1. Midterm Distribution 31 A’s, 37 B’s, 26 C’s, 21 D’s, 17 F’s

2. Common Mistakes  Do the algebra first!  Units, Units, Units  Does your answer make sense?  Using ratios

3. Lecture 18: Telescopes and Observational Astronomy

4. There are two kinds of telescopes  Refracting  Refracting: a lens is used to focus the light from distant objects.  Reflecting  Reflecting: a primary mirror is used to gather and focus light.

5. A Refracting Telescope

6. A Reflecting Telescope

7. Alternative designs for reflecting telescopes

9. Charge Coupled Devices (CCD)

10. Fundamental Telescope Properties  Light collecting area (diameter of primary mirror or lens)  angular resolution (smallest angular distance that can be resolved clearly)  limited by effects of Earth’s atmosphere

11. Angular Separation  = 360 o. s /(2  d) “small angle formula”

12. Angular Resolution

13. Diffraction

14. The Diffraction Limit diffraction limit = 2.5 x 10 5 x wavelength of light (arcsec) diameter of telescope Find the diffraction limit of the 2.4 m Hubble Space Telescope for visible light (500 nm). d.l. = 2.5 x 10 5 (500 x 10 -9 m/2.4 m) = 0.05 arcsec

15. Where to put your telescope  high and dry – to minimize the blurring effects of the Earth’s atmosphere and emission/absorption from water vapor  away from light pollution  with roads, electricity, and other support systems nearby

16. The Summit of Mauna Kea

17. The Keck Telescopes

18. The Magellan Telescopes

19. Basic Functions of Telescopes  Imaging/photometry  accurate measurement of light intensity  filters can be used to separate into different colors  spectroscopy  light spread out using a diffraction grating  time sequence  how an object’s brightness changes with time

21. A Basic Spectrograph

22. Spectral Resolution

23. Telescopes across the spectrum

24. Hubble Space Telescope

25. Infra-red Telescopes SOFIA SIRTF

26. Radio Telescopes Arecibo Very Large Array (VLA)

27. Interferometry  An array of smaller telescopes can be used together  the light gathering power is equal to the sum of all the areas  the angular resolution is greatly improved

28. X-ray Telescopes grazing incidence mirror

29. Chandra X-ray Observatory

30. Compton Gamma-ray Observatory

31. Images of non-visible light

32. Radio CO FIR NIR vis. X-ray gamma ray