1. Class Update Observations Moon Phases Due Tuesday, Mar. 3 (2 weeks) Tuesday, Feb. 17 7:30-10pm Macalester College (Telescopes only) Friday, Feb. 20 8-9:30pm University of Minnesota (Telesc. & Star Gazing [no Moon]) Sunday, Feb. 22 7:30-10pm Macalester College (Telescopes, Moon Craters, & Star Gazing with Raquel) Grades updated yesterday, Feb. 16 Pick-up tests at end of lecture if you haven’t yet. Answers posted outside office. Question 46: B or D is correct. Please notify of Scantron mistakes before you leave. No class Thu, Feb. 26 for Student Success Day – Please attend

2. Astro News Rosetta spacecraft –First close images of Comet 67p (Churyumov- Gerasimenko) http://www.universetoday.com/118981/the-first-images-are- in-from-rosettas-valentines-day-comet-flyby/#more-118981http://www.universetoday.com/118981/the-first-images-are- in-from-rosettas-valentines-day-comet-flyby/#more-118981 –Comet 67p is outside Mars and will get closest to Sun in August (inside Mars orbit, outside Earth orbit) –Philae landing on Comet 67p in November –http://sci.esa.int/where_is_rosetta/http://sci.esa.int/where_is_rosetta/ Mars and Venus near Moon this week –Venus brighter than Mars

3. Spectra Radiation and Spectra Three types of spectra What we can learn from spectra

4. Part of the above from http://library.thinkquest.org/10380/advanced.shtmlhttp://library.thinkquest.org/10380/advanced.shtml <5% of universe Visible ROY G. BIV  Long λ (700 nm) (400 nm) Short λ  Low f High f Low energy High energy Electromagnetic (EM) Spectrum Ralph's Mother Is Visiting Uncle Xavier's Garden Radio Microwave Infrared Visible Ultraviolet X-ray Gamma

5. Electromagnetic (EM) Waves Gamma X-ray Ultraviolet Visible Infrared Microwave Radio Radar TV FM AM

6. Which type of EM wave is generated from radioactive materials? GAMMA RAYS or gamma radiation Gamma rays are used in medical PET scans. Most gamma rays are generated from universe. Radar TV FM AM

7. Which type of EM wave is used to look at human bones? X-RAYS X-rays are used in airport security. X-rays are emitted from hot gases in the universe. Radar TV FM AM

8. Which type of EM wave causes sunburn, skin cancer, cataracts? Radar TV FM AM ULTRAVIOLET From “hot” objects in space (Sun and stars)

9. Which type of EM wave can you see? VISIBLE Radar TV FM AM From fireflies, light bulbs and stars

10. Which type of EM wave feels warm? INFRARED Radar TV FM AM From our bodies and objects with heat Used in TV remote controls and night vision goggles Penetrates smoke and dust Helps map dust between stars

11. Which type of EM wave warms food? MICROWAVES Radar TV FM AM Used to learn about the structure of nearby galaxies

12. Which type of EM wave can you play on your car stereo? RADIO Radar TV FM AM Frequency of most wireless devices From stars and gases

13. Electromagnetic (EM) Waves Radar TV FM AM < 5 % of universe

14. ALL EM WAVES: Travel through the vacuum of space (sound cannot) Travel at the speed of light through the vacuum of space

15. ALL EM WAVES Differ in: λ f Energy Temperature

16. Earth’s atmosphere absorbs most EM waves http://www.ipac.caltech.edu/outreach/Edu/Windows/irwindows.html

17. Spectra DR21 6000 ly 75 ly Cygnus Looking with “other eyes” Ex: Newborn stars (IR)

18. Spectra Visible Infrared

19. 938 nm, 889 nm, 420 nm Green – surface Red – high atm, methane absorbs sunlight Blue – violet wavelengths for the haze Near IR 938 nmComposite visible Titan (moon of Saturn) – NASA/JPL

20. To detect an EXTREMELY ENERGETIC event like two neutron stars merging, “look” for this kind of wave: 1. Radio 2. Micro 3. IR 4. Visible 5. UV 6. X-ray 7. Gamma

