Merrimack College Astronomy Fall 2016 Ralph P. Pass

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1 Merrimack College Astronomy 1101 Fall 2016 Ralph P. Pass 1

2 Dates Observing logs due Thursday, 12/8 Field trips must be done by December 12th Final Tuesday 12/13 3:00pm to 6:00pm 2

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5 OBAFGKMLT Obnoxiously Bad Astronomers Forget Genius Kepler's Main Laws Today Our Bad Astronomy Faculty Gave Kids Many Long Tests Only Brave And Fearless Knights Map Lunar Terrain 5

6 Digression How many stars can we see from Merrimack? How many stars could we see in the entire sky? 6

7 So, how many stars can you see? How would you figure this out? Count all the stars you can see! How would you handle the stars below the horizon? What fraction of the sky don t we ever see? 7

8 One way to estimate it Pick a standard area and count the numbers of stars in that area Do this several times Figure out an average number of stars per area Figure out how many standard areas cover the sky Estimate the total number of stars 8

9 Data from the class Based on past results: Our data shows that at Merrimack the range was 0.8 to 5 with an average of 2.2 Why such a large range??? How big was the standard area? 9

10 Data from the class Based on past results: Our data shows that at Merrimack the range was 0.8 to 5 with an average of 2.2 Why such a large range??? How big was the standard area? 10º by 10º or 100 square degrees 10

11 Our estimate There are 41, square degrees in the sky So there are about 412 standard areas in the sky We estimate there are 900 stars visible in the entire sky we can see From Merrimack we can see 86.8% of the sky, so we could see a total of 787 stars during the course of the year. 11

12 Reality? Under dark skies it is reported that you can see about 6,000 stars in the sky over the course of a year (at the equator, but only 5,200 here) We see only about 1/7 of the stars we should Why??? 12

13 San Gimignano Average was 6 so about three times more stars or about 2300! 13

14 Implications of 6,000 visible stars Uncountable stars Your offspring will be as numerous as the stars 14

15 HR Homework 15

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24 Going beyond 60MLyr Vesto Melvin Slipher (American) observed that most galaxies had red doppler shifts (36 of 40) meaning they were moving away. Doppler Shifts are directly related to speed Hubble used Cepheid stars in galaxies to relate speed to distance 24

25 Red Shift and Galaxy Distance 25

26 Hubble s Finding Recession Speed Distance Slope is known as Hubble s Constant v = H0d, today H0 = 70 km/sec per Mpc 26

27 Hubble s Extrapolation 27

28 Distance Ladder The Red Shift Distance relationship is the fourth rung of the distance ladder Good to about 9BLyr Assuming the relationship is true for that large a distance Not good for close objects Due to the expansion of space 28

29 Hubble Determined distance to galaxies (Major Advancement) Determined distance/velocity relationship (Real Major Advancement) 29

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31 Hubble Good but not Perfect Hubble thought evolution on the fork was from left to right Tuning fork classification was interesting and still used today Evolution on fork was exactly backwards! Even the best are not immune to a clunker every once in a while! 31

32 Aside After Messier s list of 110 object many lists were created as telescopes got better Herschel made a list which formed the basis for the New General Catalog of about 7800 objects (numbered with increasing RA) Like stars, deep sky objects have multiple names: M31 = NGC 204 There was a set of these objects that looked decidedly different that the others 15 32

33 Universe of Galaxies As telescopes got larger some nebula exhibited a spiral structure The why was unknown and all nebula were assumed to be similar objects Now we understand that there are supernova remnants and planetary nebula in our galaxy So, spiral nebula were also assumed to be in our galaxy until the advent of photography 12 33

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36 So where are galaxies 16 36

37 Zone of Avoidance?? Astronomers were puzzled by the zone of avoidance Thought this implied these objects knew about the Milky Way and hence were close Did not understand about dust that would block light Example of theories to explain the same observation 37

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39 Types of Galaxies 39

40 Galaxies (M65 and M66) 40

41 M31, M32, M110 Andromeda Galaxy Galaxy 41

42 Galaxy 42

43 Galaxy (M51) 43

44 M51 with Merrimack Telescope 44

45 M51, A Slightly Better View Than Mine 45

46 Galaxy (M33) 46

47 Galaxy 47

48 Galaxies 48

49 Galaxies 49

50 NGC 2903 with Merrimack Telescope 50

51 M82 with Merrimack Telescope 31 51

52 Groups of Galaxies 52

53 Galaxies 53

54 Galaxies I Do Not Image 54

55 Edwin Hubble created this to classify Galaxies He thought evolution was from left to right Actual evolution is closer to being right to left Galaxy Classification 55

56 Spiral Galaxies Spiral structure caused by bursts of star creation due to pressure waves radiating from the center into the gas of the galaxy Increase in pressure initiates gravity collapse 56

