Buy-back points tallied and added: 750 points bought-back. Last Withdrawal date: this friday, Oct 31st.

Transcription

1 Announcements HW #3: Available online now. Due in 1 week, Nov 3rd, 11pm. Buy-back points tallied and added: 750 points bought-back. Last Withdrawal date: this friday, Oct 31st. Evening Observing: next four nights, 8:30 9:45pm. WEATHER PERMITTING.

2 Of Sunspots and the Earth Question #1 on Exam 2: many of your secondguessed yourselves. Sunspots are about the same size as earth, some smaller, some bigger. But, figure 6.2 says a sunspot could swallow several earths. The biggest could. Since this was confusing, if you changed your correct answer in the buy-back extra-credit, you got full points (+2).

3 The image at right shows a picture of the Sun. The dark spots located on this image are sunspots. How does the size of Earth compare (approximately) to the size of the sunspot that is identified on the image of the Sun? Sunspot A) Earth and the sunspot are about the same size. B) The sunspot is much larger than Earth. C) The sunspot is much smaller than Earth.

4 The image at right shows a picture of the Sun. The dark spots located on this image are sunspots. How does the size of Earth compare (approximately) to the size of the sunspot that is identified on the image of the Sun? Sunspot A) Earth and the sunspot are about the same size. B) The sunspot is much larger than Earth. C) The sunspot is much smaller than Earth.

5 Last Time Light: carrier of information from the universe. Visible light just a tiny portion of all the electromagnetic spectrum. Even radio is a form of light. Light has a wavelength and frequency. High frequency=high energy=show wavelength, and visa versa.

6 Last Time Matter, composed of atoms, identified by atomic number (number of protons). This sets their properties. Isotopes have same number of protons, but different number of neutrons (e.g. Carbon 13). Light and matter interact by emission/ absorption/reflection/transmission.

7 Last Time The Spectrum of a source describes its intensity at each wavelength of light. There is a special spectrum of perfectly black emission, called blackbody. Most objects, including stars, emit a spectrum close to blackbody radiation. Hotter blackbody = shorter wavelength of peak emission.

8 The filter experiment (take 2) A red object absorbs all but red light. A red filter transmits all but red light.

9 High energy, short wavelength, high frequency Electromagnetic Spectrum Visible light: red, orange, yellow, green, blue, indigo, violet (ROY G BIV) Invisible Light: Ultraviolet = bluer than blue Infrared = redder than red (heat!) Other wavelengths: Short: X-rays, gamma-rays Long: microwave, radio Low energy, long wavelength, low frequency

10 Spectroscopy Prism separates light into different colors Continuous spectrum contains all colors Example: blackbody spectrum

11 Spectroscopy Absorption Line spectrum Some colors are missing (discrete lines)

12 The Solar Spectrum

13 The Solar Spectrum H Mg Na

14 Spectroscopy Emission Line spectrum Only certain colors are present (discrete lines) Spectrum for each element unique (like fingerprints)

15 How it Works

16 Thought question Which letter(s) mark absorption lines? A B C D E

17 Thought question Which letter(s) mark absorption lines? A B C D E

18 Thought question Which letter(s) mark Emission lines? A B C D E

19 Thought question Which letter(s) mark Emission lines? A B C D E

20 Doppler Shift (again) Just like a train, the pitch (frequency) of light changes if the light source is moving. Moving away: redshifted. Moving towards: blueshifted.

