Phases of ma*er strongly depend on temperature

Transcription

1 Phases of ma*er strongly depend on temperature

2 Light and Atoms Remember that each electron is only allowed to have certain energies in an atom. Electrons can absorb light and gain energy or emit light when they lose energy. It is easiest to think of light as a photon when discussing its interacaon with ma*er. Only photons whose energies (colors) match the jump in electron energy levels can be emi*ed or absorbed.

3 Emission Spectra Every atomic gas has its own fingerprint Hydrogen Mercury Helium

4 If light shines through a gas, each element will absorb those photons whose colors match their electron energy levels. AbsorpAon Spectra The resulang absorp'on line spectrum has all colors minus those that were absorbed. We can determine which elements are present in an object by idenafying emission & absorpaon lines.

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6 Rules for Emission by Opaque Objects 1. Ho*er objects emit more total radiaaon per unit surface area. Stephan Boltzmann Law E = σt 4 2. Ho*er objects emit bluer photons (with a higher average energy.) Wien s Law λ max = 2.9 x 10 6 / T(K) [nm]

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8 How do we interpret an actual spectrum? By carefully studying the features in a spectrum, we can learn a great deal about the object that created it.

9 What is this object? Reflected Sunlight: ConAnuous spectrum of visible light is like the Sun s except that some of the blue light has been absorbed object must look red

10 What is this object? Thermal RadiaAon: Infrared spectrum peaks at a wavelength corresponding to a temperature of 225 K

11 What is this object? Carbon Dioxide: AbsorpAon lines are the fingerprint of CO 2 in the atmosphere

12 What is this object? Ultraviolet Emission Lines: Indicate a hot upper atmosphere

13 What is this object? Mars!

14 What have we learned? What are the three basic type of spectra? ConAnuous spectrum, emission line spectrum, absorpaon line spectrum How does light tell us what things are made of? Each atom has a unique fingerprint. We can determine which atoms something is made of by looking for their fingerprints in the spectrum.

15 The Doppler Effect Change in the apparent wavelength/frequency of a wave

16 How does light tell us the speed of a distant object? The Doppler Effect

17 Measuring the Shil StaAonary Moving Away Away Faster Moving Toward Toward Faster We generally measure the Doppler Effect from shils in the wavelengths of spectral lines

18 Doppler shil tells us ONLY about the part of an object s moaon toward or away from us:

19 Spectrum of a RotaAng Object Spectral lines are wider when an object rotates faster

20 What have we learned? How does light tell us the speed of a distant object? The Doppler effect tells us how fast an object is moving toward or away from us. Blueshil:objects moving toward us Redshil: objects moving away from us How does light tell us the rotaaon rate of an object? The width of an object s spectral lines can tell us how fast it is rotaang

21 Chapter 6 Telescopes: Portals of Discovery

22 6.1 Eyes and Cameras: Everyday Light Sensors Our goals for learning: How does your eye form an image? How do we record images?

23 How does your eye form an image?

24 RefracAon RefracAon is the bending of light when it passes from one substance into another Your eye uses refracaon to focus light

25 Example: RefracAon at Sunset Sun appears distorted at sunset because of how light bends in Earth s atmosphere

26 Focusing Light RefracAon can cause parallel light rays to converge to a focus

27 Image FormaAon The focal plane is where light from different direcaons comes into focus The image behind a single (convex) lens is actually upside down!

28 How do we record images?

29 Focusing Light Digital cameras detect light with chargecoupled devices (CCDs) A camera focuses light like an eye and captures the image with a detector The CCD detectors in digital cameras are similar to those used in modern telescopes

30 What have we learned? How does your eye form an image? It uses refracaon to bend parallel light rays so that they form an image. The image is in focus if the focal plane is at the reana. How do we record images? Cameras focus light like your eye and record the image with a detector. The detectors (CCDs) in digital cameras are like those used on modern telescopes

31 6.2 Telescopes: Giant Eyes Our goals for learning: What are the two most important properaes of a telescope? What are the two basic designs of telescopes? What do astronomers do with telescopes?

32 What are the two most important properaes of a telescope? 1. Light collec'ng area: Telescopes with a larger collecang area can gather a greater amount of light in a shorter Ame. 2. Angular resolu'on: Telescopes that are larger are capable of taking images with greater detail.

