1. Astronomy 100 Tuesday, Thursday 2:30 - 3:45 pm Tom Burbine tburbine@mtholyoke.edu www.xanga.com/astronomy100

2. Help Desk There is an Astronomy Help Desk in HAS 205. It will be open from Monday through Thursday from 7-9 pm.

3. E = mc 2 and KE = 1/2 mv 2 HW Purpose of this Homework To teach you that if you can get lots of energy from a small amount of material if you can turn all the matter into energy You need a much bigger mass to produce the same amount of energy through kinetic energy (through impact with a velocity)

4. The nuclear bomb dropped on Hiroshima released 8.4 x 10 13 joules of energy. What would be the mass of nuclear material that would produce this amount of energy if you assume all the nuclear material was converted to energy? Show your work. E = mc 2 M=E/c 2 c = 3 x 10 8 m/s c 2 = 9 x 10 16 m 2 /s 2 M = 8.4 x 10 13 J / 9 x 10 16 m 2 /s 2 M = 9.3 x 10 -4 kg

5. An asteroid is on a collision course with Earth? What must the mass of the asteroid be to produce that much energy (8.4 x 10 13 joules) if it hits the Earth with a velocity of 20 km/s (20,000 m/s)? Show your work. KE = kinetic energy KE = ½ m v 2 m = KE/(½ v 2 ) m = 2KE/v 2 m = 2* 8.4 x 10 13 J/(20000*20000) m = 4.2 x 10 5 kg

6. Also You need to list units for answer!!!!!! Like kilograms for the previous questions

7. Element Homework So you learn that there are lots of elements with different properties And each element has a number of isotopes Isotope – same number of protons, different number of neutrons

8. Latest Homework Was not done to torture you Was done so you realize that different planets have different accelerations due to gravity and different escape velocities How would that information be used on a test?

9. For example, A body is the same size as the Earth but has twice the Earth’s mass. What would be the acceleration of gravity on this body? A) 4.9 m/s 2 B) 9.8 m/s 2 C) 19.6 m/s 2 D) 2.45 m/s 2 E) 39.2 m/s 2

10. For example, A body is the same size as the Earth but has twice the Earth’s mass. What would be the acceleration of gravity on this body? A) 4.9 m/s 2 B) 9.8 m/s 2 C) 19.6 m/s 2 D) 2.45 m/s 2 E) 39.2 m/s 2 Because of formula F = G M 1 M 2 d 2

11. Homework Assignment (Due Thursday March 3 rd ) Make up a test question Multiple Choice A-E possible answers 1 point for handing it in 1 point for me using it on test The question needs to be on material that will be on the March 10 th exam

12. Next Homework (due Tuesday, March 1 st ) In Joules, calculate the typical energy of one –Gamma ray –X-ray –Ultraviolet light –Visible light –Infrared light –Radio wave photon

13. Light Light is a form of energy

14. Light These are all forms of light –Gamma rays –X-rays –Ultraviolet light –Visible light –Infrared light –Radio waves

15. Light Can act as a particle Can also act as a wave

16. Particle aspect Particles called photons stream from the Sun and can be blocked by your body

17. Wave aspect

18. Thomas Young Experiment http://micro.magnet.fsu.edu/primer/java/interferen ce/doubleslit/http://micro.magnet.fsu.edu/primer/java/interferen ce/doubleslit/

19. Characteristics of waves velocity = wavelength x frequency Wavelength = distance Frequency = cycles per second = hertz

20. For light c = wavelength x frequency In vacuum, speed of light stays the same So if wavelength goes up Frequency does down f = frequency λ = wavelength c = λ x f

21. Show animation Electromagnetic spectrum

22. Calculations c = λ x f So if the wavelength is 1 x 10 -12 m 3 x 10 8 m/s = 1 x 10 -12 m * f f = 3 x 10 8 m/s/1 x 10 -12 m f = 3 x 10 20 s -1 = 3 x 10 20 Hz

23. Calculations c = λ x f So if the frequency is 1 x 10 15 Hz 3 x 10 8 m/s = λ * 1 x 10 15 Hz λ = 3 x 10 8 m/s/1 x 10 15 Hz λ = 3 x 10 -7 m

24. Energy of light Energy is directly proportional to the frequency E = h * f h = Planck’s constant = 6.626 x 10 -34 J/s since f = c/λ Energy is inversely proportional to the wavelength E = hc/λ

25. Higher the frequency, Higher the energy of the photon Higher the wavelength, Lower the energy of the photon

26. Calculations What is the energy of a radio wave with a frequency of 1 x 10 7 Hz? E = h * f h = Planck’s constant = 6.626 x 10 -34 J/s E = 6.626 x 10 -34 J/s * 1 x 10 7 E = 6.626 x 10 -27 J

27. Calculations What is the energy of a gamma ray photon with wavelength of 1 x 10 -15 m E = hc/λ h = Planck’s constant = 6.626 x 10 -34 J/s E = 6.626 x 10 -34 J/s * 3 x 10 8 m/s / 1 x 10 -15 m E = 1.99 x 10 -10 J

28. Next Homework (due Tuesday, March 1 st ) In Joules, calculate the typical energy of one –Gamma ray –X-ray –Ultraviolet light –Visible light –Infrared light –Radio wave photon

29. So why are some types of radiation dangerous? Higher the energy, the farther the photons can penetrate So gamma and X-rays can pass much more easily into your the body These high-energy photons can ionize atoms in cells Ionization means removes electrons from an atom

30. More dangerous

31. When you measure an astronomical body You measure intensity Intensity – amount of radiation

32. How do you use light to determine what is in an astronomical body?

33. electrons

34. Energy levels where an electron can reside To go to a higher energy level, an electron needs to gain energy To go to a lower energy level, an electron needs to lose energy

35. Rules An electron can not jump to a higher energy level unless it gains energy from somewhere else –Absorbs a photon –Gains kinetic energy from an impacting particle To go to a lower energy level, the electron must lose energy –Emits a photon Electron jumps can occur only with the particular amounts of energy representing differences between possible energy levels

36. So which of these transitions is not possible A B C D E

38. So which of these transitions is not possible A B C D E

39. Show animation Production of emission lines

40. Heated hydrogen gas Emission line spectrum White light through cool hydrogen gas Absorption line spectrum

41. Show animation Production of absorption lines

42. Types of spectra Emission – radiation is emitted at characteristic wavelengths –Material is “hot” so electrons keep on bumping into each other and transferring kinetic energy toe ach other so they jump between particular energy levels Absorption – radiation is absorbed at characteristic wavelengths –Radiation passes through the material

43. So why is this important Different elements have different number of electrons Different elements have different energy levels for their electrons

44. So Different elements can absorb light at specific energies Different elements can emit light at specific energies So if you can measure the wavelength of the light from an astronomical body, you can determine whats in it

45. Emission line spectra

46. Show animation Composition of a mysterious gas

47. How can you all this to determine velocities? Doppler Shift – The wavelength of light changes as the source moves towards or away from you Since you know the wavelength position of emission or absorption features If the positions of the features move in wavelength position, you know the source is moving

49. So Source moving towards you, wavelength decreases Source moving away from you, wavelength increases

50. Questions?