Landmark South America
La Silla Observatory
La Silla Observatory is a group of telescopes on a mountain in Chile. The night sky there is very dark, so the stars look bright!
La Silla Observatory sits 2,400 meters up on a mountain at the edge of Chile's Atacama Desert, about 600 kilometers north of Santiago. It was the first observatory of ESO, the European Southern Observatory, and its telescopes have studied stars, planets and exploding stars since the 1960s.
La Silla, at 2,400 m on the outskirts of the Atacama Desert, was the European Southern Observatory's first observatory: building began in 1965 and the site was inaugurated in 1969. Far from light pollution, it has one of the darkest night skies on Earth. ESO runs two 4-meter-class telescopes there, the New Technology Telescope and the ESO 3.6-meter telescope with the planet-hunting HARPS spectrograph.
Photo: Cfoellmi~commonswiki, CC BY 2.5, via Wikimedia Commons
Discover La Silla
La Silla is in Chile, a long, thin country in South America.
Its telescopes sit in white domes on top of a dry mountain.
La Silla Observatory stands 2,400 meters high at the edge of the Atacama Desert, 600 kilometers north of Chile's capital, Santiago.
It is far from city lights, and ESO says it has one of the darkest night skies on Earth. ESO has run telescopes here since the 1960s.
ESO describes La Silla as its first observatory, on the outskirts of the Chilean Atacama Desert, 600 km north of Santiago de Chile and at 2,400 m. Like other observatories in the area it lies far from sources of light pollution, and ESO says it has one of the darkest night skies on Earth.
Besides ESO's own telescopes, its infrastructure serves projects of ESO's member states, such as the BlackGEM and ExTrA telescopes and the MPG/ESO 2.2-meter telescope.
- Where
- Edge of the Atacama Desert, Chile
- Altitude
- 2,400 m
- From Santiago
- 600 km north
- Run by
- ESO (European Southern Observatory)
ESO's first observatory
Long ago, scientists from Europe chose this mountain for their telescopes.
The first telescope here began looking at the sky in 1966.
In 1964 ESO chose a mountain called Cinchado Nord, later named La Silla, for its observatory. Building began in March 1965.
The first ESO telescope in Chile, a 1-meter telescope, saw its first light in November 1966. The site was officially opened in 1969, and a bigger telescope, with a mirror 3.6 meters across, followed in 1976.
ESO's timeline records that on 26 May 1964 the ESO Council selected the mountain Cinchado Nord, later La Silla, as its observatory site; the land was acquired that October, and construction began in March 1965.
On 30 November 1966 the ESO 1-meter telescope saw first light, the first telescope ESO used in Chile. The site was inaugurated on 25 March 1969, and the ESO 3.6-meter telescope saw first light on 7 November 1976.
A mirror controlled by a computer
One telescope here has a mirror that a computer keeps in the right shape.
Many big telescopes now use this idea.
ESO's two main telescopes at La Silla are both in the 4-meter class. The New Technology Telescope, with a mirror 3.58 meters across, was the first in the world with a main mirror controlled by a computer.
This idea, called active optics, was developed at ESO and is now used by most of the world's large telescopes.
ESO operates two of what it calls the most productive 4-meter-class telescopes in the world at La Silla. The 3.58-meter New Technology Telescope (NTT) broke new ground in telescope engineering and design: it was the first in the world with a computer-controlled main mirror.
That technique, active optics, was developed at ESO and is now applied to most of the world's current large telescopes. La Silla was also the first world-class observatory certified under the ISO 9001 quality management standard.
Hunting for planets
A special instrument here helps scientists find planets around other stars.
It found planets going around the star closest to the Sun!
The ESO 3.6-meter telescope carries HARPS, an instrument that ESO calls the world's foremost planet hunter. It has found planets around Proxima Centauri, the star closest to the Sun.
Telescopes at La Silla also helped study gamma-ray bursts and the nearby supernova SN 1987A, an exploding star. Studies of exploding stars, partly made here, showed that the Universe's growth is speeding up.
HARPS (the High Accuracy Radial velocity Planet Searcher), on the ESO 3.6-meter telescope since 2003, is in ESO's words the world's foremost extrasolar planet hunter; its finds include the first rocky exoplanet in the habitable zone of its star and planets orbiting Proxima Centauri.
La Silla telescopes also played a key role in gamma-ray burst research and in following SN 1987A. Observations of exploding stars partly made at La Silla fed the 1998 discovery that the Universe's expansion is accelerating, which won the 2011 Nobel Prize in Physics.
