1. ASTRO 101 Principles of Astronomy

2. Instructor: Jerome A. Orosz (rhymes with “boris”) Contact: Telephone: 594-7118 E-mail: jorosz@mail.sdsu.eduorosz@mail.sdsu.edu WWW: http://mintaka.sdsu.edu/faculty/orosz/web/ http://mintaka.sdsu.edu/faculty/orosz/web/ Office: Physics 241, hours T TH 3:30-5:00

3. Text: “Discovering the Essential Universe, Fifth Edition” by Neil F. Comins

4. Course WWW Page http://mintaka.sdsu.edu/faculty/orosz/web/ast101_fall2013.html Note the underline: … ast101_fall2013.html … Also check out Nick Strobel’s Astronomy Notes: http://www.astronomynotes.com/

5. Where: Room 215, physics-astronomy building (PA-215). No appointment needed! Just drop by! When: All semester long, at the following days and times: Monday: 12 – 2 PM; 5 – 6 PM Tuesday: 12 – 2 PM; 5 – 6 PM Wednesday: 12 – 2 PM; 5 – 6 PM Thursday: 1 – 2 PM; 3 – 6 PM Fall 2013

6. Exam 1: N=61 (4 missing) Average = 59.4 low = 27.5, high = 99 A 90%--100% A- 85%--89% B+ 80%--84% B 75%--79% B- 70%--74% C+ 65%--69% C 60%--64% C- 50%--59% D 40%--49% F 0%--39%

7. Homework/Announcements Homework due Tuesday, October 8: Question 5, Chapter 4 (Describe four methods for discovering exoplanets)

8. Coming Up: The 4 forces of Nature Energy and the conservation of energy The nature of light –Waves and bundles of energy –Different types of light Telescopes and detectors Spectra –Emission spectra –Absorption spectra

9. The spectrum Definition and types: –Continuous –Discrete The spectrum and its uses: –Temperature –Chemical composition –Velocity

10. The spectrum A graph of the intensity of light vs. the color (e.g. the wavelength, frequency, or energy) is called a spectrum. A spectrum is probably the single most useful diagnostic tool available in Astronomy.

11. The spectrum A spectrum can tell us about the temperature and composition of an astronomical object. There are two types of spectra of concern here:  Continuous spectra (the intensity varies smoothly from one wavelength to the next).  Line spectra (there are discrete jumps in the intensity from one wavelength to the next).

12. The spectrum Continuous spectrum. Discrete or line spectra. Images from Nick Strobel (http://www.astronomynotes.com)

13. Thermal Spectra The most common type of continuous spectrum is a thermal spectrum. Any dense body will emit a thermal spectrum of radiation when its temperature is above “absolute zero”: –The “color” depends only the temperature; –The total intensity depends on the temperature and the size of the body. This type of radiation is often called “black body” radiation.

14. Thermal Spectra The most common type of continuous spectrum is a thermal spectrum.

15. Black body radiation Sample spectra from black bodies of different temperatures. Note that the area under the curves is largest for the hottest temperature. There is always a well- defined peak, which crudely defines the “color”. The peak is at bluer wavelengths for hotter temperatures.

16. How light interacts with matter and the line spectrum.

17. How Light Interacts with Matter. Atoms are the basic blocks of matter. In the 1850s, it was discovered that an element, when burned, gave off a unique emission line spectrum.

18. How Light Interacts with Matter. An electron will interact with a photon. An electron that absorbs a photon will gain energy. An electron that loses energy must emit a photon. The total energy (electron plus photon) remains constant during this process.

19. How Light Interacts with Matter. Electrons bound to atoms have discrete energies (i.e. not all energies are allowed). Each element has its own unique pattern of energies, hence its own distinct line spectrum. Image from Nick Strobel (http://www.astronomynotes.com)http://www.astronomynotes.com

20. Emission and Absorption Image from Nick Strobel (http://www.astronomynotes.com)http://www.astronomynotes.com

21. Atomic Fingerprints Hydrogen has a specific line spectrum. Each atom has its own specific line spectrum.

22. Atomic Fingerprints These stars have absorption lines with the wavelengths corresponding to hydrogen!

23. Atomic Fingerprints The Sun (and other stars) have absorption lines with the wavelengths corresponding to iron.

24. Atomic Fingerprints. One can also look at the spectra of other objects besides stars, for example clouds of hot gas. This cloud of gas looks red since its spectrum is a line spectrum from hydrogen gas.

