Light and Matter

1. Light and Matter Foundations Unit: Part C

2. Information from the Skies • Andromeda- Our Nearest Galactic Neighbor • 2.5 million light years away • Travel is unattainable • How can we “know” anything about the universe when the objects we’re studying are at such vast distances.

3. Information from the Skies • Laws of Physics are used to Interpret ElectromagneticRadiation (Waves) from space. • Visible Light waves, radio, UV, etc • Radiation- Energy Transfer, physical fingerprint • ALL of the information we get from space comes in some form of “Light”

4. Information from the Skies • Waves- a traveling disturbance • The properties of these waves give us information about how/where they originated. • The wavelength, period, and frequency give us essential information.

5. Information from the Skies • Wave types have a constant speed • Sound 340 m/s • Light 300,000,000 m/s • Higher Frequency  Shorter Wavelength • Lower Frequncy  Longer Wavelength

6. Information from the Skies • Mechanical Waves- most waves require travel through a medium • Electromagnetic Waves- capable of travel through the vacuum of space.

7. Information from the Skies • Created by the interaction of charged particles

8. Information from the Skies • The interactions cause alternating changes in the electric and magnetic fields. • These changes travel as a wave, the only known wave type that can travel through space.

9. The Electromagnetic Spectrum • Visible Light • Isaac Newton • White Light is not “pure,” but made of all colors. • White Light Passes through prism • Disperses into spectrum.

10. The Electromagnetic Spectrum • What determines color? • Each hue is a different frequency (Hz), Wavelength (m) • Our Eyes are sensitive to • Frequencies: 4.3 x 1014 Hz     7.5 x 1014 Hz • Wavelengths: 7.0 x 10-7 m     4.0 x 10-7 m

11. The Electromagnetic Spectrum • Many other types of Electromagnetic Waves • Radio • Microwave • Infrared • Visible • UV • X Ray • Gamma Ray

13. Electromagnetic Spectrum • Small % of radiation reaches the earth’s surface. • Mostly Radio/Visible • Atmosphere is Opaque to (Blocks) • Some Infrared • Most UV • X Ray • Gamma Ray

14. Thermal Radiation • ALL Objects emit radiation at all times. Because • ALL Particles are in constant motion. And • The Hotter the Object, the faster the particles move, the more energy they radiate.

15. Thermal Radiation • Idealized Objects- Blackbodies • Emit radiation over a range of frequencies • Well defined peak radiation intensity at a specific frequency

16. Thermal Radiation • The peak frequency gives us direct information about the temperature of the object. • Cool Gas Cloud: at 60 K, Low Freq. Radio

17. Thermal Radiation • Dim Young Star- At 600 K, Infrared (Young Red Star, Near Orion Nebula)

18. Thermal Radiation • The Sun’s Surface- at 6000 K, Visible

19. Thermal Radiation • Very Bright Stars- at 60,000 K, Ultraviolet (Star Cluster- Omega Centauri)

20. Thermal Radiation • Astronomers Plot the light output of distant objects in a Blackbody curve. • Astronomical Thermometer

22. Spectroscopy • Spectroscope- • Barrier with a small Slit • Prism • Screen/Detector

23. Spectroscopy • A general light source will often emit a continuous spectrum. • A Pure gas will not emit continuous spectra Ex: Hydrogen Gas

24. Spectroscopy • Heated Gases Give off a Specific Pattern of Emission Lines

25. Spectroscopy • These emission spectra are “signatures” or “fingerprints” • Allow us to deduce which element gases are present in a source of light.

26. Spectroscopy • Hot Gases- Emission Spectrum • Cool Gases- Absorption Spectrum • Subtracts certain wavelengths

27. Spectroscopy

28. Spectroscopy • The specific wavelengths for each element correspond to electron energy levels.

29. Spectroscopy • Different combinations of outcomes.

30. The Doppler Effect • EM Radiation interpreted through spectroscopy • New Unrecognized Patterns • Stars consist of elements not found on Earth? • Closer Look Reveals same patterns, shifted

31. The Doppler Effect • The Doppler Effect- shift in wavelength due to movement (think racecar sound) • Moving Towards Observer- Shifted shorter (towards Blue) Blue Shift • Moving Away From Observer- Shifted longer (towards Red) Red Shift

32. The Doppler Effect

33. The Doppler Effect • Understanding the “shift” allows us to determine the motions of nearby stars and distant galaxies, and universe expansion.

34. Recap • What we “know” about distant objects: • Composition- Spectral Analysis (color signatures) • Temperature- Blackbody curves (peak radiation) • Velocity- Doppler Shift (red/blue shift) and • Rotation, Internal Gas Pressure, Magnetic Field with combinations of the above techniques.

35. Telescopes • “Light” is the only information we receive from space. • How do we collect it?

36. Telescopes • Optical Telescopes (Visible Light) • Designed to Capture as much light as possible from a given direction in space. • Refracting Telescope- Earliest Design (uses Lenses)

37. Telescopes • Reflecting Telescope- improved design (subs mirrors for lenses) • avoids color distortion, prismatic effects

38. Telescopes • Types of Reflectors-

39. Telescopes • Prime Focus “Cage”

40. Telescopes • Combinations- Palomar Telescope (Calif.) • Prime, Cassegrain, Coude’

41. Telescope Size • Light Gathering Power • Larger collecting area, better viewing/measurements • Square of the Diameter • 5-m mirror collects 25x more light than a 1-m mirror

42. Telescope Size • Angular Resolution- ability to separate images of close objects. • Is it one oblong object or two separate objects?

43. Telescope Size • Largest Optical Telescope • “Large Binocular Telescope” (LBT) Arizona • Two 8.4 m mirrors (11.9 m equiv.)

44. Limitations • Atmospheric Blurring- • Air Currents, Pressure Differences cause turbulence. • Blur/Smear the image

45. Limitations • Improvements- • CCD chips (image sensors) • Active/Adaptive Optics- control observatory conditions, temperatures, wind, computer controlled mirror etc.

46. Limitations • Operations outside Earth’s Atmosphere • HST (Hubble Space Telescope)

47. Limitations • Next Gen: JWST (James Webb Space Telescope)

48. Invisible Astronomies • Radio- • Telescope Dishes collect radio waves from space • National Radio Astronomy Observatory, Green Bank, WV (150 m dish)

49. Invisible Astronomies • Arecibo Observatory (300 m)

50. Invisible Astronomies • Benefits- • 24 Hrs a day • Detects objects not emitting visible light (cooler objects) • Radio waves are not absorbed by interstellar dust.