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Modern Telescopes

Modern Telescopes. Lecture 12. Imaging Astronomy in 19c. In the old days, astronomers are using photographic plates (film on glass). Photography in 19c revolutionize the astronomy ability to collect light (photons) over long time = long exposures can see fainter object.

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Modern Telescopes

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  1. Modern Telescopes Lecture 12

  2. Imaging Astronomy in 19c In the old days, astronomers are using photographic plates (film on glass). • Photography in 19c revolutionize the astronomy • ability to collect light (photons) over long time = long exposures • can see fainter object. • film “catch” only 1 photons out of 50 incoming. Efficiency is about 2% • Charge-Coupled-Device (CCD) = digital camera  about 70% efficiency  images can be displayed on computer screen in real time.  “remote observation” : observing Keck telescopes in Hawaii from 1000s km away.

  3. Photometry • measurements of brightness of objects

  4. Large Synoptic Survey Telescope (8m) Camera • 1.6m by 3 m size • covers 3.5° field of view • 3600 Mega pixels • image the entire viewable sky every 2-3 nights • Produce about 15TB data evey night

  5. Spectroscopy Measuring spectra one of the most important usage of telescopes Spectrograph = a device that records spectra = diffraction grating + CCD diffraction pattern from CDs

  6. Two types of Spectra Absorption Spectrum Emission Spectrum

  7. Atmospheric Transmission • Because of the Earth Atmosphere, observations at Gamma-ray, X-ray, UV, far-infrared, long radio wavelengths should be done in space!

  8. Go beyond the atmosphere • SOFIA (Stratospheric Observatory For Infrared Astronomy) • 2.5m telescope in a flying Boeing 747! • Will fly at 41,000 feet (12km!).

  9. Radio telescopes • Using parabolic metal dish (reflecting antenna). • Molecules in space… (organic molecules!!) • Angular resolution in interferometry mode = two+ telescopes observing the same astronomical object resulting an angular resolution of a single telescope (whose diameter is equal to the baseline of two telescopes). Parkes telescope Australia, 64m

  10. Radio Astronomy Because of the diffraction limit of telescope (θ = λ / D), although radio telescopes are large (30-60 m), images taken at radio wavelengths are lower resolution. Map of Saturn taken with VLA at 2cm.

  11. Radio telescopes in interferometry mode • Very Large Array (VLA) : 27 antennae over ~20km arm. New Mexico

  12. Very Large Baseline Interfemetry • Radio telescopes over several continents • Compared to a single-dish radio telescope, VLBI can produce 10,000+ better resolution images.

  13. VLBI in space • Ground-based radio telescopes + radio telescope in Earth orbit

  14. Infrared Telescopes Orion in Optical Orion in Infrared

  15. Ultraviolet & Infrared Telescopes Spitzer IR telescope (85cm) Hubble telescope (2.4m)

  16. Non-optical wavelengths carry additional information!

  17. Next Generation Space Telescope • James Webb Space Telescope (JWST) • 6.5m telescope • Earth-trailing orbit

  18. X-ray Telescopes • Explore objects with temperatures of > 106 degrees • For example, Super-massive black-hole at M87 (nearby galaxy)

  19. European X-ray Telescope

  20. False-color images • SuperNova remnant (Supernova exploded 325 years ago) • Three space telescopes (X-ray : blue, Hubble: green, Spitzer: red)

  21. In summary… Important Concepts Important Terms Photometry Spectroscopy CCD • Atmospheric Windows • Multi-wavelength astronomy • Chapter/sections covered in this lecture : sections 6-4 through 6-7

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