University of Manitoba Astronomy Club

1. Special Club! • Contact: • umastroclub@gmail.com University of Manitoba Astronomy Club Wonder about the origins of the Universe? Curious about black holes? Come out and help design the club activities! No need to be a geek  Meeting Wednesday at 5:30 pm in Allen 330

2. 20,000° K 10,000° K 5000° K Intensity 2000° K 1000° K 500° K X-Ray Ultraviolet Visible Infrared Microwave Radio Phys 1830: Lecture 9 Tutorial/Office hour Today 3pm practice math and prepare for test. Test THIS Friday Jan 30th In class. See online handout. Includes telescopes (Wednesday’s material) • Change of password • Previous class: • Kirchhoff’s Laws • This class: • Spectra • How the interaction of light & matter produce spectra. • Optical Telescopes • Upcoming Topics • Radio Telescopes • B&W imaging workshop – scheduled Monday Feb 2 No more planetarium events. Contact Mr. Cameron.

3. Lecture 9: Telescopes -- Extending Vision • Next topics: • Optical Telescopes and detectors • Light gathering power • resolution • surface brightness • Radio Telescopes • 21 cm emission • Multiwavelength observations

4. Spectra Kirchhoff’s Laws summary Recall column • 3 empirical laws • Hot opaque body  continuous spectrum • Cooler transparent gas between source& observer  absorption line spectrum • Diffuse, transparent gas  emission line spectrum

5. Spectral Finger Prints Solar Spectrum • Note that the emission lines for the lab spectrum of iron are at the same wavelengths of the absorption lines of iron in the sun. • We can use line spectra to determine the chemical elements in an object.

6. Interaction of Light and Matter Creating spectral lines at visible wavelengths Absorption: • If the photon’s energy is not matched to any energy level then the photon passes by the atom. The atom is unchanged.

7. Interaction of Light and Matter Creating spectral lines at visible wavelengths Absorption: 2. If the photon’s energy matches the energy needed to cause an electron to jump to a larger energy level, then the atom absorbs the photon (i.e. absorbs energy) and the electron jumps to that energy level. The atom is now in an excited state.

8. Interaction of Light and Matter Creating spectral lines at visible wavelengths Absorption: 3. If the photon’s energy is larger than any jump within the atom, then the atom absorbs energy, the photon disappears, and an electron (or more) are kicked out of the atom creating an ion. (In an ion the charge is not balanced.) We say that the atom is ionized.

9. Interaction of Light and Matter • Eg. Iron absorption lines in the atmosphere of the sun. • Photons from the sun’s surface are absorbed by the gaseous iron atoms in the sun’s atmosphere. • The electrons at originally at those energy levels are kicked into excited or ionized states.

10. Interaction of Light and Matter Creating spectral lines at visible wavelengths Emission: • Photons can also be emitted spontaneously when an electron falls back down to lower energy levels. • An atom can be excited or ionized. An ejected electron can subsequently be recaptured. (animation)

11. Interaction of Light and Matter Creating spectral lines at visible wavelengths Emission: • These electrons can cascade through different energy levels, generating photons that have wavelengths in the visible regime. • The energy level in this example is called “H ” where is “alpha” and glows red – 656.3 nm.

12. Interaction of Light and Matter Creating spectral lines at visible wavelengths Emission: The Orion Nebula David Malin • Clouds of gas that glow due to this process have a few names: • Emission nebulae • H II regions • H regions • If they are very bright, they are pinker. • The ionizing photons come from hot stars.

13. Spectral Finger Print Hydrogen Atom Energy Levels • Each chemical element has its own “finger print” of lines. • The number of lines for one element depends only on the number of energy levels in its atom. • The more elements in a star, the more lines in the star’s spectrum.

14. Spectral Finger Print • The strength of the absorption lines gives the number of atoms of that element in the gas. • Comparison of strengths of absorption lines of different elements in the gas gives • Density • Temperature • Can get these characteristics for the outer layers of a star from its absorption line spectrum.

15. What can we do with this information? Study activity on the sun! • the Sun in extreme ultraviolet light (Solar Dynamics Observatory.) • false-color image shows emission from highly ionized iron atoms. • Loops and arcs trace the glowing plasma suspended in magnetic fields above solar active regions.

16. What can we do with this information? • (note asteroid trail in upper right corner) • Consider stars...

17. Spectral Finger Print • What can we do with this spectral information? • If 2 stars have the same elements, same density, and same temperature then they have the same intrinsic luminosity. • If they have the same intrinsic luminosity we can use their apparent brightnesses to derive their relative distances using the Inverse Square Brightness Law!

