Telescopes and Astronomical Observations

1. Telescopes and Astronomical Observations Ay16 Lecture 5 Feb 14, 2008

2. Outline: What can we observe? Telescopes Optical, IR, Radio, High Energy ++ Limitations Angular resolution Spectroscopy Data Handling

3. A telescope is an instrument designed for the observation of remote objects and the collection of electromagnetic radiation. "Telescope" (from the Greek tele = 'far' and skopein = 'to look or see'; teleskopos = 'far-seeing') was a name invented in 1611 by Prince Frederick Sesi while watching a presentation of Galileo Galilei's instrument for viewing distant objects. "Telescope" can refer to a whole range of instruments operating in most regions of the electromagnetic spectrum.

4. Telescopes are “Tools” By themselves, most telescopes are not scientfically useful. They need yet other tools a.k.a. instruments.

5. What Can We Observe? Brightness (M) + dM/dt = Light Curves, Variability + dM/d = Spectrum or SED + dM/d/dt = Spectral Variability Position + d(,)/dt = Proper Motion + d2(,)/dt2 = Acceleration Polarization

6. “Instruments” • Flux detectors Photometers / Receivers • Imagers Cameras, array detectors • Spectrographs + Spectrometers “Spectrophotometer”

9. Aberrations • Spherical • Coma • Chromatic • Field Curvature • Astigmatism

10. Mt. Wilson& G. E. Hale 60-inch 1906 100-inch 1917

11. Edwin Hubble at the Palomar Schmidt Telescope circa 1950

13. Telescope Mirrors Multiple designs Solid Honeycomb Meniscus Segmented

19. Focal Plane Scale Scale is simply determined by the effective focal length “fl” of the telescope. = 206265”/fl(mm) arcsec/mm * Focal ratio is the ratio of the focal legnth to the diameter

20. Angular Resolution The resolving power of a telescope (or any optical system) depends on its size and on the wavelength at which you are working. The Rayleigh criterion is sin () = 1.22  /D where  is the angular resolution in Radians

21. Airy Diffraction Pattern * more complicated as more optics get added…

22. Encircled Energy Another way to look at this is to calculate how much energy is lost outside an aperture. For a typical telescope diameter D with a secondary mirror of diameter d, the excluded energy is x( r) ~ [5 r (1- d/D)] -1 where r is in units of  /D radians  a 20 inch telescope collects 99% of the light in 14 arcseconds

23. 2 Micron All-Sky Survey 3 Channel Camera

24. Silicon Arrays --- CCDs

25. CCD Operation Bucket Brigade

29. FAST Spectrograph

30. Simple Fiber fed Spectrograph

31. Hectospec (MMT)

32. Holmdel Horn

35. GBT

38. Astronomical Telescopes & Observations, continuedLecture 6 The Atmosphere Space Telescopes Telescopes of the Future Astronomical Data Reduction I.

40. Atmospheric transparency

42. Hubble

43. Ground vs Space

44. Adaptive Optics

46. Chandra X-Ray Obs

47. Grazing Incidence X-ray Optics Total External Reflection

48. X-Ray Reflection Snell’s Law sin11 =sin22 2/1=12 sin2 = sin1 /12 Critical angle = sin C = 12 --> total external reflection, not refraction

49. GLAST A Compton telecope

50. Compton Scattering