Astro 301/ Fall 2006(50405)Introduction to Astronomyhttp://www.as.utexas.edu/~sj/a301-fa06Instructor: Professor Shardha JogeeTAs: Biqing For, Candace Gray, Irina MarinovaLecture 13 Tu Oct 17Announcements- Exam 1 : Well done! A=40% B=30% C=18% D=7% F=5% - Homework 2 given back today. Solution set posted outside lecture hallQ1 : Candace Q2: Irina Q3: Bi-Qing - Quiz 3 next Tuesday: Everything since quiz 2.-- Light as electromagnetic waves (continuned)- Processing light as electromagnetic waves - Optical light and optical color-- Unveiling the properties of stars from their light (continuum emission)- Luminosity versus Flux- Spectrum of an object: continuum emission, absorption lines, emission lines- Kirchhoff’s first law- Wien’s law: relating surface temperature and wavelength of maximum emission - The temperatures of stars - Stefan Boltzmann’s law : relating surface temperature and surface flux of a star- The luminosity function of stars - The Hertzsprung-Russell diagram.- Types of stars- The norms and extremes of stellar radii and densities.Recent and upcoming topics in classDispersing while light into its constituent optical EM wavesViolet, Blue, Green, Yellow, Orange Red Processing light as electromagnetic wavesProcessing light as electromagnetic waves Emission, Transmission, Absorption, ReflectionOptical light and optical colorType of EM wave Typical wavelength--------------------------------------------------------------------------------------------------------------------------------------Gamma rays 10-16m X rays 10-12m Ultraviolet 3 x 10-7m Optical 4 to 9 x 10-7m = Violet, blue, green, yellow, orange, redInfrared 10-6m to 10-4m Radio 10-3m to 10 m A body emits light across a large range of the EM spectrum: infrared, optical, UV, etc But human eye is sensitive to the optical (visible) part of the EM spectrumConcept of ‘color’ of an objectHow to Hold the Prism to See a SpectrumHold the prism point down, below eye level.blackboardBlackboard lightwhite lightX-ray/ROSATUltraviolet/ASTR0-1 Visible lightNear infrared/SpitzerRadio 21cm/VLAWhy does the same galaxy (M81) look so different when we look at the light it emits at different wavelengths (from X-ray to visible to radio)? What information does light from distant stars/galaxies carry?1. See in –class notes: difference between flux and luminosityflux depends inversely on the square of the distance.2. Demo : Which object has a higher luminosity?Luminosity versus Flux of an objectWhat information does light from distant stars/galaxies carry? Pleiades stellar cluster M80 globular cluster (HST image)What does the light from a star tell us about the properties of the star?(temperature, radius, luminosity of the star)1) A spectrum is a plot of the intensity of light at each wavelength.When the total flux from an object is separated into the flux at different wavelengthsand the intensity of the flux is plotted against wavelength, we get a spectrum for that object. 2) In general a spectrum can have 3 types of features: continuum emission : emission over a continuous range of wavelengthsemission lines : emission above the continuum at specific wavelengths absorption lines: lack of emission (dip below the continuum) at specific wavelengths A SpectrumAmazingly, the continuum ermission , emission lines, absorption lines. in the spectrum of an object can reveal to us its temperature the total flux at its surface its chemical composition, (like a DNA genetic code) its recession speed, its distanceInformation in a
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