Paranal Site Information

The Paranal Observatory is located on the top of Cerro Paranal in the Atacama Desert in the northern part of Chile (map) and what is believed to be the driest area on Earth. Cerro Paranal is a 2,635-m high mountain, about 120 km south of the town of Antofagasta and 12 km inland from the Pacific Coast. The geographical coordinates are 24o 40' S, 70o 25' W.

The Paranal mountain was chosen because of its excellent atmospheric conditions and, not the least, its remoteness. This will ensure that the front-line astronomical observations to be carried out there will not be disturbed by adverse human activities, e.g. dust and light from roads and mines.

Below you will find some information about the geography and environment of the Paranal Observatory. The information include:

More details about the Environmental and Observing Conditions on the Paranal Observatory are presented in various papers and reports.

Observational Information

Photometric Nights

The sky is photometric in 78 % of the night time. Statistics of the photometric nights from 1984 onwards is available.


The 50 % fractile 0.66" FWHM. Seeing statistics from 1989 onwards is available.

Wind Velocity Distribution

The medium wind velocity at 10 M above the ground is 6.6 m/s. Statistics over the period October 1989 to June 1991 is available.

Water Vapour

The precipitable water vapour is less than 1 mm for 8.2 % of the night time. Curves showing the distribution of water vapour in the atmosphere above Paranal is available.

Geographical Information

Altitude above sea level 2635.43 m
Distance from coast 12 km
Highest neighboring peak Cerro la Chira, 2569 m, 11 km to the NNE
Road distances 130 km to Antofagasta
Appr. 1200 km to Santiago
Appr. 600 km to La Silla

Telescope number Latitude Longitude
UT1 -24deg 37 min 33.117 sec 70 deg 24 min 11.642 sec
UT2 -24deg 37 min 31.465 sec 70 deg 24 min 10.855 sec
UT3 -24deg 37 min 30.300 sec 70 deg 24 min 9.896 sec
UT4 -24deg 37 min 31.000 sec 70 deg 24 min 8.000 sec

Climate Information

Air pressure 750 mbar ±50 mbar
Density 0.96 kg/m³ Typ.
Temperature -8° to 25°C Measured 1985-1990
Temperature gradient during night -0.4°C/h Typ.
Typ. Humidity 5-20% Typ.
Rainfall <10 mm/year Typ.
Snow Once or twice per year Typ.
Ice buildup 5 cm Max.
Day/night averaged solar radiation Graph
Daily maximum 1120 W/m²
800 W/m²
Ozone 180 mg/m³ Max.
»Distribution >10 m/s 25% of the nights
  >20 m/s 50 nights per year
»Long term extremes 47.2 m/s 50 years return period
  50.7 m/s 100 years return period
  54.2 m/s 200 years return period
»Direction Wind rose
Pollution NO < 3 ppb Typ.
  NO2 < 2 ppb Typ.
  SO2 < 4 ppb Typ.

Seismical Information

Moderate earthquakes Some times per year Mg < 7.75
Operating basis earthquake (OBE):
»Peak horizontal acceleration 0.24 g Typ.
»Probability of excedance 50%
»Repetition period 25 years
»Magnitude 7.75 Richter
»Hypocentral distance 100 km
»Duration 65 s
Max. likely earthquake (MLE):
»Peak horizontal acceleration 0.34 g Typ.
»Probability of excedance 10 %
»Repetition period 100 years
»Magnitude 8.5 Richter
»Hypocentral distance 150 km
»Duration 200 s