21 The Doppler Effect ONLY tells us the about an objects motion towards or away from us

22 Thought Question: You measure a line of hydrogen at nm in the lab. The same line has a wavelength of 659 nm in a star. The star: a) is moving away from you b) is moving towards you c) is not moving at all

23 Thought Question: You measure a line of hydrogen at nm in the lab. The same line has a wavelength of 659 nm in a star. The star: a) is moving away from you b) is moving towards you c) is not moving at all

24 Model Atom Electrons orbit nucleus Number of electrons = number of protons Ionization = removing electrons Only certain orbits are allowed hydrogen helium

25 Atomic Energy Levels In order to move between orbits (levels), the electron need gain or lose a specific amount of energy, and only that amount. level 3 level 2 level 1 1 H not to scale 1 ev (electron Volt) = 1.6 x J

26 Atomic Absorption Atom absorbs photon energy electron jumps to higher energy orbit only certain discrete orbits are allowed Atom can absorb only discrete colors (energies)

27 Atomic Emission Electron jumps to a lower energy orbit Atom emits photon can emit only discrete colors same colors (wavelengths/ energies) as absorption

28 Chemical Fingerprints each element or molecule has: a unique set of energy levels, and so a unique emission/absorption line spectrum we can determine the composition of a gas by looking at its spectrum!

29 Spectrum Demo Get a grating. Hold it up and look through it at the lamps. Should see various Rainbows going off in several directions. Please return at the top of the table, at the end of class.

30 Sun

31 Sun Hydrogen Helium Carbon Nitrogen Oxygen Neon Sodium Magnesium Aluminum Silicon

32 What can we learn Light can tell us: the temperature of an object. It s chemical composition (what it s made of!). Velocity of motion....much more (from across the universe!).

33 Workbook Time Analyzing Spectra, Page 69.

34 Consider the two spectral curves for Star V and Star Y shown in the graph at right. What can you determine about the relative temperatures of the two stars? A) Star V is at the higher temperature. B) Star Y is at the higher temperature. C) Both stars are the same temperature. D) The relative temperatures of the stars cannot be determined

35 Consider the two spectral curves for Star V and Star Y shown in the graph at right. What can you determine about the relative temperatures of the two stars? A) Star V is at the higher temperature. B) Star Y is at the higher temperature. C) Both stars are the same temperature. D) The relative temperatures of the stars cannot be determined

36 Red Hydrogen Line

37 Yellow Sodium Lines

38 Telescopes Eyes on the Heavens

39 What good are telescopes? Like giant light buckets, they collect more light than our eyes can (larger collecting area). They can see more detail than our eyes can (better resolution). They can detect other forms of light, like x- rays, infrared, radio (better wavelength coverage).

40 Bigger is better! Collects more light

41 Bigger is better! Better angular resolution 0.15 m 0.50 m Ability to separate two nearby objects. 2.4 m 5.0 m

42 Basic Telescope Design Refracting: lenses Refracting Telescope Yerkes 1-m refractor

43 Basic Telescope Design Reflecting: mirrors Reflecting Telescope Gemini 8 meter

44 Tom Jarrett

45 Mauna Kea, HI

46 Twin 10-m Keck Telescopes

47 Using telecopes Astronomers almost never look through a telescope with their eyes. Instead instruments are used which are more sensitive, can see other wavelengths of light, and can record their data directly are used.

48 Radio Telescopes

49 Why do we put telescopes in space? We can over come problems with the Earth s atmosphere

50 1.) Light Pollution

51 1.) Light Pollution Bright Sky Dark Sky

52 2) Atmospheric Turbulence Atmospheric turbulence causes twinkling which blurs the image Limits the angular resolution of all big telescopes to about 0.5 arcseconds

53 2) Atmospheric Turbulence Image 1: From sea level (3 arcseconds) Image 2: From a mountain (0.5 arcseconds) Image 3: Hubble Space Telescope (0.1 arcseconds)

54 3) Atmospheric Absorption Most radiation is absorbed by the atmosphere (which is a good thing!)

55

56 Technology & Astronomy Adaptive optics: A fast computer figures how the atmosphere is distorting the light and moves a deformable mirror to compensate.

57 Technology & Astronomy Interferometry: allows individual telescopes to work together to achieve the angular resolution of a larger telescope.

58 Very Large Array (New Mexico)

59 Reminders Hand in Gratings before you go! HW #3 due in 1 week. Observing this week. Check website for weather updates. Read Chapter 10 for next time!