Prime Dark Sites for the "100-club" Telescopes (100-inches to 100m primary mirrors).

 Class AClass BClass C sites are dark, or fairly dark sites where substantial investment has been made or will very soon be made in the construction of substantial, active, professional, ground-based, optical, research observatories.  No man-made light pollution has yet been detected in broad-band observations near the zenith at Class "A" and Class "B" sites (see, e.g., Patat, F. 2003, Astronomy and Astrophysics, 400, 1183). These dark sites are also where large telescopes (of equivalent aperture of at least 6.5m) are presently sited (Class "A") or where construction of such large telescopes has been funded (class "B").  Class "C" sites have either detected light pollution at the zenith, or are ones where no large telescopes (aperture ~6.5m or greater) are currently planned.  Thus, for example, Cerro Pachon is a "Class A" site; it is still dark at the zenith (the setting zodiacal light is readily visible over the direction of maximum horizon glow) and the Gemini South 8m telescope is on the summit.  Cerro Tololo, though only a few kilometers away and still dark, is a "Class C" site, because no telescopes larger than the Blanco 4m are currently planned for Cerro Tololo.

A. Sites for telescopes with mirrors already on site, aperture >6.5m, undetected light pollution at zenith.

Hawai'i, USA

Mauna Kea ( Keck I & 2; SubaruGemini North. UKIRTCFHT , IRTF).  See also John MacDonald's excellent web page on the "Light Environment of Mauna Kea".

Northern Chile (11MB, slow download)

 Cerro Paranal (VLT/VLTI, VISTA, VST)  This is in the clearest region of Chile, near the coast (67-68degW, 23-25degS).  This area is our Working Group's highest priority for protection against light pollution.  Intense outreach activity (18MB, slow download) by the OPCC is underway, concentrating initially on Antofagasta and on mines in the area (particularly PCS Yumbes).  Ferdinando Patat has published an excellent summary of the "Night Sky Brightness During Sunspot Maximum at Paranal" in the ESO "Messenger" (No. 115 - March  2004).   This  provides a valuable, quantitative benchmark  for dark skies work and a reference point for the protection campaign in Northern Chile over the next few decades.   More details of these measurements at Paranal are given in Patat, F. 2003a, Astronomy & Astrophysics, 400, 1183.  Information on the algorithm used for his measurements is given in Patat, F. 2003b, Astronomy & Astrophysics, 401, 797.

Cerro Las Campanas Cerro Las Campanas (Magellan I & 2, DuPont) .

Cerro Pachon ( Gemini South, SOAR). ( LSST - next decade).

South Africa

Sutherland Observing Station (10.2m Southern African Large Telescope, SALT).

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West Texas, USA

Mount Locke ( 9.2m HET ,  2.7m Harlan J. Smith telescope).  Visit StarDate Online to get to know an outstanding public outreach and education program.

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B. Other sites for telescopes being planned or built, apertures >6.5m, undetected light pollution at zenith.

Canary Islands

Roque de los Muchachos (GranTCan, WHT, INT, NOT).  Visit the OTPC ( english ) or ( spanish ) light pollution site, or contact Francisco Javier Diaz-Castro, a member of this WG.  See also the recent paper by M. Pedani on "Light pollution at the Roque de los Muchachos Observatory".

 C. Other major observatory sites with operating telescopes having apertures >2.5m & zenith light pollution levels less than the natural variation in night-sky brightness associated with the 11-year solar cycle.


 Siding Spring  ( 3.9m AAT)

Arizona, USA

Mount Hopkins ( MMT )

 Mount Graham (site for the  LBT )

 Kitt Peak National Observatory (Mayall 3.9m,  WIYN 3.5m; see "The Spectrum of the Night Sky over Mount Hopkins and Kitt Peak: Changes after a decade" - Publications of the Astronomical Society of the Pacific, Vol. 112, pp566-573, 2000 -  to see a remarkable success story in controlling light pollution and waste).

California, USA

Mount  Palomar (5m).  (See also the excellent LightLynx site).

Northern Chile

 La Silla (ESO 3.6m, 3.6m NTT)

Cerro Tololo (Blanco 4.0m)  A movie of Tololo's dark sky is included in Tom Lucas' production, for "NOVA" on PBS entitled "Runaway Universe".  Cerro Tololo is the most threatened of the major international observatories in Northern Chile but still has no detected light pollution at the zenith (the setting zodiacal light is readily visible over the direction of maximum city glow) - it is, however, vital that Chilean authorities continue implementing  the massive lighting changes required under the "Norma Luminica" DS686 as the nearby communities continue to grow.   Action on lighting changeover is underway in the various communities and provides a unique opportunity for ground-based and satellite monitoring.

New Mexico, USA

Apache Point Observatory,  APO ( ARC 3.5m telescope, SDSS telescope)


 Calar Alto (3.5m telescope)

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Light pollution is, of course, only one of many criteria that form the basis for site selection.  Other parameters may include atmospheric turbulence, cloud cover, precipitable water vapour, thermal emission from the atmosphere, auroral activity, aerosol/dust pollution, average and maximum wind speeds, seismic activity, rates of snow/rain fall, accessibility, infrastructure and cost of operation (see, e.g., Lawrence et al. 2004, Nature, 431, 278).

Last revised: 17th May, 2006