57 Missed Galaxies Dwarf galaxies and low surface brightness galaxies biased the data 57

58 Stars in Galaxies Galaxy Type Star Population Spiral I and II Elliptical II Irregular I 58

59 Same Redshift so about the same distance Largest Elliptical Galaxy is about the same size and brightness in each cluster Sixth Rung of the distance ladder Galaxy Clusters 39 59

60 Galaxies Looking at large distances is looking back in time Finite speed of light Can see the earliest galaxies by looking deep Can infer how galaxies evolve Prompted several Hubble Telescope Deep Fields 60

61 Near Galactic Pole Few stars, all the rest are Galaxies!!! 61

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63 Galaxy Evolution 43 63

64 Galaxy Interaction (Cannibalism) 44 64

65 Magellanic Clouds in Radio Waves Caused by interaction with the Milky Way 65

66 Combining Optical and Radio observations 66

67 Other Interacting Galaxies 67

68 Again 68

69 Everywhere! 69

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71 Radio telescopes Radio Telescopes 1931 Karl Jansky of Bell Telephone was studying radio noise from thunderstorms when he discovered a background hiss that appeared every 23h 56m Eventually it was traced to Sagittarius and the center of the Milky Way 71

72 Jansky s Telescope 72

73 The First Radio Astronomer Grote Reber (Illinois) 1937 Read about Jansky findings and build the first true radio telescope, 9.5m diameter (374 ) Published first maps of Radio Radiation in

74 Reber s Telescope 74

75 Radio Astronomy Facts Much work is at a wavelength of 21.1 cm (emission from the most abundant element, Hydrogen) Resolution is inversely proportional to wavelength (Longer wavelengths resolve less). In fact, the initial radio telescope had a spot size of 10 degrees (compare to arc seconds for visible telescopes) Largest steerable radio telescope is in West Virginia (300 ). Second largest is at Jodrell Bank in England 250 The largest radio telescope is at Arecibo, Puerto Rico, 1000 Can be done at anytime (not limited to night) and is not sensitive to clouds (but is sensitive to lightning) 75

76 Arecibo 76

77 Telescope Resolution 77

78 Telescope Resolution Limited size causes diffraction Wave related behavior 78

79 Diffraction Spikes and Rings 79

80 Beating Diffraction Larger Telescopes Smaller apertures imply more diffraction Shorter wavelengths Longer wavelength imply more diffraction Interferometry Combining light from separated telescopes 80

81 Interferometry Pioneered in Physics Michelson used it optically to measure star diameters (1920s) Key elements are distance between collectors and good time synchronization You get the equivalent resolution but not the radiation gathering capability 81

82 Radio Astronomy and Interferometry Interferometry is easier with radio waves because timing requirements are wavelength dependent, so radio waves require less stringent timing Creation of baselines approaching the diameter of the earth For two radio antennae operating at 21.1 cm on opposite sides of the earth, resolution is arc seconds and is not dependent on a steady atmosphere Use Earth rotation to provide geometry needed 82

83 Radio Astronomy and Interferometry - II Irwin Shapiro (MIT) was one of the pioneers and proposed using spare time on Apollo telemetry antennae 1970 Required video tape recorders (50mm wide tape, 24 diameter reels) Special interface equipment and special programming at the sites 83

84 Radio Astronomy and Interferometry - III Resolution at shorter wavelengths is arc seconds (a milliarcsecond or mas) Very Large Array has 27 antennas that can be arranged in a Y of over 36km in diameter Each VLA telescope is 25m in diameter 84

85 VLA Credit: NRAO/AUI/NSF 85

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87 Telescopes What is important What are the key elements of a telescope? Brightness of object? Magnification of an object? Length of telescope? Area seen? Color of telescope tube? 87

88 Telescopes Important Features See fainter objects See finer detail See a large area See it close 88

89 Telescopes Key elements Most important factors Aperture (diameter of front lens) All rays to a common focus (Quality) Eyepiece quality Power (or Magnification) is least important optical related parameter 89

90 Numbers related to telescopes Faintest star you can see Finest separation you can resolve Area of the sky being viewed Magnification 90

91 Earth's Atmosphere 91

92 Earth s Atmosphere So why not just build bigger and bigger telescopes to see more detail? 92

93 Earth s Atmosphere Because of turbulence in the atmosphere! Source of twinkling (lots of twinkling is not a good observing night) Best sites have seeing of about 1 arc second There are 3600 arc seconds per degree Merrimack has seeing of about 2 arc seconds This is the resolution of a 2.5 aperture optical telescope! 93

94 Turbulence Solutions For Radio telescopes use interferometry For optical telescopes use a star (real or artificial) and adjust the mirror as the star moves (adaptive or active optics) Put the telescope into space (e.g., Hubble telescope) More than 50 telescopes have been put into space with Hubble being the largest, 8 aperture 94