1. RADIATION AND SPECTRA Chapter 4

9. WAVESWAVES l A stone dropped into a pool of water causes an expanding disturbance called a wave.

10. WAVESWAVES l Light and radio are waves (called electromagnetic radiation) caused by charged particles (mostly electrons) oscillating. l A stone dropped into a pool of water causes an expanding disturbance called a wave. l Sound is a wave caused by a pressure disturbance.

11. PROPERTIES OF RADIATION l Speed = 3 x 10 5 km/s in vacuum. l Radiation often behaves as a wave. l Wavelengths (1nm = 10 -9 m) ä Radio = 1m (10 9 nm) ä Infrared = 10  m (10 4 nm) ä Visible = 0.5  m (500 nm) ä Ultraviolet = 10 nm ä X-ray = 0.1 nm    -ray = 10 -4 nm ä m = metre,  = 10 -6, n = 10 -9

12. ELECTROMAGNETIC RADIATION

13. ELECTROMAGNETIC WAVES

14. HUMAN SENSITIVITY to WAVES l Sound Waves  (wavelength) = pitch  Short = high pitch  Long = low pitch l Light Waves  (wavelength) = colour  Short = bluer  Long = redder

15. NANOMETERNANOMETER Usual unit of for light is nm Usual unit of for light is nm ä(nano-meter = 10 -9 metres) äBlue light = 400 nm äRed light = 700 nm

16. NANOMETERNANOMETER Usual unit of for light is nm Usual unit of for light is nm ä(nano-meter = 10 -9 metres) äBlue light = 400 nm äRed light = 700 nm

17. PROPERTIES OF RADIATION l Speed = 3 x 10 5 km/s in vacuum. l Radiation often behaves as a wave. l Wavelengths (1nm = 10 -9 m) ä Radio = 1m (10 9 nm) ä Infrared = 10  m (10 4 nm) ä Visible = 0.5  m (500 nm) ä Ultraviolet = 10 nm ä X-ray = 0.1 nm    -ray ä m = metre,  = 10 -6, n = 10 -9 l Generally the hotter the source the shorter its emitted wavelength

18. ELECTROMAGNETIC RADIATION Type of Radiation Wavelength Range (nm) Radiated by Objects at this Temperature Typical Sources Gamma rays Less than 0.01 More than 10 8 K Few astronomical sources this hot. Some supernovae, pulsars, black holes and gamma ray quasars. X rays 0.01 - 2010 6 - 10 8 KGas in clusters of galaxies; supernova remnants; solar corona Ultraviolet20-40010 4 - 10 6 KSupernova remnants; very hot stars Visible400-70010 3 - 10 4 KStars Infrared10 3 - 10 6 10 - 10 3 K Cool clouds of dust and gas; planets; satellites RadioMore than 10 6 Less than 10KNo astronomical objects this cold. Radio emission produced by electrons moving in magnetic fields (synchrotron radiation)

19. PROPERTIES OF RADIATION l Speed = 3 x 10 5 km/s in vacuum. l Radiation often behaves as a wave. l Wavelengths (1nm = 10 -9 m) ä Radio = 1m (10 9 nm) ä Infrared = 10  m (10 4 nm) ä Visible = 0.5  m (500 nm) ä Ultraviolet = 10 nm ä X-ray = 0.1 nm    -ray ä m = metre,  = 10 -6, n = 10 -9 l Propagation of radiation

20. PROPAGATION of RADIATION INVERSE SQUARE LAW

21. PROPERTIES OF RADIATION l Speed = 3 x 10 5 km/s in vacuum. l Radiation often behaves as a wave. l Wavelengths (1nm = 10 -9 m) ä Radio = 1m (10 9 nm) ä Infrared = 10  m (10 4 nm) ä Visible = 0.5  m (500 nm) ä Ultraviolet = 10 nm ä X-ray = 0.1 nm    -ray ä m = metre,  = 10 -6, n = 10 -9 l Propagation of radiation l Spectrum of radiation (blackbody)

22. WHITE LIGHT SPECTRUM

23. BLACKBODY RADIATION l Astronomical objects emit energy at different wavelengths

24. ORION CONSTELLATION Rigel Betelgeuse

25. BLACKBODY RADIATION l Astronomical objects emit energy at different wavelengths l Blackbody ä WHY? ä Temperature ä a source that absorbs all radiation hitting it. ä Energy is re-emitted at all wavelengths. ä Spectrum emitted depends on the temperature ä At higher temperatures, more energy is emitted.  F =  T 4 ä The higher the temperature, the shorter is the maximum wavelength.   max (nm) = 2.9 x 10 6 /T(ºK) Q ºK = ºC + 273

26. BLACKBODY CURVES EMITTED ENERGY WAVELENGTH (nm) 0 500 1000 1500 2000 2500 3000 | | | | | | | 3,000 K (960 nm) 4,000 K (725 nm) 5,000 K (580 nm) WIEN’S LAW T = Temp ºK max in nanometers 7,000 K (400 nm)

27. ORION CONSTELLATION Rigel Betelgeuse

28. FLASHCARDFLASHCARD WHAT IS YOUR APPROXIMATE BODY TEMPERATURE IN DEGREES K? A) 100 K B) 200 K C) 300 K D) 400 K

29. FLASHCARDFLASHCARD AT WHAT WAVELENGTH DO YOU PUT OUT MOST OF YOUR ENERGY? A) 100 nm (Ultra violet) B) 1000 nm (deep red) C) 10,000 nm (infrared) D) 1,000,000 nm (short radio)

30. DOPPLER SHIFT

31. Doppler Shift Formula l Change in wavelength = (original wavelength) times (v/c) l c = 300,000 km/sec l eg wavelength 400 nm from source moving ½ c away from you. l l change in wavelength = (wavelength) times (v/c) = (400) times (½) = 200 nm l l wavelength thus observed at 600 nm – colour change from blue to red

32. FLASHCARDFLASHCARD IMAGINE THAT YOU ARE ON A SPACESHIP, SPEEDING TOWARDS MARS (THE RED PLANET). YOU GET CONFUSED AND MISIDENTIFY IT AS EARTH (THE BLUE PLANET). HOW FAST WERE YOU GOING? (c = 3 x 10 5 km/s, blue light = 400 nm, red light = 700 nm) A) 2/7 c ( = 85,700 km/s) B) 3/7 c (= 128,570 km/s) C) 4/7 c (= 171,430 km/s) D) 5/7 c (= 214,290 km/s)