1. The Nature of Light Vanessa Thulsiraj December 10, 2010

2. Light and Astronomy Direct measurement is difficult Direct measurement is difficult Can not take temperature of sun Can not take temperature of sun Can not sample composition of Jupiter’s atmosphere Can not sample composition of Jupiter’s atmosphere Can take indirect measurements by analyzing light Can take indirect measurements by analyzing light Light from far off stars or planets can reveal what the object is made of and its temperature Light from far off stars or planets can reveal what the object is made of and its temperature

3. Light Models Electromagnetic wave or radiation: Light is a mixture of electric and magnetic energy Electromagnetic wave or radiation: Light is a mixture of electric and magnetic energy Wave-particle duality Wave-particle duality Wave nature: Diffraction Wave nature: Diffraction Particle Nature: Reflection Particle Nature: Reflection

4. Electromagnetic Radiation Electric Direction Magnetic Wavelength

5. Electromagnetic Spectrum

6. Electromagnetic Spectrum and Astronomy WavelengthRadiation Use in Astronomy 10-100mRadioActive galaxies 1-10 mmMicrowaveInterstellar clouds 1-1000umInfraredPlanets 400-700nmVisibleStars, Sun 0.1-1nmX raysCollapsed stars

7. X rays: Galaxy cluster Quasar 3C 186 (NASA, Chandra, 10/26/10)

8. Ultraviolet: Stars Hubble Space Telescope, R136 (12/15/09)

9. Infrared: Stars & Planets ESO ADONIS telescope, 6/11/97

10. Microwave: Interstellar clouds M-51 Whirlpool Galaxy

11. Radio waves NRAO (3/12/2001)

12. Energy and Electromagnetic Radiation Light behaves like discrete particles (wave packets) of energy: Photons Light behaves like discrete particles (wave packets) of energy: Photons Energy carried by electromagnetic radiation is determined by its wavelength Energy carried by electromagnetic radiation is determined by its wavelength e=energy h=6.626x10 -34 J*s c=300,000km/s

13. Blackbody Radiation Blackbody: an object that absorbs and re- emits all of the radiation that falls on it. Blackbody: an object that absorbs and re- emits all of the radiation that falls on it. The Energy Spectrum is a graph of radiation versus wavelength. The curve generated for a blackbody is known as the blackbody curve The Energy Spectrum is a graph of radiation versus wavelength. The curve generated for a blackbody is known as the blackbody curve Shape of the curve depends only on temperature. Shape of the curve depends only on temperature.

14. Wein’s Law Wein’s Law: Objects at different temperatures will emit spectra that peak at different wavelengths

15. Math in Science Can use Wein’s law to determine temperature of sun and other blackbody objects Can use Wein’s law to determine temperature of sun and other blackbody objects Radiation’s wavelength and frequency are related by the speed of light, if we know one, we can find the other. Radiation’s wavelength and frequency are related by the speed of light, if we know one, we can find the other. Energy carried by electromagnetic radiation is determined by its wavelength Energy carried by electromagnetic radiation is determined by its wavelength Math helps us understand and interpret scientific data like blackbody curves Math helps us understand and interpret scientific data like blackbody curves