25. The Doppler Shift: Measuring Motion If a source of waves is not moving, then the waves are equally spaced in all directions.

26. The Doppler Shift: Measuring Motion If a source of waves is moving, then the spacing of the wave crests depends on the direction relative to the direction of motion.

27. The Doppler Shift: Measuring Motion Think of sound waves from a fast-moving car, train, plane, etc.  The sound has a higher pitch (higher frequency) when the car approaches.  The pitch is lower (lower frequency) as the car passes and moves further away.

28. The Doppler Shift: Measuring Motion If a source of light is moving away, the wavelengths are increased, or “redshifted”.

29. The Doppler Shift: Measuring Motion If a source of light is moving closer, the wavelengths are shortened, or “blueshifted”.

30. The Doppler Shift: Measuring Motion The size of the wavelength shift depends on the relative velocity of the source and the observer.

31. The Doppler Shift: Measuring Motion The size of the wavelength shift depends on the relative velocity of the source and the observer. The motion of a star towards you or away from you can be measured with the Doppler shift.

32. Using a Spectrum, we can… Measure a star’s temperature by measuring the overall shape of the spectrum (essentially its color). Measure what chemical elements are in a star’s atmosphere by measuring the lines. Measure the relative velocity of a star by measuring the Doppler shifts of the lines.

33. Next: Comparative Planetology Outline and introduction to the Solar System Planets around other stars

34. Quick Concept Review Some useful concepts: –Density –Albedo

35. Density and Albedo The concepts of density and albedo are useful in planetary studies. Density = mass/volume –The density of water is 1 gram per cubic cm. –The density of rock is 3 grams per cubic cm. –The density of lead is 8 grams per cubic cm. The density of an object can give an indication of its composition.

36. Density and Albedo The concepts of density and albedo are useful in planetary studies. Albedo = % of incident light that is reflected. –A perfect mirror has an albedo of 100% –A black surface has an albedo of 0%. The albedo of an object is an indication of the surface composition.

37. The Planets Why solar system planets are special:

38. The Planets Why solar system planets are special:  Planets are resolved when seen through telescopes (i.e. you can see the disk, surface features, etc.).

39. The Planets Why solar system planets are special:  Planets are resolved when seen through telescopes (i.e. you can see the disk, surface features, etc.).  You can also send spacecraft to visit them.

40. The Planets Why solar system planets are special:  Planets are resolved when seen through telescopes (i.e. you can see the disk, surface features, etc.).  You can also send spacecraft to visit them.  Stars always appear pointlike, even in the largest telescopes.

41. The Planets Why solar system planets are special:  Planets are resolved when seen through telescopes (i.e. you can see the disk, surface features, etc.).  You can also send spacecraft to visit them.  Stars always appear pointlike, even in the largest telescopes. Also, they are so far away that we cannot send probes to study them.

42. The Solar System The Solar System refers to the Sun and the surrounding planets, asteroids, comets, etc.

43. The Solar System The Solar System refers to the Sun and the surrounding planets, asteroids, comets, etc. Do not confuse “solar system” with “galaxy”: –The solar system is the local collection of planets around the Sun. –A galaxy is a vast collection of stars, typically a hundred thousand light years across.

44. The Solar System Census: There were 5 planets known since antiquity: –Mercury –Venus –Mars –Jupiter –Saturn

45. The Solar System Census: There were 5 planets known since antiquity: –Mercury –Venus –Mars –Jupiter –Saturn Since the 1600s (Kepler, Galileo, Newton), the Earth was considered a planet as well.

46. New Members Uranus: discovered in 1781 by William Herschel.

47. New Members Uranus: discovered in 1781 by William Herschel. Neptune: discovered in 1846 by Johann Galle (based on the predictions of John C. Adams and Urbain Leverrier).

48. New Members Uranus: discovered in 1781 by William Herschel. Neptune: discovered in 1846 by Johann Galle (based on the predictions of John C. Adams and Urbain Leverrier). Pluto: discovered in 1930 by Clyde Tombaugh.

49. New Members Uranus: discovered in 1781 by William Herschel. Neptune: discovered in 1846 by Johann Galle (based on the predictions of John C. Adams and Urbain Leverrier). Pluto: discovered in 1930 by Clyde Tombaugh. Asteroids: thousands, starting in 1801.

