ASTRONOMY UNIT 4: LIGHT AND TELESCOPES Fall 2014 — Version 1.2 DUE ON: HW4-1 Mon 10/6 HW4-2 Thu 10/9 HW4-3 Fri 10/10 HW4-4 Tue 10/14 Read Seeds Ch. 6, intro and section 1; Supplemental Questions 1-7 (below); (125) Discussion Question 1 Read Seeds Ch. 6 section 2. We will be addressing all of these concepts, but not using the equations; Do (124) Review Questions 2, 3; (125) Learning to Look 2; Supplemental Questions 9-13 (below) Read Seeds Ch. 6 sections 3 through 6; (p124-125) RQ 4, 11; (125) Learning to Look 1; Supplemental Questions 14-17 Read Astronomy Reader Item 15 (page 25): “More Eyes on the Skies” Supplemental Questions 18-29 TEST: Wednesday, October 15th, 2014 — 3”×5” notecard allowed. SUPPLEMENTAL QUESTIONS 1. How do you see the black print on this white paper? Use the terms luminous and illuminated in your answer. 2. (a) Approximately how much energy (in eVs) is needed to break a water molecule? (b) Suppose you shine some very intense microwaves into some water. Could any one of those microwave photons break apart a water molecule? (c) Photons with the energy to break water molecules would be classified as what kind of light? (d) Look at Fig 6-3. Can any light with sufficient energy to break water get through our atmosphere? 3. I’m interested in studying black holes. (a) What kind of light should I look for? (b) Can I use a ground-based telescope or do I have to use a satellite? 4. Suppose an alien civilization is pointing a radio antenna at the Earth. Look at Fig. 6-3 on page 103 and comment on the strength of signal that they’ll get from FM or AM radio signals and old analog TV signals (UHF and VHF). 5. UHF stands for Ultra High Frequency. Compare the frequency of UHF to the frequency of regular visible light. Which is higher? 6. From your reading, what are the high and low ends of human vision, in terms of wavelength? 7. (a) From your reading, what is the altitude of the ozone layer? (b) If we were to have a huge hole in the ozone layer, how would that affect Fig 6-3? 8. Extra Credit: Use the figures on the “Working With Small Angles” page to derive the Small Angle Formula. (You need to use the fact that tan(θ) ≈ θ when θ is small and measured in radians. Give one or two examples θ and tan(θ) values to demonstrate the validity of this approximation.) 9. What is averted vision and what do you use it for? 10. About how long does it take to gain complete dark adaptation? 11. What color flashlight should you use to read a starchart while stargazing? Why? 12. How does increasing aperture affect light gathering power, angular resolution and magnification? 13. While out on a stargazing trip using a telescope an observer might encounter many problems (i through v). Match each problems with the most appropriate solution (A through E). Problems Solutions (i) I’m pointed directly at the right spot, but I (A) get a shorter eyepiece don’t see my faint object (B) get a longer eyepiece (ii) I have a big enough telescope, but my faint (C) get a larger telescope (increase aperture) object blends in with the grey sky. (D) go to a darker observing site (iii) My object seems too small. I want more (E) wait for a calmer night (or perhaps let your magnification. telescope equalize to air temperature) (iv) My object seems so big it doesn’t fit in my field of view. I want to see more of it. (v) My object seems all blurry, wavy or fuzzy. 14. Why can we observe in the infrared from high mountains and aircraft but must go into space to observe in the far ultraviolet? 15. What is (a) active optics and (b) adaptive optics? 16. Why is infrared or visible light interferometry much harder than radio interferometry? 17. Interferometry improves which? (a) angular resolution; (b) light gathering power; (c) magnification. 18. When was this article written? 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. (a) Where are the new telescopes being built? (b) When should they be finished? (a) What does E-ELT stand for? (b) Who’s building it? (c) How big will it be? (d) Where is it being built? (a) How big will the Giant Magellan Telescope be? (b) Where is it being built? (a) Where is the Thirty Meter Telescope being built? From 1948 to 1976, the Hale telescope was the world’s largest at 5.1 meters. The article alludes to a new construction technique allowing bigger, thinner mirrors that don’t sag. What is that technique? How do these new ground-based telescopes compare to the Hubble Space Telescope? (a) What kind of data will the Large Synoptic Survey Telescope collect? (b) How will it be used? NASA recently received two space telescopes from what unusual source? What’s a coronagraph, and how would it be useful? (a) How does the James Webb Space Telescope compare to the Hubble Space Telescope? (b) What problems has JWST faced? (c) When is it due for launch? (d) What kind of science will it do? How is the Hubble Space Telescope doing these days? REVIEW INFORMATION/QUESTIONS 1. You may prepare a 3” × 5” notecard for the test. Bring your calculator! 2. Know answers/how to do all the HW questions. 3. Look through the summary of Chapter 6 (p. 124). Make sure you know those terms that we’ve covered in class. 4. Know what changes you would have to make to a telescope to improve its light-gathering-power, angular resolution, and magnification. 5. Understand some about how eyes work, and how that relates to astronomy. What is dark adaptation? Why doesn’t red light effect it? What is averted vision? What about rods and cones makes averted vision work the way it does? 6. Also know the sequence from radio to gamma rays. (Which end is high frequency/low frequency? Which end is short wavelength/long wavelength? Which end is high energy/low energy?) 7. Know the wavelength range for visible light (400nm to 700nm). Which end is the red end, which end is the blue end? Would 350nm be UV or IR? Would 800nm be UV or IR? 8. Understand the transparency of the Earth’s atmosphere and how it affects astronomy. Why do we need satellites to see certain wavelengths? For what wavelengths are high, dry mountains most important? 9. What is a good angular resolution for human eyes? What is good angular resolution for a ground-based visible light telescope? 10. What is the biggest visible-light telescope? How big is it? Where is it? 11. Know where Aricebo is, where the VLA is, and where the VLT is. What does “VLA” stand for? What does "VLT" stand for? Know a little something about each of these telescopes. 12. Know why radio telescopes have to be so much bigger than visual telescopes. 13. Why does the HST have so much better resolution than most ground-based telescopes?