Merrimack College Astronomy Spring 2017 Ralph P. Pass

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1 Merrimack College Astronomy 1101 Spring 2017 Ralph P. Pass 1

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5 Consider Naming 6,000 stars! There are more than 1,500,000 stars brighter than 12th magnitude There are 700,000 words in the English Language How to id stars? 5

6 Options Name each one (how creative do you want to be?) With the advent of the telescope there were many, many new stars to try to label Naming individual stars was judged to be a dead end. So systematic means were developed to identify stars. 6

7 Johann Bayer Defined an alphabetic ordering of stars in a constellation. The alphabet was the Greek alphabet and was more or less by magnitude. The proper way of using this system is to give the Greek letter and the genetive version of the constellation name. For example, Betelgeuse, is Alpha Orionis (literally Alpha of Orion or Orion s Alpha) Astronomers use the short hand: α Ori So, Betelgeuse or α Ori are the same star However, with only 24 letters, they ran out 7

8 Our Friend Orion α Ori δ Ori γ Ori ε Ori ζ Ori χ Ori β Ori 8

9 The Big Dipper (part of Ursa Major) is an exception to brightness rule α η ζ ε δ γ β UMa or Ursa Majoris 9

10 John Flamsteed First Astronomer Royal (1675) Numbered stars in a constellation going from west (lower RA) to east (higher RA) Stars now had as many as three identifiers: Betelgeuse α Ori 58 Ori (58 Orionis) Rigel (β Ori, 19 Ori) 10

11 Canis Major, the Big Dog What happens when you run out of alphabet? 11

12 The Pleiades 12

13 A good question. Which of the following is further east? 1 Ori 10 Ori 20 Ori 100 Ori 13

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26 Ancient Astronomers List stars by category The first category contained the brightest stars The sixth category contained the stars just visible The categories were called magnitudes Not all first magnitude stars appeared to be the same brightness Qualitative Inverse scale (smaller numbers are brighter) 26

27 Scientific Astronomers Wanted to quantify magnitudes (so in particular we could assign magnitudes to the stars we see in a telescope) and relate magnitude to watts per area. They determined that on the average, a one magnitude difference was a difference in energy of about a factor of 2.5 They defined a five magnitude difference to be exact 100 times more (or less) energy 27

28 Magnitude Table Magnitude difference Energy Factor

29 Comet 17P/Holmes, Oct It brightened from Magnitude 17 to Magnitude 2 (in less than a day) Difference is 15 magnitudes Energy change was a factor of 100 * 100 * 100 or 1,000,000 29

30 Telescopes 30

31 Focusing Light 31

32 Focusing Light Visible Light Refractors (Galileo) Reflectors (Newton) Radio waves X-Rays Grazing-incidence mirrors 32

33 Refraction Light Refraction is caused by a difference in the Speed of Light in media The universal speed limit is the speed of light in a vacuum. It is possible to go faster than the speed of light if you are not in a vacuum!!!!! In these cases there is the equivalent of a sonic boom Glass 33

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35 Telescopes 35

36 Telescopes 36

37 Telescopes Invented 1608 in Holland Used two lenses to see far things close up The Dutch also created Microscopes 70 37

38 Telescopes Basics A lens to focus the incoming light One lens to look at the focused image In this case both lenses are positive Parallel Light Rays Focus Point Parallel Light Rays 38

39 Telescopes Basics The front lens makes an image of the far object (like a camera lens) The second lens acts as a magnifying glass to look at the image Parallel Light Rays Focus Point Parallel Light Rays 39

40 Telescopes Galileo s Galilean telescope uses a positive and a negative lens Parallel Light Rays Focus Parallel Light Rays 40

41 Telescope - terms The big lens is the collector or the objective The small lens is the eyepiece The distance from the center of a lens to the focus point (for incoming parallel light rays) is the focal length The diameter of a lens is its aperture 41

42 Telescopes First types Galilean telescopes have erect images and have limited power and view (great for daytime uses) Positive lens or eyepieces always invert image Telescopes like this are called REFRACTORS For the first century of telescopes the only telescopes were REFRACTORS 75 42

43 Example Telescopes - I Hevelius 130 foot Telescope in Danzig (now Gdansk) 76 43

44 Reflection 44

45 Using a Mirror in a Telescope Curved Mirror Focus Point Parallel Light Rays from Source 45

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47 The Problem with Reflector Where does the observer s Head go For initial telescope attempts, the mirror was several inches across, so a head would block the entire telescope This was the design by Da Vinci, 100 years before the telescope was invented 47

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49 Telescopes 49

50 Newton s Telescope Curved Mirror Flat Secondary 50

51 Newton s Telescope Newtonian Telescope Secondary blocks some of the mirror This reduces light and makes the image fuzzier How to make the mirror (material, coating)? Refractors were typically sharper than reflectors Reflectors were cheaper than Refractors for the same size objective (Same light gathering ability) Newtonian telescopes and refractors were roughly the same length for the same focal length 51

52 Model of Newton s First 52

53 Example Telescopes - II Herschel s 48, 28 foot telescope 82 53

54 Odd looking telescopes 83 54

55 Telescopes Make things brighter Make things sharper Make things closer 55

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