21. To detect a VERY LOW ENERGY event like the spin flip of a H atom, “look” for this kind of wave: 1. Radio 2. Micro 3. IR 4. Visible 5. UV 6. X-ray 7. Gamma

22. Spectra **Waves carry energy, hence, information. λ (or color) tells you… Temperature Ex: Star color tells you hot star or cool star

23. Spectra From last lecture: Spectrum – display of color or wavelengths Spectra – plural

24. Wave Properties (Previous Lecture) 1. Speed 2. Wavelength 3. Frequency 4. Energy

25. What can we learn from spectra? 1. Temperature - from color (last lecture) 2. 3. 4.

26. What can we learn from spectra? 1. Temperature - from color (last lecture) https://docs.kde.org/stable/en/kdeedu/kstars/ai-colorandtemp.html

27. What can we learn from spectra? 1. Temperature - from color (last lecture) https://docs.kde.org/stable/en/kdeedu/kstars/ai-colorandtemp.html

28. What can we learn from spectra? 1. Temperature - from color (last lecture) 2. Composition - from spectra lines 3. 4.

29. Spectra Diffraction Grating –Spreads out the wavelengths –Uses parallel lines to split and diffract light –Same spectrum on both sides –Ex: Show light bulb spectrum (handout)

30. Spectra Continuous Emission Absorption Three Types of Spectra Combinations

31. Spectra Types of Spectra Continuous, Emission, Absorption Describe:

32. Spectra Types of Spectra Continuous, Emission, Absorption Describe: Rainbow like, all λ

33. Spectra Types of Spectra Continuous, Emission, Absorption Describe: Rainbow like, all λ Source: Hot, dense object

34. Spectra Types of Spectra Continuous, Emission, Absorption Describe: Rainbow like, all λ Source: Hot, dense object Ex: Filament of light bulb, surface of star

35. Types of Spectra Continuous, Emission, Absorption Describe:

36. Types of Spectra Continuous, Emission, Absorption Describe: Bright lines

37. Types of Spectra Continuous, Emission, Absorption Describe: Bright lines Source:

38. Types of Spectra Continuous, Emission, Absorption Describe: Bright lines Source: Excited gas Ex: gas tube gas clouds in space

39. Spectra Emission Spectra Compare spectrum of H to He H spectrum is different than He spectrum http://pixgood.com/helium-absorption-spectrum.html

40. Spectra Emission Spectra Each element has a unique spectrum. Different gases have different spectra. Now know composition of stars!!!

41. Types of Spectra Continuous, Emission, Absorption Describe: Emission Absorption

42. Types of Spectra Continuous, Emission, Absorption Describe: Dark lines Missing colors Missing λ Continuous with missing λ

43. Types of Spectra Continuous, Emission, Absorption Describe: Dark lines Source:

44. Types of Spectra Continuous, Emission, Absorption Describe: Dark lines Source: White light shining through a gas or liquid i.e. Light from a hot dense object shining through a gas or liquid

45. What can we learn from spectra? 1.Temperature (from color) 2.Composition (from spectra lines) 3.Density (from spectra type) = mass/volume –Continuous (rainbow) –Emission (bright lines) –Absorption (dark lines) 4.

46. Spectra What can we learn from EM spectra? 1.Temperature 2. 3. 4. Composition Density http://www.jb.man.ac.uk/astronomy/nightsky/AList/Albireo.jpg http://astro.unl.edu/naap/hr/hr_bac kground1.html

47. Hot Dense Object

48. Same lines

49. What can we learn from spectra? Density (from spectra type) = mass/volume –Continuous (rainbow) From a hot, dense object –Emission (bright lines) From a gas cloud –Absorption (dark lines) From a hot, dense object through a gas cloud

50. Spectrum of our sun What type of spectrum? What does that tell you about our sun? ABSORPTION SUN VIEWED THROUGH GAS CLOUD (Sun’s atmosphere acts as a gas cloud)

51. Spectra Next time Blackbody radiation Why lines in the spectra at all? What do those lines mean? Annie Cannon, Cecilia Payne

52. What can we learn from spectra? 1.Temperature (from color) 2.Composition (from spectra lines) 3.Density (from type) 4.Motion (from spectra shift) Doppler Shift lecture coming up