October 21, 2011 – 10am class

1. October 21, 2011 – 10am class Liberal Arts Minor in astronomy Watch email for Star Party news Turn in IR lab in front of room Orionid Meteor Shower Today: Telescopes, The Sun

2. The Liberal Arts Minor in Astronomy The Liberal Arts Minor in Astronomy is intended for undergraduate students of any field who wish to bolster their major concentration with a sustained study of astronomical concepts, history, and methodology. The Liberal Arts Minor in Astronomy may be added to any type of degree (e.g. B.A., B.F.A., B.S., etc.). The Liberal Arts Minor in Astronomy requires 18 units of Astronomy courses, of which 9 units must be upper division. Courses used to fulfill a General Education requirement cannot be used for the minor. Courses which can be used for the Liberal Arts Minor in Astronomy include: • ASTR 201 Cosmology • ASTR 202*Life in the Universe • ASTR 203 Stars • ASTR 204 Great Debates in Astronomy • PTYS 206 The Golden Age of Planetary Exploration • PTYS 214*Astrobiology: A Planetary Perspective • OPTI 200 Light, Color, and Vision Upper Division • ASTR 302 Introduction to Observational Astronomy [requires computing experience] • ASTR 320†Philosophy and History of Astronomical Thought • ASTR 333 Astronomy and the Arts • ASTR 345 Cultural Astronomy • ASTR 392 Directed Research [graded, 3 units may be used for the minor] • PHIL 305†Introduction to the Philosophy of Science *†can not receive credit for taking both of these courses

3. The Liberal Arts Minor in Astronomy • You can enroll in the Liberal Arts Astronomy Minor at your own college’s advising office. • If you have any questions about the minor, please contact Dr. Thomas A. Fleming: • Steward Observatory Room 209 • 621-5049 • taf@as.arizona.edu

4. Optical Light Telescopes: • Refracting (use a lens) • Reflecting (use a mirror) REFRACTING TELESCOPE: Examples Galileo’s telescope, our eyes A CONVEX lens (thick in the middle) focuses light to a point. • Light gathered • From a large • Area is • Concentrated • Can see fainter • Objects than you • Can with your eye

5. Objective Lens Eyepiece Lens Focal Length Objective Focal Length of Eyepiece Refracting Telescope Refracting Telescope:Lens focuses light onto the focal plane Focal length

6. Reflecting Telescopes: Use mirrors as the optics • A mirror shaped like a PARABOLA focuses light to a point. focus Light from a large area is concentrated in a small area.

7. Newton’s Telescope: The first reflecting telescope Secondary Mirror Primary Mirror

8. The world’s biggest telescopes are reflectors, not refractors. What’s wrong with lenses? Lenses absorb light. Lenses sag. Lenses have chromatic aberration: colors don’t focus at the same point.

9. Blue Focus Red Focus Chromatic Aberration. As light passes through a lens, just as a prism will disperse light, the lens will focus bluer wavelengths differently than the redder wavelengths.

10. World’s largest refracting telescope: Yerkes Observatory, D = 1 meter, completed In 1898.

11. Reflecting telescopes do not suffer from Chromatic Aberration. All wavelengths will reflect off the mirror in the same way. Reflecting telescopes can be made very large because the mirrored surfaces have plenty of support. Thus, reflecting telescopes can greatly increase in light gathering and resolving power. Reflecting telescopes are often cheaper ($$$) to make than similarly sized refracting telescopes.

12. Amount of light collected per second is is proportional to the AREA of the lens or mirror. D = diameter of lens/mirror

13. A bigger lens or mirror is able to resolve finer structures in the image low resolution high resolution Two stars are “RESOLVED” if they are seen as separate points.

14. Smallest angle resolved is proportional to 1/D where D = the diameter of the mirror MAGNIFICATION is not as important: Big, blurry image is less useful than small, sharp image.

15. A MODERN REFLECTING TELESCOPE: Large Binocular Telescope: Mt. Graham, near Safford AZ. Two mirrors, each 8.4m in diameter

16. Where to put a Telescope? Far away from civilization – to avoid light pollution

17. “Seeing” = twinkling Weather conditions and turbulence in the atmosphere set limits to the quality of astronomical images from ground-based observatories Mountain top observatories are put on peaks where the Atmospheric turbulence is minimal Bad seeing Good seeing

18. Laminar vs. Turbulent Fluid Flow Air becomes turbulent when it encounters a barrier – e.g. a mountaintop  bad seeing

21. The Hubble Space Telescopeis 600 kilometers above the Earth’s surface.

22. Hubble Space Telescope has great angular resolution; it’s above the turbulent atmosphere. Light-gathering ability? Not as great; it’s only D = 2.4 meters in diameter. Problem: It costs a lot of money to put a telescope in space!

23. Problem #2: It’s really hard to repair telescopes in space – only Hubble was designed to be repairable

24. X-Ray Astronomy X-rays are completely absorbed in the atmosphere. X-ray astronomy has to be done from satellites. NASA’s Chandra X-ray Observatory

25. Gamma-Ray Astronomy Gamma-rays: most energetic electromagnetic radiation; traces the most violent processes in the Universe The Compton Gamma-Ray Observatory

26. Infrared Astronomy Although short wavelength IR gets through the atmosphere, longer wavelength IR does not. In space, can cool the telescopes so it’s not a source of high background Spitzer Space Telescope Next Huge NASA mission, after Hubble Space Telescope ends: James Web Space Telescope (JWST)

27. Radio telescopes detect radio frequency radiation which is invisible to your eyes. Parabolic “dish” of a radio telescope acts as a mirror, reflecting radio waves to the focus.

28. Radio telescopes can be huge because they don’t have to be as smooth as optical telescopes: the wavelength of radio light is several cm’s and mirrors only have to be smooth to about 1/20 of a wavelength to focus the light well Surface of mirror

29. Arecibo Radio Observatory in Puerto Rico

30. Radio Interferometry The Very Large Array (VLA): 27 dishes are combined to simulate a large dish of 36 km in diameter. Even larger arrays consist of dishes spread out over the entire U.S. (VLBA = Very Long Baseline Array) or even the whole Earth (VLBI = Very Long Baseline Interferometry)