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.
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.
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.
| 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 |
| 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. | |
| 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 |
