Site Description

Site Details for Cerro Tololo and Cerro Pachón

  "El Totoral" Reserve
  Sky Brightness
  Cerro Tololo
  Sidney Wolff view
  Cerro Pachón
  CTIO/AURA La Serena Facilities




The "El Totoral" Reserve, Cerro Tololo and Pachón

The Cerro Tololo Inter-American Observatory is located about 500km north of Santiago, Chile, about 52km EAST (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 Pachón. 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.


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Sky Brightness over Cerro Pachón 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)

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. The most recent published measurement of the sky over La Serena and Coquimbo, viewed from Cerro Tololo, are presented in Kriscuinas et al., 2010, PASP, 122, 373-377, "Light Pollution at hight zenith angles as measured at Cerro Tololo Inter-American Observatory" (see specially figures 1 and 3) and in Kriscuinas et al., 2007, PASP, 119, 687-696 "Optical sky brightness at Cerro Tololo Inter-American Observatory from 1992 to 2006".  A CTIO study in 2004, discussed predictions for night sky brightness at Cerro Pachón, un the context of planning for the LSST- presenting the relevant 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 Pachón and Cerro Tololo can continue to be prime astronomical sites far into the future.

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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 
Individual determinations of the geodetic positions for the observatories on Cerro Tololo and Cerro Pachon
Geodetic and geocentric positions and elevations for observatories on Cerro Tololo and Cerro Pachon (September 2012)

See google map here

Telephone: 011-56-51-225415
Fax: 011-56-51-205342

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

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Sidney Wolff view

View point from the road to Cerro Tololo in honor to Dr. Sidney Wolff. See the news article at NOAO

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Cerro Pachón

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

soar1_m.jpg In this picture, looking up at the face of Pachón from the northwest, the Gemini dome can be seen when it was under construction. The SOAR site is behind the promontory in the top center of the picture.
A broader look to Cerro Pachón years later (2011), where SOAR (left) and Gemini (right) can  easily  be distinguished.

Two bumps furthewr to the right of the Gemini SIte is where rock blasting preparation work on the site for the LSST is currently under way.

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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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