18. Spectral Finger Print • The uniqueness of the spectral line pattern of any element is caused by • The density of the gas in the stellar atmosphere. • The temperature of the gas in the stellar atmosphere. • The energy level structure of the atom.

19. Instrumentation for observing spectra: • To view spectra we use a spectrograph on a telescope. • Rather than using a prism, modern instruments use a diffraction grating to disperse the light.

20. Telescopes and Detectors:

21. What does a telescope really do? • gather light to see faint objects • focus the light to form an image or spectrum • resolves the image to see detail in the image

22. How does it do that? 2.4m 150mm Gathers light – depends on the size of the primary (main) mirror or lens in optical telescopes. Light Gathering Power (LGP) Therefore

23. LGP increases with the square of diameter of mirror/lens. Light Gathering Power summary Text Recall column Text smaller diameter larger diameter Digital Photography Photographic Plate

24. Charge-Coupled Device (CCD) summary Recall column • CCD replaced the Photographic Glass Plate as a recording medium (which in turn had replaced the eye as a detector) • similar to chip used in digital cameras but in astronomy we record in black and white. (More colour images coming up.)

25. Image Formation with optical telescopes double convex lens Refraction Reflection

26. Resolution – depends on the diameter of the mirror: summary Recall column -- If the angular resolution is small (i.e. fine), the resolution is high Low Resolution High Resolution  of mirror

27. If the angular resolution in an image is large then by definition the resolution of an image is high and one sees a lot of detail. • True • False

28. Talk to your neighbour about: • which are harder to build support structures for, mirrors or lenses? Why? • how does the diameter of the primary mirror effect the light gathering power and the resolution? • what is the relationship between angular resolution and resolution?

29. Review Question • Large reflector telescopes are better than medium-sized refractor telescopes because • They can collect more photons and hence show faint objects. • Telescopes with larger diameter mirrors show more detail within the field of view. • Mirrors are lighter than lenses and so reflecting telescopes need less support structure than refractors. • All of the above.

30. Telescopes: World’s largest Recall column Text • So is bigger, better? • Notice that they are all reflectors and built at high altitude. Why high altitude?

31. Atmospheric Transmission ionized gases N2,O2 H2O, CO2

32. Mountaintop Sites summary Recall column

33. Atmospheric Seeing – affects resolution! >1" Atmosphere limits what you can see in several ways κ Peg

34. Keck 1I 10m Adaptive Optics summary Recall column 1" 1.8m hex 0.3" Keck 1 10m Can achieve a mirror’s resolution in the near infra-red.

35. Why SpaceborneTelescopes? summary Recall column HST 2.4m

36. Orion transformed?

37. Above the atmosphere • Can observe at wavelengths that the Earth’s atmosphere blocks. Optical Far Infrared

38. Planck/Hershel and IRAS satellites:Far-Infrared (FIR)

39. Summary: - Resolution is affected by atmospheric seeing. - Atmospheric transmission filters electromagnetic radiation. summary Recall column

40. Resolution Revisited: When one doesn’t want high resolution. Kepler Mission’s “first light” image. • Why is this image of a globular cluster from NASA’s Kepler Mission fuzzy?

41. Resolution Revisited: When one doesn’t want high resolution. http://www.youtube.com/watch?v=dhQFOPtszRs • Kepler Mission is specifically is designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-size and smaller planets. • Primary mirror: 1.4 meter diameter • Wavelength range: 430-890 nm

42. Resolution Revisited: When one doesn’t want high resolution. • Spacebased photometry - measurement of amount of light • Light curves for stars to measure: • Transits of planets across the front of the star • Occultations of planets as they pass behind the star

43. Charge-Coupled Device for Optical Images • The number of photons per pixel are converted into electrons • each pixel can hold 65536 electrons • if there are too many photons from a bright star then there are too many electrons and they spill over into neighbouring pixels.

44. Resolution Revisited: When one doesn’t want high resolution. HST exposure of NGC 6791 • Bleeding or blooming from saturated pixels in bright stars. • Can avoid bleeding in lower resolution images.

45. Resolution Revisited: When one doesn’t want high resolution. Kepler Mission’s “first light” image. • Images of stars from NASA’s Kepler Mission are fuzzy so that stellar photometry can be measured accurately.

46. Review Question: • The Kepler Mission’s goals are to take the highest resolution images of stars as is possible in order to image planets encircling those stars. • True • False

47. Review Question: • Transit is when a smaller object passes behind a larger object. Occultation is when the smaller object is between the viewer and the larger object. • True • False