Telescopes, Optical

Keywords history of astonomy, refractors, optical telescopes... 

Independent arrays of telescopes have been discussed for decades but have generally not been successful, except for radio telescopes, where interferometry is a key virtue, aided by the fact that the individual telescope signals can be amplihed and combined while preserving phase information. This is not practical in the optical, thus there are significant inefficiencies in sensitivity by coherently combining the light from an array of optical telescopes. Instrumentation for an array of telescopes has also been a cause of difficulty. Perhaps the best known successful array has been the VLT with four 8-m telescopes, each with its own suite of science instruments, and the capacity to combine all telescopes together for Interferometric measurements. 

Ardeberg, A., Andersen, T., Lindberg, B., Owner-Petersen, M., Korhonen, T., Spnderg d, R, 1992, Breaking the 8m Barrier - One Approach for a 25m Class Optical Telescope, ESO Conf. 42, 75 Assus, P. et al, 1994, Performance and potential applications of replica technology up to the 1-m range, SPIE 2199, 870... 

OPTICAL FABRICATION FOR THE NEXT GENERATION OPTICAL TELESCOPES, TERRESTRIAL AND SPACE... 

Keywords optical telescopes, off axisaspheres, polishing methods... 

Optical Testing for theNext Generation Optical Telescopes... 

Courtgs, G. 1982, in Instrumentation for Astronomy with Large Optical Telescope, Proc. lAU Colloq 67, Astrophysics and Space Science Library 92, pl23. ed. Humphries, C.M., Dordrecht, Reidel Dubbeldam, C.M., et al., 2000, SPIE 4008, 1181... 

Next steps toward experimental works will be particularly exciting the MCAO MAD bench at ESO, the MCAO+LGSs device at Gemini South, experiments at the MMT and at Mt Wilson, the polychromatic LGS demonstrator in France. Also we still have a lot to learn with the feedback from the devices running now or very shortly, at Lick, Keck and ESO. But the biggest challenge of the coming years wdl be to extrapolate this know how to the case of decametric or even hectometric optical telescopes. 

Roddier, C., Roddier, R, 1993, Wave-front reconstruction from defocused images and the testing of ground-based optical telescopes, JOSA.A 10, 2277 (1993). 

We have observed three subgiants HD 23249 (KO), HD 198149 (KO), HD 222404 (Kl) and three dwarfs HD 10780 (KO), HD 4628 (K2), HD 201091 (K5), on 2002 November 28 and 29, with the high-resolution cross-dispersed echelle spectrograph SOFIN, mounted on the Nordic Optical Telescope (NOT). They are in the solar neighbourhood (< 15 pc), are very bright (V < 6) and have modest projected rotational velocities (v sin i < 4 km s 1) to limit blends between spectral lines. They also do not present any evidence for emission (or a moderate one, as in the case of the three dwarfs) in the core of Ca II H and K lines. 

Nordic Optical Telescope Scientific Association, Apartado 474,... 

In terms of directionality, an off-the-shelf laser may have a beam divergence of 0.5 milliradians. Such a laser, shone on the moon from the surface of Earth, would project a spot approximately 120 miles in diameter. Very special optics, e.g. colli-mation of the laser beam by a large optical telescope, can decrease the beam divergence by a factor of ten. 

Running in parallel to spectacular space-based astronomy, optical telescopes and radiotelescopes have progressed in a quite breathtaking manner thanks to the new techniques of interferometry and active and adaptive optics. Telescopes perched on mountain peaks, such as the CFHT (Canada-France-Hawaii Telescope) and Keck on Mauna Kea in Hawaii and the VLT on Cerro Parana in Chile, and radiotelescopes set out like windmills in Puerto Rico, Sologne (in the French Alps), The Netherlands and Spain, gather photons able to cross the layers of the atmosphere without major alteration, whilst spectrographs then dissect the radiation into its finest detail. 

Optical telescopes with 4 m diameter which had blossomed in many of the world s deserts have now been superseded by the space telescope and 8-m or 10-m telescopes on dry mountain peaks. These giants with their penetrating eye and minuscule field of view are mainly devoted to spectroscopy. 

American astronomy holds several trump cards. Until recently, its great optical telescopes, the HST and the twin telescopes Keck I and II set up on Manna Kea in Hawaii, reigned imperially over the visible and near UV sky. Although the European VET has largely counterbalanced this domination, the USA is ready to step into the lead once more. 

The spiral arms of the Milky Way are composed mostly of hydrogen. Except for the stars within these spiral arms, these spiral arms themselves are invisible to optical telescopes. The 21-cm line of hydrogen makes structural details of these spiral arms visible. Radio antenna tuned to this line can be swept across the disk of the Milky Way so that its spiral-armed structure can be observed. One such image constructed from hydrogen data was created by Gart Westerhout. It shows structural details of our galaxy (see Figure 17.3). ... 

What is in the nucleus of the Milky Way If we look with optical telescopes, we see nothing. The interstellar dust obscures the optical light. The center of the Milky Way does, however contain very strong sources of radio waves, infrared light, and x rays. One such source, called Sagittarius A", appears to lie at the precise center of the galaxy, the point about which the entire system rotates. 

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