50. New Members Uranus: discovered in 1781 by William Herschel. Neptune: discovered in 1846 by Johann Galle (based on the predictions of John C. Adams and Urbain Leverrier). Pluto: discovered in 1930 by Clyde Tombaugh. Asteroids: thousands, starting in 1801. Kuiper Belt Objects: Dozens, starting in the 1980s.

51. Pluto “Demoted”! The definition of a “planet” was changed recently: –Planets: The eight worlds from Mercury to Neptune. Mercury Neptune –Dwarf Planets: Pluto and any other round object that "has not cleared the neighborhood around its orbit, and is not a satellite." –Small Solar System Bodies: All other objects orbiting the Sun. Sun http://www.space.com/scienceastronomy/060824_planet_definition.html

52. The Solar System The planets orbit more or less in the same plane in space. Note the orbit of Pluto. This view is a nearly edge-on view.

53. Classifications of Solar System Objects

54. The Solar System The Solar System refers to the Sun and the surrounding planets, asteroids, comets, etc. The scale of things: –It takes light about 11 hours to travel across the Solar system.

55. The Solar System The Solar System refers to the Sun and the surrounding planets, asteroids, comets, etc. The scale of things: –It takes light about 11 hours to travel across the Solar system. This is 0.001265 years.

56. The Solar System The Solar System refers to the Sun and the surrounding planets, asteroids, comets, etc. The scale of things: –It takes light about 11 hours to travel across the Solar system. This is 0.001265 years. –It takes light about 4.3 years to travel from the Sun to the nearest star.

57. The Solar System The Solar System refers to the Sun and the surrounding planets, asteroids, comets, etc. The scale of things: –It takes light about 11 hours to travel across the Solar system. This is 0.001265 years. –It takes light about 4.3 years to travel from the Sun to the nearest star. –It takes light about 25,000 years to travel from the Sun to the center of the Galaxy.

58. The Solar System The scale of things: –It takes light about 11 hours to travel across the Solar system. This is 0.001265 years. –It takes light about 4.3 years to travel from the Sun to the nearest star. –It takes light about 25,000 years to travel from the Sun to the center of the Galaxy. http://www.space.com/22729-voyager-1-spacecraft-interstellar-space.html

59. Scale Model Solar System Most illustrations of the solar system are not to scale.

60. Scale Model Solar System Most illustrations of the solar system are not to scale. Usually, the size of the planets shown is too large.

61. Scale Model Solar System Build your own scale model of the solar system: http://www.exploratorium.edu/ronh/solar_system/ http://pages.umpi.edu/~nmms/solar/index.htm

62. Scale Model Solar System Build your own scale model of the solar system: http://www.exploratorium.edu/ronh/solar_system/ http://pages.umpi.edu/~nmms/solar/index.htm Conclusion: The solar system is pretty empty

63. Scale Model Solar System Most depictions of asteroids in the movies are wrong…

64. The Scale Model Solar System Most depictions of asteroid fields are also not to scale. Image from the official Star Wars pages

65. The Scale Model Solar System Most depictions of asteroid fields are also not to scale. Image from Star Trek Voyager.

66. Two Types of Planets Planets come in two types: –Small and rocky. –Large and gaseous. Or –Terrestrial –Jovian

67. The Terrestrial Planets The terrestrial planets are Mercury, Venus, Earth (and Moon), and Mars. Their densities range from about 3 grams/cc to 5.5 grams/cc, indicating their composition is a combination of metals and rocky material.

68. The Terrestrial Planets The terrestrial planets are Mercury, Venus, Earth (and Moon), and Mars.

69. The Giant Planets The giant planets are Jupiter, Saturn, Uranus, and Neptune.

70. The Giant Planets The radii are between about 4 and 11 times that of Earth. The masses are between 14 and 318 times that of Earth.

71. The Giant Planets The radii are between about 4 and 11 times that of Earth. The masses are between 14 and 318 times that of Earth. However, the densities are between 0.7 and 1.8 grams/cc, and the albedos are high.

72. The Giant Planets The radii are between about 4 and 11 times that of Earth. The masses are between 14 and 318 times that of Earth. However, the densities are between 0.7 and 1.8 grams/cc, and the albedos are high. The planets are composed of light elements, mostly hydrogen and helium.

73. The Gas Giants The composition of the giant planets, especially Jupiter, is close to that of the Sun. The internal structures of these planets is completely different from that of the Earth. In particular, there is no hard surface. These planets are relatively far from the Sun (more than 5 times the Earth-Sun distance), so heating by the Sun is not a big factor.

74. Next: The formation of the Solar System