Pillars of Creation in Vis and Infrared Course Announcements Quiz 2 will take place Monday 19 September A few hints today Exam 1 will not take place on Wednesday 21 September Exact exam date TBD but likely to be 28 Sept Assignments Reading Assignments Chapter 4 Sections 4 1 4 3 Read for Friday 16 Sept Parallel Lectures No new parallel lectures Mastering Astronomy Chapter 3 Homework Due Monday 19 Sept at 11 59 PM EDT Quiz 2 Hints Guaranteed Questions One Force of Gravity Question Change the distance and or masses how does the force of gravity change One Kepler s 3rd Law Question I will give you either the semimajor axis or period and you must determine the other You may want to bring a calculator Example of okay answer with you showing your work Given P 7 years you eventually determine that the semimajor axis distance Must include unit for full credit Quiz 2 Hints Know the definitions for wavelength and frequency of a wave Know the pieces of the electromagnetic spectrum in order from longest to shortest or shortest to longest wavelength from Reading Know the four telescopic observations Galileo made that helped to overturn Geocentrism There will be one question concerning Seasons from Chapter 1 The Electromagnetic EM Spectrum Most of the universe is invisible to us Visible portion of EM Spectrum very small Note Scale is logarithmic i e each labeled tick mark is 10 times the previous Streteched out to a linear scale this graphic would stretch many light years in size You need to know the names of the pieces of the EM Spectrum in the correct order The Electromagnetic Spectrum The named sub spectra Know these in order Longer Wavelengths Radio waves Microwaves Infrared Visible Shorter Wavelengths Ultraviolet X rays Gamma Rays Atmospheric Opacity No one likes a sunburn Visible Window Spectral Windows Radio Window Absorbed by atmosphere Reaches Ground Absorbed by atmosphere Credit NASA Reaches Ground Atmospheric Opacity Spectral Windows The spectral windows are the wavelengths of the EM Spectrum that reach the ground Determines what light of the universe we can see from Earth s surface The universe looks very different depending on what wavelength color of light you are observing it in Credit NASA Orion Nebula Multi wavelength The Crab Nebula in multiple wavelengths Credit NASA JPL Galileo Thermal Radiation An Absolute Temperature Scale Temperature is a measure of the average microscopic motion All thermal motions theoretically cease at Absolute Zero Defined to be 0 Kelvin 0 K Not degrees Kelvin Kelvin Degrees Celsius 273 Wavelength version Thermal Radiation The Blackbody Spectrum Blackbody An idealized body that absorbs and reradiates all wavelengths of light perfectly Y axis is Intensity or simply how much light the brightness Larger values means more of that color X axis is either frequency or wavelength So together a blackbody spectrum tells how much of each wavelength of light a body with a temperature T is giving off emitting B T Frequency version The Planck Function or Blackbody Spectrum Wavelength version Thermal Radiation B T The Blackbody Spectrum Blackbody An idealized body that absorbs and reradiates all wavelengths of light perfectly Characterizes the electromagnetic radiation or light emitted by sufficiently dense objects Reflects the internal thermal motions moving particles with charge Sufficiently dense covers dense gases liquids and solids e g you a planet stars etc As a function of temperature every temp has a unique blackbody spectrum curve Frequency version A Blackbody So what the heck is this imaginary thing called a blackbody I absorb all light that falls on me Perfect Thermal Radiation Out Light energy in And reradiate it as thermal radiation according to my temperature Energy in via light Energy out via light as a Blackbody Curve A Blackbody Intensity Energy into blackbody induces thermal motions which will reradiate according to the temperature UV Laser All the same Perfect Thermal Radiation Out Total Energy in is say 100 units of energy per second hitting the blackbody from the UV laser Energy in via light Intensity Wavelength Total Energy out is also 100 units of energy per second but now spread out over a lot of wavelengths Wavelength Energy out via light as a Blackbody Curve The Blackbody Spectrum Curve Characteristics of Blackbody spectra Mathematical formulation known as the Planck Function it s complicated Every Temperature has a unique blackbody curve associated with it Different curves NEVER overlap B T According to temperature each blackbody curve changes in size area under the curve and location of peak Area under curve is a measure of total amount of light or energy depends on temperature 4 Peak location indicates temperature UNL Blackbody Curves Simulator provides a useful tool to play with these concepts Thermal Radiation Reality versus Ideal Intensity Blackbody An idealized body that absorbs and reradiates all wavelengths of light perfectly T 5800 K At top of atmosphere At sealevel Note that you can see the spectral windows in the sea level spectrum The reason for the difference is a topic of Chapter 4 Spectroscopy Radiation Laws Wein s Law Peak of Emission in wavelength is inversely proportional to temperature in nanometers in microns OR Think of intensity as amount of each color wavelength the object is emitting As Temperature of Blackbody increases the peak in emission decreases to shorter bluer wavelengths In physics and astronomy we denote wavelength with the Greek letter lambda Wein s Law The one that relates peak wavelength to temperature allowing us to measure the temperatures of things in space Wein s Law tells you where the peak of the blackbody spectrum is T 7000 K peak 2900 6000 0 41 m or 410 nm Peak inUV Violet T 6000 K peak 2900 6000 0 48 m or 480 nm Peak in Blue T 4000 K peak 2900 4000 0 725 m or 750 nm Peak in Red T 1000 K peak 2900 1000 2 9 m or 2900 nm Peak in Infrared The Color of Stars Explained Hotter Stars are Blue Cooler Stars are Red A cluster of stars imaged with the Hubble Space Telescope The color of the stars reflects their surface temperature Image Credit NASA HST Medium T Whitish Star Hot Blue Star Cool Red Star The Temperature of the Universe Several satellites have measured the background radiation of the universe Known as the Cosmic Microwave Background Black squares are data measured by the COBE spacecraf Red Curve is the Blackbody Curve for 2 74 K Credit NASA Cobe The Radiation Laws Stefan Boltzmann Law The
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