2. RADIATION AND SPECTRA Chapter 4

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

11. 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.

12. 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

13. ELECTROMAGNETIC RADIATION not all reaches Earth’s surface

14. ELECTROMAGNETIC WAVES some telescopes have to be in space

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

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. 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 Prism splits white light into component colours

18. ELECTROMAGNETIC RADIATION Type of Radiation Wavelength Range (nm) Radiated by Objects at this Temperature Typical Sources Gamma raysLess than 0.01 More than 10 8 KFew astronomical sources this hot. Some supernovae, pulsars, black holes and gamma ray quasars.

19. GAMMA RAY SOURCE Black Hole

20. GAMMA RAY SOURCE Pulsar

21. 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 rays0.01 - 2010 6 - 10 8 KGas in clusters of galaxies; supernova remnants; solar corona

22. X-RAY SOURCE Eta Carinae

23. X-RAY SOURCE Brahe’s Supernova 1572

24. 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

25. ULTRAVIOLET SOURCE Supernova Remnant

26. ULTRAVIOLET SOURCE Crab Nebula Supernova Remnant

27. ULTRAVIOLET SOURCE Young Stars

28. 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

29. VISIBLE RADIATION

30. VISIBLE LIGHT SOURCE note various stellar colours Sagittarius Star Cloud

31. VISIBLE LIGHT SOURCE NGC 6543 (Planetary Nebula)

32. VISIBLE LIGHT SOURCE Ring Nebula (Planetary Nebula)

33. 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 KCool clouds of dust and gas; planets; satellites

34. INFRARED SOURCE Betelgeuse - brightest star in Orion

35. INFRARED SOURCE Mars

36. INFRARED SOURCE

37. IINFRARED SOURCE Io

38. INFRARED SOURCE Trifid Nebula IR Image

39. 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)

40. RADIO SOURCE Antennae Galaxies

41. RADIO SOURCE Milky Way Galaxy

42. WINDOWS to the UNIVERSE RadioInfrared Visible Ultraviolet X-Ray Gamma Ray l Many astronomical objects can be observed over a broad band of wavelengths.

43. BROAD BAND SOURCE Optical Infrared Radio Milky Way Galaxy Centre

44. BROAD BAND SOURCE X-ray Optical Ultraviolet Radio The Sun

45. BROAD BAND SOURCE Infrared Optical Radio X-ray Crab Nebula

46. BROAD BAND SOURCE Centaurus A

47. BROAD BAND SOURCE Infrared Optical Radio X-ray Coma Cluster

48. 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

49. PROPAGATION of RADIATION INVERSE SQUARE LAW (Intensity  R -2 )

50. 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)

51. WHITE LIGHT SPECTRUM

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

53. ORION CONSTELLATION Rigel Betelguese

54. 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 then re-emitted at all wavelengths. ä At higher temperatures, more energy is emitted. Q Energy emitted =  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

55. 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)

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

57. 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) Interlude with special camera

58. DOPPLER SHIFT

59. Doppler Shift Formula l l Change in wavelength = original wavelength x v/c l c=300,000 km/sec l eg wavelength 400 nm from source moving ½ c away from you. l change in wavelength = wavelength x v/c = 400 x ½ =200 nm l wavelength thus observed at 600 nm

60. 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)