for Wednesday, 14 Sept.]Parallel Lectures•No new parallel lecturesMastering Astronomy•Chapter 2 Homework[Due Tuesday, 13 Sept. at 11:59 PM EDT]Modified Kepler’s LawsFor our Solar System, the center of mass is in the Sun, but not at the center of the Sun. The Sun orbits the common center of mass of all the planets!Sun and planet orbit a common focusModified Kepler’s LawsWith a bit of mathematical manipulation of Newtonian Gravity applied to Kepler’s 3rd Law.Newton’s Modification to Kepler’s 3rd LawWith Newton’s modification, we can now apply Kepler’s 3rd Law to any system! (Earth – Moon; Extrasolar Planets; etc.)Univ. of Colorado’s Online Orbit SimulatorPhET – My Solar System•Fun module for you to play with to reinforce Kepler’s Modified Three Laws.•Bonus: The field of study that understands the motions of things in the Universe is called celestial mechanics, and it is what NASA scientists and engineers must use to calculate trajectories of spacecraft and when is the right time to launch.CHAPTER 3Radiation - LightVisible Light + Radio WavesCredit: HST/VLALight: Our source of information•Looking through time and space•Most of universe inaccessible except for its light•Light, a form of radiation, carries a wealth of information to usAlmost everything we know about the universe outside of the Solar System, we know through studying its light50,000 light-yearsChemical composition, ages, state of motion, temperature, density, structure, …Light and Radiation•Radiation is any way in which energy is transmitted through space from one point to another without the need for a physical connection between the two locations•Electromagnetic radiation, or light, is radiation caused by rapid variations in electric and magnetic fields•What humans can see is called visible light–However, visible light, is just a tiny portion of all the kinds of light that existElectromagnetic RadiationThe Nature of LightWell, that got weird quickly!•Light is electromagnetic radiation–electric and magnetic field components•Light is both a wave and a particle–Here we discuss the wave nature of light.•Light is much more than what human’s see (visible light)•All forms of light (red light, green light, infrared light, X-ray light, etc.) travel at the same speed: the speed of light“Invisible” LightOther forms of light/electromagnetic radiationRadio waves, Microwaves, Infrared Light, Ultra Violet Light, X-rays, and Gamma Rays- All of which are invisible to the human eyeHuman eye only capable of seeing Visible LightBelow is an example of Infrared Light Interested in human perception of color. Check out this RadiolabCredit:NASA/IPACVisible InfraredLight – It’s a wave (and particle)Wave Motion – Ripples on a PondThe water just moves up and down The wave travels across the surface transmitting energy, and therefore, carrying informationUC Boulder PhET – Wave SimulatorAnatomy of WavesAll waves, including electromagnetic waves (light)Wave Motion transmits energy/information without the physical transport of materialAnatomy of a WaveThe time elements: Frequency and PeriodFrequency is the number of crests that pass a given point per second.The Period is the time it takes the wave to travel from crest-to-crestFrequency = 1/Period [unit: 1/seconds or Hertz]Note that this is an inversely proportional relationshipAnatomy of a WaveSpace Characteristics: WavelengthThe wavelength is the crest-to-crest, or equivalently, trough-to-trough, distance.The amplitude is how high (or low) a wave can get above (or below), it’s undisturbed state.The velocity of a wave is the speed at which it travels, i.e., velocity = wavelength/period, or equivalently, Wave velocity = wavelength x frequency [Distance per time]The Visible Light SpectrumSpectrum (plural: Spectra) is dividing up the light to into its wavelengths (equivalently frequencies)Larger Wavelengths(usually said as LONGER wavelengths, or“Redder” Wavelengths)Lower FrequenciesSmaller Wavelengths(Shorter Wavelengths, or Bluer Wavelengths)Higher FrequenciesThe Visible SpectrumFrequently used UnitsI have a wavelength biasThe nanometer (nm) is frequently used for wavelength - nano is the prefix for 10-9, so 1 nm = 1.0 x 10-9 m. (1 billion nanometers in 1 meter)The micrometer (µm), or micron, is also frequently used - micro is 10-6 or 1 millionth. 1 µm = 1000 nmSometimes astronomers use the Ångstrom (1 Å = 10-10 m = 0.1 nm)Green Light~ 550 nm0.55 µm5500 ÅRed Light~700 nm0.7 µm7000 ÅViolet Light~400 nm, or0.4 µm4000 ÅTravelling Waves•Water waves, sound waves, etc., travel in a medium (e.g., water, air), so what do light waves travel in?•Electromagnetic waves require no medium!•Created by accelerating charged particles–E.g., protons (positive charge) and electrons (negative charge)No “Luminiferous Aether” requiredElectric Forces and Fields•Analogous to gravitational force, all charged particles (electrons, protons, etc.) exert and electric force•Unlike gravity, the electric force can be both attractive and repulsiveNo “Luminiferous Aether” requiredLike charges
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