Merrimack College Astronomy Fall 2016 Ralph P. Pass

Transcription

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

2 Outline Field Trips Star Coordinates Getting to Galileo 2

3 Field trip Field trip to the Museum of Science for a Planetarium show September 20, 2016 Leave from Cascia Hall Parking lot in a Yellow School Bus at 6:00pm SHARP Return by 9:00pm If you are meeting us there, be in the lobby at 6:45pm 3

4 Second Field Trip We were thinking about October 16th, but my plans have changed and I will not be here I will discuss this more next Tuesday. 4

5 But first a bonus point opportunity (due 09/20/2016) Find a major space or astronomy event that happened on October 4th 5

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11 Locating Stars Where is the White House? 11

12 Locating Stars Where is the White House? 1600 Pennsylvania Avenue 12

13 Locating Stars Where is the White House? 1600 Pennsylvania Avenue Washington, DC 13

14 Locating Stars Where is the White House? 1600 Pennsylvania Avenue Washington, DC USA This is equivalent to identifying star locations by their constellation 14

15 Locating Stars Where is the White House? 15

16 Locating Stars Where is the White House? N W 16

17 Locating Stars Where is the White House? N W Latitude and Longitude The street address is good to about 100 yards, the latitude and longitude to 6 feet If you understand latitude and longitude and have a map, you can find any particular latitude and longitude 17

18 Coordinates on Spheres Name some significant reference points or lines on a globe. 18

19 Coordinates on Spheres Name some significant reference points or lines on a globe. North Pole South Pole Equator Greenwich Meridian International Dateline 19

20 Coordinates on Spheres Name some significant reference points or lines on a globe. North Pole South Pole Equator Greenwich Meridian International Dateline Tropic of Capricorn Tropic of Cancer 20

21 Coordinates on Spheres Which can be uniquely determined and which are arbitrary? 21

22 Coordinates on Spheres Which can be uniquely determined and which are arbitrary? North Pole, South Pole, Equator, Tropic of Capricorn, Tropic of Cancer Greenwich Meridian, International Dateline 22

23 Coordinates on Spheres For a rotating sphere there are three unique points: two axes points and one farthest from the spin axis Maximum distance from spin axis Spin Axis 23

24 Coordinates on Spheres Points a maximum distance from the spin axis are the equator The equator is also the point where the sun passes equally far from directly overhead during the year (North and South) 24

25 Coordinates on Spheres Points a maximum distance from the spin axis are the equator and form a Great Circle The equator is also the point where the sun passes equally far from directly overhead during the year The tropics are where the sun passes overhead exactly once per year Latitude is an angular measure of distance from the equator towards the poles 25

26 Coordinates on Spheres Between the two tropics the sun passes directly overhead twice a year How did the tropics get their names? Longitude has an arbitrary 0 point which has been internationally accepted as the Greenwich Meridian or the Prime Meridian The French still smart from losing the 0 point battle with the British (They call the Greenwich Meridian Paris plus 7 minutes ) Longitude is measured in degrees, just like latitude Somewhere the day must change, hence the international dateline Note the appearance of time when talking about longitude 26

27 Star Coordinates Project the poles and the equator onto the celestial sphere and you get the North Celestial Pole (NCP), the South Celestial Pole (SCP), and the Celestial Equator. Project lines of latitude onto the sky The name for the angular distance from a point to the Celestial Equator is the DECLINATION of the point and is conceptually the same thing as latitude (A point with declination equal to your latitude will pass directly overhead) 27

28 The Path of the Sun Ecliptic (Path of Sun) Lines of Longitude And Latitude Equator 2/3/

29 Star Coordinates To do the equivalent of longitude in the sky we need to pick a 0 point, the point were the Sun crosses the Celestial Equator going North This is the Vernal Equinox also known as the First Point of Aries. Unlike longitude which is measured in degrees from the Prime Meridian, this angle in the sky is measured in time. 29

30 Star Coordinates The stars take one star day to rotate about the earth (One Sidereal Day) The distance from the 0 point is measured by how long after the Vernal Equinox is it before an object is in the same relative location Measured as 0h to 23h 59m s This coordinate is called RIGHT ASCENSION and is conceptually the same as East Longitude One Hour of Right Ascension is 15 degrees 30

