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.
Seeing
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 |
Summer Winter |
| Ozone | 180 mg/m³ | Max. |
| Wind | ||
| »Distribution | >10 m/s | 25% of the nights |
| >20 m/s | 50 nights per year | |
| Graph | ||
| »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 |