Light can be described as both a wave and a particle. As a wave, it travels at 300 million meters per second and is characterized by its wavelength and frequency. The different wavelengths of light make up the electromagnetic spectrum, from radio waves to gamma rays. As the frequency increases, so does the energy of the electromagnetic waves. Light also behaves as particles called photons, which are emitted or absorbed in specific wavelengths by electrons in atoms. This allows spectroscopy to be used to determine the composition of different objects by their emission or absorption spectra.

1. What is Light?

2. Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s trough crest

3. Wavelength (length/cycle) Wavelength (  ): the length of one complete cycle trough crest Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s

4. Wavelength (length/cycle) Amplitude : 1/2 height between trough and crest Amplitude trough crest Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s

5. Wave Speed = wavelength x frequency Wave Speed =  f (length/second) = (length/cycle) x (cycle/second)

6. Light as a Wave Light waves are characterized by a wavelength  and a frequency f c = 300,000 km/s = 3  10 8 m/s l

7. Electromagnetic Waves

8. Light as a Wave Wavelengths of light are measured in units of nanometers (nm) or Å ngstr öm (Å) : 1 nm = 10 -9 m 1 Å = 10 -10 m = 0.1 nm Visible light has wavelengths between 4000 Å and 7000 Å (400 nm – 700 nm) .

9. The Electromagnetic Spectrum Need satellites to observe Wavelength Frequency High flying air planes or satellites

10. Wavelengths and Colors D i f f e r e n t colors of visible light correspond to different wavelengths.

11. Visible Light (VIS) 700 to 400 nm Our eyes are sensitive to this region of the spectrum Red - Orange - Yellow - Green - Blue - Indigo - Violet

12. Solar Radiation The Source for 99.9% of Earth’s Energy

13. Solar Spectrum The sun emits radiation at all wavelengths Most of its energy is in the IR - VIS - UV portions of the spectrum ~50% of the energy is in the visible region ~40% in the near-IR ~10% in the UV Wavelength (m)

14. RADIO WAVES Have the longest wavelengths and lowest frequencies of all the electromagnetic waves. A radio picks up radio waves through an antenna and converts it to sound waves. Each radio station in an area broadcasts at a different frequency. # on radio dial tells frequency. MRI (MAGNETIC RESONACE IMAGING) Uses radio waves with a magnet to create an image

15. MICROWAVES Microwaves —have the shortest wavelengths and the highest frequency of the radio waves. Used in microwave ovens. Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the form of heat to the food. Used by cell phones and pagers. RADAR ( Ra dio D etection a nd R anging) Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.

16. INFRARED RAYS Infrared = below red Shorter wavelength and higher frequency than microwaves. You can feel the longest ones as warmth on your skin Heat lamps give off infrared waves. Warm objects give off more heat energy than cool objects. Thermogram —a picture that shows regions of different temperatures in the body. Temperatures are calculated by the amount of infrared radiation given off. Therefore people give off infrared rays.

17. VISIBLE LIGHT Shorter wavelength and higher frequency than infrared rays. Electromagnetic waves we can see. Longest wavelength= red light Shortest wavelength= violet (purple) light When light enters a new medium it bends (refracts). Each wavelength bends a different amount allowing white light to separate into it’s various colors ROYGBIV.

18. ULTRAVIOLET RAYS Shorter wavelength and higher frequency than visible light Carry more energy than visible light Used to kill bacteria. (Sterilization of equipment) Causes your skin to produce vitamin D (good for teeth and bones) Too much can cause skin cancer. Use sun block to protect against (UV rays)

19. X- RAYS Shorter wavelength and higher frequency than UV-rays Carry a great amount of energy Can penetrate most matter. Bones and teeth absorb x-rays. (The light part of an x-ray image indicates a place where the x-ray was absorbed) Too much exposure can cause cancer (lead vest at dentist protects organs from unnecessary exposure) Used by engineers to check for tiny cracks in structures. The rays pass through the cracks and the cracks appear dark on film.

20. GAMMA RAYS Shorter wavelength and higher frequency than X-rays Carry the greatest amount of energy and penetrate the most. Used in radiation treatment to kill cancer cells. Can be very harmful if not used correctly.

21. SUMMARY All electromagnetic waves travel at the same speed. (300,000,000 meters/second in a vacuum. They all have different wavelength and different frequencies. Long wavelength-  lowest frequency Short wavelength  highest frequency The higher the frequency the higher the energy.

22. Light as Particle Light also behaves like a particle This particle is called a photon The energy of a photon is dependent on its frequency A photon is like a little packet (quantum) of electromagnetic energy.

23. Where do photons come from? Photons come from atoms Atoms absorb and emit photons at certain specific frequencies. This is because the electrons can only be in certain orbitals.

24. Atomic Emission e -

25. This means… Atoms of an specific element absorb or emit only specific frequencies of electromagnetic energy. This is called the absorption or emission spectrum.

26. Using this in astronomy Astronomers can use these spectra to determine the composition of stars and planets and other stellar objects.

27. The Sun’s Emission Spectrum

28. Wave particle duality

29. SUMMARY Light can also behave light particles called photons. These photons come from the electrons in atoms. Because electrons can only be in specific orbitals, only specific frequencies are emitted or absorbed. These specific frequencies (spectrum) can be used to determine what elements are present.

30. Spectroscopy Using wavelength/frequency to determine composition Can use light emitted emission Or light absorbed absorption

31. Light and temperature Electromagnetic spectrum also tells temperature More heat = more energy More energy = higher frequency Higher frequency = More heat

32. Thermal radiation electromagnetic radiation emitted an object because of the object's temperature

33. Temperature of Stars Gamma and x-ray emitters are hottest Blue stars are hotter Red stars are colder Radio emitters are coldest

34. Kelvin Kelvin is the astronomer’s temperature scale Abbreviation : K K= ºC + 273 So… 0K = -273ºC

35. What’s colder than cold? Absolute zero! 0K Absolutely NO atomic motion None Nada Zip Zilch No not even a little. Deep space is just a few degrees above absolute zero

36. Summary Spectroscopy is using electromagnetic radiation to determine composition Thermal radiation is electromagnetic radiation emitted due to temperature This can be used to determine the temperature and composition of stellar objects Absolute zero (0K) is no atomic motion

37. Manipulating Light Manipulating, or working with, light is what astronomers do We have two main ways to manipulate light: Refraction Reflection

38. Refraction Changing the direction of light as it passes through some medium For example: Straw in drink lenses

39. Refraction

40. Refracting Telescope Focus light through a series of lenses Like what Galileo used

41. Reflection Redirection of electromagnetic radiation Can be done with more than just visible light!

42. Reflecting Telescopes Focus light through a series of mirrors Invented by Isaac Newton

43. Reflecting Telescopes Allow for larger telescopes English astronomer William Herschel built this huge reflecting telescope in the late 1700s.

44. Radio Telescopes Work like visible light reflector scopes Use the radio frequencies

45. Radio Telescopes

46. Radio Astronomy Cassiopeia in visible light Cassiopeia A in radio

47. Photoelectric Effect Light hitting an object causes electrons to be released Must be correct wavelength/frequency (amplitude not important)

48. Photoelectric effect in astronomy Solar panels for spacecraft Digital photography

49. Photography in Astronomy As important a development as the telescope Allows for sharing of information Allows for precise measurements