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32 Example Coordinates 40 Degrees Vega: 18h 36.9m +38º Degrees 20 Degrees 32

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35 Precession 2000 BC Babylon 35

36 Precession: 1 AD 36

37 Precession: Today 37

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39 Hipparchus 150BC Used parallax to estimate moon s distance Created best star chart before 1500AD Discoverer of precession Highly revered! 39

40 But He reported a new star Despite others seeing it, he was labeled a blasphemer and barely avoided being killed for it! 40

41 More Buts The 'Retrograde problem Planet prediction accuracy was poor, too poor for the working Astrologers 41

42 Retrograde Problem Use a Planetarium Program See APOD, astropix.html, for 42

43 Improving accuracy Claudius Ptolemy (150AD), Egyptian in Alexandria Built on Aristotle and used epicycles to improve prediction of wanderer positions (explaining retrograde motion) and, for computational accuracy, moved the spheres so the Earth was not at the exact center of them (centrally close) Epicycles were smaller crystalline spheres attached to the larger main spheres for each body. This theory was embraced by the Christian Church 43

44 Cosmology Epicycles - II 44

45 Cosmology Epicycles - III 45

46 Cosmology Epicycles - IV 46

47 But This was quantified (for prediction purposes) More and more epicycles were added to get accuracy 47

48 Middle (Dark) Ages Science was preserved in Arabic cultures while Europe was in the dark ages 1450 in Florence and Rome started to see the return of Europe to the Hipparchus tradition of careful sky observations New instrumentation and use of trigonometry Suggested change in Aristotle/Ptolemy to view the Mercury and Venus spheres to go around the Sun and simplify calculations (the first break in the Earth being the absolute center of the universe, but Mercury and Venus were viewed as still going around the Earth) 48

49 Copernicus I 49

50 Copernicus II Niklas Koppernigk (Nicholas Copernicus) Born in Poland ( ) most of his work was done in Krakow Placed the Sun at the center and all spheres rotating about the Sun Conceptually simpler than Ptolemy but still needed Epicycles! Computationally simpler as well Predictive accuracy was about the same as the Ptolemaic system Published at his death (although he was a priest, this was still heresy, and he was not insensitive to the opinion of the Church) Colleague inserted For computation only 50

51 Copernius III 51

52 Ptolemy and Copernicus 52

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54 In the Salt Mines Outside Krakow 54

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56 Clocks were a big deal 56

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58 Copyright 2011 Ralph P. Pass 20 58

59 Clock in Prague's Main Square 59

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62 Bonus Op (Due 09/22/2016) Provide a paragraph on the clock in Prague square (in your own words) 62

63 Brahe - II Tycho Brahe ( ) Dane, with most of his work at Uraniborg (island near Copenhagen), building a significant observatory with many new types of instruments Concluded work in Prague Most meticulous and accurate naked-eye observer before telescopes His records were very accurate, highly prized, and closely held Was appalled at Copernicus lack of accuracy in observations (and therefore rejected Copernicus theory) Discovered a Supernova and showed it was more distant than the Moon Showed that comets were more distant that the Moon Very arrogant and short tempered 63

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65 Brahe - II 65

66 Kepler - I 66

67 Kepler II Johannes Kepler ( ) Mathematician, became an apprentice to Brahe to get access to observations (Brahe pleaded with him not to move the Earth from the center of the Universe) Last major Astronomer to put any stock in astrology Changed Copernican system to be Ellipses with the sun at one focus (1 st Law) Equal areas in equal time (so when further from the sun a planet moved slower) (2 nd Law) a³/p² is constant (3 rd Law) Accuracy significantly improved and was the final push to dump the Ptolemy and Aristotle model, at least for calculations Scholarly and unassuming, a man of few social graces 67

68 Kepler's 'Big' Breakthrough Determining distances to the planets (periods were easily known) Earth at observation times Mars at the same point in its orbit (one revolution apart) Earth s Orbit Mars Orbit 68

69 Kepler's Second Law Area 1 Sun Area 2 69