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Astroclimatology of Paranal

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Seeing Conditions at Paranal

Seeing is defined as the image size (FWHM) in arcsec on a long exposure limited by the atmosphere (ie. telescope without optical aberrations nor dome/mirror seeing) as observed at zenith and at 0.5 micron. The seeing varies with the airmass to the power of 3/5th and with the wavelength to the power of -1/5th. The seeing is in principle, as long as the above criteria are fulfilled, independent of telescope diameter and the measurements by the differential image motion method (DIMM) fit well to all medium size telescope. For the recent family of diameter 8m and more however, the image quality appears better than predicted by DIMM because of a strong contribution of the surface layer below 30m (The Messenger no.132-jun08). Secondly, the science images are improving at long wavelength faster than the standard -0.2 lambda power law dependency (see the section on outer scale effects).
 * DIMM Seeing Monthly Averages graph (with historical milestones) and data since 1988 and since UT1 First Light
 * DIMM Seeing overall distribution and variability 1989-1995 and 1999-2003, photometric time.
 * DIMM Seeing and Wind Direction.
 * DIMM Seeing and Vertical Temperature gradient in the surface layer.
 * Chile Astroclimate update, and DIMM Seeing and El Niño
 * Atmospheric Parameters Relevant for Adaptive Optics
 * Outer Scale of the Turbulence and contribution of the Surface Layer to the seeing.

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