Candidate Observatory Site:
Las Companas, Northern Chile


29 0 54 S, 70 41 32 W
(Copy and paste this location into or for images and maps of site.)


2500 meters (8200 feet)

Site Description

This site is located on a ridge in the front range of the Andes Mountains of northern Chile. It is a medium elevation site about 50 miles east of the Pacific Ocean. It is a developed site with several observatories already on the ridge (offices in La Serena, abut 70 miles to the southwest), so much of the infrastructure required for a new observatory already exists. Only a short piece of road would have to be constructed to the site.

Site Images

Las Campanas Panoramic image
View of the Las Campanas ridge from the approach highway, showing typical vegetation and surrounding terrain. Click image for full size view. Las Campanas Observatory image.

Las Campanas Ridge
View of the Las Campanas ridge , showing, from left to right, the du Pont, Swope, and twin Magellan telescopes. Photo by Krzysztof Ulaczyk, Las Campanas Observatory.


This is a dry site, located at the southern end of the Atacama Desert, the driest in the world.

Site Testing Information


Median seeing at Las Campanas is 0.6 – 0.7 seconds of arc with about 50% of the seeing between 0.4 and 0.8 seconds of arc.

To examine seeing data for individual nights at Las Campanas, visit:

Click on “Las Campanas seeing” on toolbar. Here is the seeing record for a randomly chosen night on Las Campanas:

poor seeing
On this night, seeing is poor at the beginning of the evening, but becomes world-class (0.4 seconds of arc) about halfway through the night.

Clear Nights.

Data on the number of clear nights in the vicinity of the Las Campanas site have been collected for nearly 40 years. Typically, the fraction of photometric nights is 60 – 65%, with 85% of the potential observing time being useful.

clear nights
Graph of clear nights from 1983 through 2007 over La Silla, an observatory close to Las Campanas. The average is 62%, with significant variability from month to month. Graph from

To examine cloudiness data for individual nights at Las Campanas, visit:

Click on “Cloudiness Calendar” on toolbar.

Precipitable Water

The test data for 29 clear nights in the southern winter of 2005 gave a median of 2:8 with an uncertainty of 0:3mm. (Data from J. E. Thomas-Osip of the Carnegie Institute of Washington, Las Campanas Observatory, Colina El Pino, Casilla 601, La Serena, Chile.)

Additional Information.

Other data (temperature, winds, etc.) for individual nights at Las Campanas, visit:

Select from the menu toolbar at left for desired information.