33 Light CollecAng Area A telescope s diameter tells us its lightcollecang area: Area = π(diameter/2) 2 The largest telescopes currently in use have a diameter of about 10 meters

34 Bigger is be*er

35 Thought QuesAon How does the collecang area of a 10 meter telescope compare with that of a 2 meter telescope? a) It s 5 Ames greater. b) It s 10 Ames greater. c) It s 25 Ames greater.

36 Thought QuesAon How does the collecang area of a 10 meter telescope compare with that of a 2 meter telescope? a) It s 5 Ames greater. b) It s 10 Ames greater. c) It s 25 'mes greater.

37 TMT: Thirty Meter Telescope (Hawaii?) Caltech, UC, others GMT: Giant Magellan Telescope (Chile?) Arizona, Texas A&M, others

38 The minimum angular separaaon that the telescope can disanguish. Angular ResoluAon

39 Angular ResoluAon Ultimate limit to resolution comes from interference of light waves within a telescope. Larger telescopes are capable of greater resolution because there s less interference

40 Angular ResoluAon Ultimate limit to resolution comes from interference of light waves within a telescope. Larger telescopes are capable of greater resolution because there s less interference

41 What are the two basic designs of telescopes? Refrac'ng telescope: Focuses light with lenses Reflec'ng telescope: Focuses light with mirrors

42 RefracAng Telescope RefracAng telescopes need to be very long, with large, heavy lenses

43 ReflecAng Telescope ReflecAng telescopes can have much greater diameters Most modern telescopes are reflectors

44 Mirrors in ReflecAng Telescopes Twin Keck telescopes on Mauna Kea in Hawaii Segmented 10-meter mirror of a Keck telescope

45 What do astronomers do with telescopes? Imaging: Taking pictures of the sky Spectroscopy: Breaking light into spectra Timing: Measuring how light output varies with Ame

46 Imaging Astronomical detectors generally record only one color of light at a Ame Several images must be combined to make full color pictures

47 Imaging Astronomical detectors can record forms of light our eyes can t see Color is someames used to represent different energies of nonvisible light

48 Spectroscopy Light from only one star enters Diffraction grating breaks light into spectrum A spectrograph separates the different wavelengths of light before they hit the detector Detector records spectrum

49 Spectroscopy Graphing relaave brightness of light at each wavelength shows the details in a spectrum

50 Timing A light curve represents a series of brightness measurements made over a period of Ame

51 What have we learned? What are the two most important properaes of a telescope? CollecAng area determines how much light a telescope can gather Angular resoluaon is the minimum angular separaaon a telescope can disanguish What are the two basic designs of telescopes? RefracAng telescopes focus light with lenses ReflecAng telescopes focus light with mirrors The vast majority of professional telescopes are reflectors

52 What have we learned? What do astronomers do with telescopes? Imaging Spectroscopy Timing

53 6.3 Telescopes and the Atmosphere Our goals for learning: How does Earth s atmosphere affect groundbased observaaons? Why do we put telescopes into space?

54 How does Earth s atmosphere affect ground based observaaons? The best ground based sites for astronomical observing are Calm (not too windy) High (less atmosphere to see through) Dark (far from city lights) Dry (few cloudy nights)

55 Light PolluAon Sca*ering of human made light in the atmosphere is a growing problem for astronomy

56 Twinkling and Turbulence Star viewed with ground-based telescope Same star viewed with Hubble Space Telescope Turbulent air flow in Earth s atmosphere distorts our view, causing stars to appear to twinkle

57 AdapAve OpAcs Without adaptive optics With adaptive optics Rapidly changing the shape of a telescope s mirror compensates for some of the effects of turbulence

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59 Calm, High, Dark, Dry The best observing sites are atop remote mountains Summit of Mauna Kea, Hawaii

60 Why do we put telescopes into space?

61 Transmission in Atmosphere Only radio and visible light pass easily through Earth s atmosphere We need telescopes in space to observe other forms

62 What have learned? How does Earth s atmosphere affect groundbased observaaons? Telescope sites are chosen to minimize the problems of light polluaon, atmospheric turbulence, and bad weather. Why do we put telescopes into space? Forms of light other than radio and visible do not pass through Earth s atmosphere. Also, much sharper images are possible because there is no turbulence.

63 6.4 Eyes and Cameras: Everyday Light Sensors Our goals for learning: How can we observe nonvisible light? How can mulaple telescopes work together?

64 How can we observe nonvisible light? A standard satellite dish is essenaally a telescope for observing radio waves

65 Radio Telescopes A radio telescope is like a giant mirror that reflects radio waves to a focus