Site Details for Cerro Tololo and Cerro Pachon

The "El Totoral" Reserve, Cerro Tololo and Pachon

The Cerro Tololo Inter-American Observatory is located about 500km north of Santiago, Chile, about 52km ESE (80km by road) of La Serena, at an altitude of 2200 meters. It lies on a 34,491Ha (85,227 ac.) site known as "Estancia El Totoral" which was purchased by AURA on the open market in 1967 for use as an astronomical observatory.

When purchased, the land supported a number of subsistance farmers and goat herders. They were allowed to continue to live on the reserve after it was purchased by AURA and have gradually been leaving voluntarily for more lucrative jobs in the nearby towns.

As a result of departure of most of its human inhabitants and a policy combining environmental protection with "benign neglect" on the part of the Observatory, the property sees little human activity except for the roads and relatively small areas on the tops of Cerro Tololo and Cerro Pachon. As a result, much of the reserve is gradually returning to its natural state. Many native species of plants and animals, long thought in danger of extinction, are now returning. The last half of the trip to Tololo is an excellent opportunity to see a reasonably intact Chilean desert ecosystem. During the first portion of the journey, to a few km beyond "El Totoral", the effect on the environment of humans, bad farming practices and the remaining goats is easily seen. This damage will take many years to heal.

Sky Brightness over Cerro Pachon and Cerro Tololo

Light pollution from nearby cities (La Serena, Coquimbo, Ovalle, Andacollo, and Vicuna) has recently become a concern due to the rapid growth in population and development which this region of Chile has undergone. AURA and CTIO have undertaken an agressive campaign, both locally in the surrounding cities and at the Chilean congressional level, to alert the Chilean public and governing agencies to these concerns (e.g., CTIO's web page on light pollution at

However, it is not the current level of lighting which is worrisome. The concern is what changes the future development of the region will bring to what are presently extremely dark skies. A recent CTIO study, "Night Sky Brightness at Cerro Pachon" (at, presents the current numbers and several projections, depending on population growth and the success of lighting controls. The study demonstrates that with successful lighting awareness campaigns, such as that which CTIO/AURA has launched, Cerro Pachon and Cerro Tololo can continue to be prime astronomical sites far into the future.

The Top of Cerro Tololo

Roughly in the center of the property lies Cerro Tololo on which are located 5 working optical astronomical telescopes: The 4m Victor M. Blanco, 1.5m, .9m, the 1m Yale and the .6m Curtis-Schmidt telescopes.


Coordinates: W 70d48m52.7s S 30d09m55.5s

Telephone: 011-56-51-205200
Fax: 011-56-51-205212

Post: CTIO Support Office CTIO/AURA Inc.
      950 N. Cherry Ave.
      Tucson AZ 85719
    Observatorio Interamericano Cerro Tololo
    Casilla 603
    La Serena, Chile

Cerro Pachón

On the southeast side of the property lies Cerro Pachón where the new Southern Hemiphere Gemini 8m and the 4.2m SOAR telescopes are installed.

In this picture, looking up at the face of Pachón from the northwest, the Gemini dome can be seen. The SOAR site is behind the promontory in the top center of the picture.

CTIO/AURA La Serena Facilities

La Serena is a city with a population of over 100,000 about 490km North of Santiago, Chile at the mouth of the Elqui river.

 The CTIO facilities in La Serena support the Observatory and consist of instrument shops, engineering, operation and administration buildings along with visitor and staff lodging.

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