1. ASTR100 (Spring 2008) Introduction to Astronomy Properties of Light and Matter Prof. D.C. Richardson Sections 0101-0106

2. But First…

3. How does gravity cause tides? The Moon’s gravity pulls harder on near side of Earth than on far side. The difference in the Moon’s gravitational pull stretches the Earth.

4. Size of tides depends on the phase of the Moon.

5. Quiz!!!

6. Quiz Write your NAME and SECTION NUMBER on a piece of paper. Now write the answer to the following: The Universal Law of Gravitation F = G M 1 M 2 / d 2 was discovered by: A. Kepler B. Galileo C. Newton D. Einstein Hand in your answer to the TAs.

7. What is light?

9. Light is an electromagnetic wave that transmits energy.

11. Wavelength and Frequency Wavelength  frequency = speed of light = constant (c)

12. The Electromagnetic Spectrum

13. Particles of Light Particles of light are called photons. Each photon has a wavelength and a frequency. The energy of a photon depends on its frequency.

14. Wavelength, Frequency, and Energy  f = c = wavelength f = frequency c = 3.00  10 8 m/s = speed of light E = h  f = photon energy h = 6.626  10 −34 joule  s

16. Thought Question The higher the photon energy… A.…the longer its wavelength. B.…the shorter its wavelength. C.Energy is independent of wavelength.

17. Thought Question The higher the photon energy… A.…the longer its wavelength. B.…the shorter its wavelength. C.Energy is independent of wavelength.

18. What is matter? Matter is made up of chemical elements called atoms, e.g. hydrogen (H). Atoms are made up of electrons, protons, and neutrons. The protons and neutrons make up the atomic nucleus. The electrons are smeared out in a cloud surrounding the nucleus.

19. Atomic Structure

20. Atomic Terminology Atomic Number = # of protons. Atomic Mass Number = # of protons + neutrons.

21. Atomic Terminology Isotope: same # of protons but different # of neutrons, e.g., 4 He, 3 He, etc.

22. Atomic Terminology Ion: an atom missing one or more electrons. E.g., a hydrogen ion is just a single proton. Molecule: two or more atoms joined together, e.g., water (H 2 O).

23. How do light and matter interact? Emission. Absorption. Transmission. Transparent objects transmit light. Opaque objects block (absorb) light. Reflection or scattering.

24. Reflection and Scattering Mirror reflects light in a particular direction. Movie screen scatters light in all directions.

25. Interactions of light with matter Interactions between light and matter determine the appearance of everything around us.

26. Thought Question Why is the rose red? a)The rose absorbs red light. b)The rose transmits red light. c)The rose emits red light. d)The rose scatters red light.

27. Why is the rose red? a)The rose absorbs red light. b)The rose transmits red light. c)The rose emits red light. d)The rose scatters red light.

28. What are the three basic types of spectra? Spectra of astrophysical objects are usually combinations of these three basic types. Continuous Spectrum Emission Line Spectrum Absorption Line Spectrum

29. Introduction to Spectroscopy

30. Three Types of Spectra

31. Continuous Spectrum The spectrum of a common (incandescent) light bulb spans all visible wavelengths, without interruption.

32. Emission Line Spectrum Low-density gas clouds emit light only at specific wavelengths that depend on their composition and temperature, producing bright emission line spectra.

33. Aborption Line Spectrum A gas cloud between us and a light bulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum.