Newton ’ s Experiments with Light

1. Newton’s Experiments with Light

2. Electomagnetic Waves

3. Properties of Waves: Frequency and Wavelength

5. Radio waves have a) high energy and long wavelength b) low energy and long wavelength c) low energy and short wavelength d) high energy and short wavelength. Share Question

6. Telescopes Yerkes Refractor Arecibo Radio Disk Mauna Kea Hubble Space Telescope

7. Angular Resolution of Telescopes(ability to distinguish nearby things)

8. Sensitivity of Telescopes(ability to see faint things)

9. The Earth’s Shroud • The Earth’s atmosphere acts to “screen” out certain kinds, or bands, of light. • Visible light and radio waves penetrate the atmosphere easiest; the IR somewhat. Most other bands are effectively blocked out. • Consequently, telescopes are built at high altitude or placed in space to access these otherwise inaccessible bands.

10. Transparency of the Atmosphere

11. Transmission with Altitude

12. Illustration of Atmospheric Absorption

13. Flux of Lightflux refers to “brightness” Light carries energy (e.g., perceived warmth from sunlight) How does this energy propagate through space? And how does that relate to the apparent brightness of a source? “Flux” describes how light spreads out in space: with L=luminosity (or power), and d = distance, flux is Watts/square meter = J/s/m2

14. The Inverse Square Law

15. Kirchoff’s Laws • A hot solid, liquid, or dense gas produces a continuous spectrum of emission. • A thin gas seen against a cooler background produces a bright line or emission line spectrum. • A thin gas seen against a hotter source of continuous radiation produces a dark line or absorption line spectrum.

16. Kirchoff’s Laws: Illustrations

17. Blackbodies • A common approximation for the continuous spectrum produced by many astrophysical objects is that a blackbody (or Planckian). • A blackbody (BB) is a perfect absorber of all incident light. • BBs also emit light!

18. Temperature Scales

19. Sample Blackbody Spectra

20. Atomic Physics • Atoms composed of protons, neutrons, and electrons • p and n in the nucleus • e resides in a “cloud” around the nucleus • mp/mn~1 • mp/me~2000

21. The Bohr Atom

22. Atomic Energy Level Diagram

23. A hot, glowing, opaque solid, liquid or gas emits which type of spectrum? a) Continuous. b) Emission lines. c) Absorption lines. Share Question

24. Interaction of Matter and Light • Absorption: Occurs when a photon of the correct energy moves an electron from a lower orbit to an upper orbit. • Emission: Occurs when an electron drops from an upper orbit to a lower one, thereby ejecting a photon of corresponding energy • Ionization: Occurs when a photon knocks an electron free from the atom • Recombination: Capture of a free electron

25. Absorption and Emission

26. Atoms of different elements have unique spectral lines because each element a) has atoms of a unique color b) has a unique set of neutrons c) has a unique set of electron orbits d) has unique photons e) none of the above; spectral lines are not unique to each type of atom. Share Question

27. The Gross Solar Spectrum Blackbody-like Blackbody deviations

28. Spectrum from ETSU’s Observatory • Spectrum of Albireo: • Also beta Cyg • Binary system • Primary is a “Be star”

29. Thermal Motions of Particles in Gases • Speed distribution of particles in a gas depends on: • temperature of the gas • mass of the particles

30. Doppler Shift The Doppler effect is a change in l, n, E (i.e., color) of light when either or both the source and detector are moving toward or away from one another. So, this is a relative effect.

31. Illustration of the Doppler Effect

32. Composition of the Universe