Modern Telescopes Lecture 12

Imaging Astronomy in 19c Photography in 19c revolutionize the astronomy 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 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. In the old days, astronomers are using photographic plates (film on glass).

Photometry measurements of brightness of objects measurements of brightness of objects

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

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

Two types of Spectra Absorption Spectrum Emission Spectrum

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

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

Radio telescopes Using parabolic metal dish (reflecting antenna). Using parabolic metal dish (reflecting antenna). Molecules in space… (organic molecules!!) 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). 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

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.

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

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

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

Infrared Telescopes Orion in Optical Orion in Infrared

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

Non-optical wavelengths carry additional information!

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

X-ray Telescopes Explore objects with temperatures of > 10 6 degrees Explore objects with temperatures of > 10 6 degrees For example, Super-massive black- hole at M87 (nearby galaxy) For example, Super-massive black- hole at M87 (nearby galaxy)

European X-ray Telescope

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

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