- First ESO telescope in Chile
- 1966
- Site inaugurated
- 25 March 1969
- HARPS first light
- 2003
Domes on the ridge
In this photo, tiny white domes line the top of a long, dark mountain.
Low sunlight makes the hills in front glow orange.
This photo was taken on 17 April 2005 from the road to another observatory, Las Campanas. White telescope domes and buildings line the ridge of La Silla, with a large dome on the left.
In front, rounded desert hills glow orange in low sunlight. Visitors can tour La Silla on some weekends.
The photograph (17 April 2005), taken from the road to the Las Campanas Observatory, shows La Silla's summit ridge in profile: a large dome on the left peak, a line of smaller domes and buildings along the crest, and in the foreground bare desert hills lit by low sun.
ESO's site lists weekend visits for the public. In 2019 La Silla marked its 50th anniversary with a total solar eclipse.
Amazing facts
-
The mountain had a different name before the observatory came!
When ESO chose the mountain in 1964, it was called Cinchado Nord. It later became La Silla.
The ESO Council selected the mountain Cinchado Nord, later to become La Silla, on 26 May 1964.
-
A telescope here helped find planets around the star closest to the Sun!
HARPS, on the ESO 3.6-meter telescope, helped find planets orbiting Proxima Centauri, the closest star to the Sun.
HARPS's finds include the first rocky exoplanet in its star's habitable zone and planets orbiting Proxima Centauri.
-
On La Silla's 50th birthday, the Moon hid the Sun!
In 2019, La Silla's 50th anniversary came with a total solar eclipse.
ESO's timeline pairs La Silla's 50th anniversary on 3 July 2019 with a total solar eclipse.
Words to know
- observatory
- a place with telescopes for studying the sky
- telescope
- an instrument that collects light to see faraway things
- first light
- the first time a new telescope looks at the sky
- light pollution
- light from towns and cities that brightens the night sky
- exoplanet
- a planet that goes around a star other than the Sun
- active optics
- a computer system that keeps a telescope's mirror in the right shape
Discovery challenge
-
In which country is La Silla Observatory?
La Silla Observatory is 600 kilometers north of the capital of which country?
On the outskirts of which country's Atacama Desert is La Silla?
- Chile
- Spain
- Kenya
Show the answer
Chile
Chile!
Chile (its capital is Santiago).
Chile.
-
Why are telescopes built far from cities?
Why is La Silla's location good for looking at faint stars?
What does ESO say La Silla's remote site keeps it far from?
- City lights
- The ocean
- Snow
Show the answer
City lights
City lights make the sky too bright!
It is far from city lights, so its night sky is very dark.
Sources of light pollution.
-
How high up is La Silla?
At what altitude is La Silla Observatory?
What altitude does ESO give for La Silla?
- 2,400 meters
- 240 meters
- 24,000 meters
Show the answer
2,400 meters
2,400 meters!
2,400 meters.
2,400 m.
-
What does the instrument HARPS look for?
What does HARPS, on the ESO 3.6-meter telescope, hunt for?
ESO calls HARPS the world's foremost hunter of what?
- Planets around other stars
- Comets in the ocean
- Clouds on Earth
Show the answer
Planets around other stars
Planets around other stars!
Planets around other stars, called exoplanets.
Extrasolar planets.
-
When did the first telescope here start looking at the sky?
In which year did the first ESO telescope in Chile see first light at La Silla?
In which year did the ESO 1-meter telescope, ESO's first telescope in Chile, see first light?
- 1966
- 1906
- 1996
Show the answer
1966
1966!
1966.
1966 (30 November).
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For parents & teachers
What children will learn
- Explain why observatories are built on high, dry mountains far from cities.
- Describe what a telescope mirror does.
- Explain how scientists can find planets around other stars.
Recommended ages: 4 to 17 · About 15 minutes
Talk about it
- How does light from cities change what we can see in the night sky?
- Why might a telescope mirror need a computer to keep its shape?
- If you could point a telescope anywhere, what would you look at?
Try at home or in class
- On a clear night, count the stars you can see in town, then count again somewhere darker.
- Find the Atacama Desert and Santiago on a map of Chile.
Key vocabulary: observatory, telescope, first light, light pollution, exoplanet, active optics
Where these facts come from
- Wikidata , Wikimedia Foundation (CC0 1.0)
- La Silla Observatory , ESO (European Southern Observatory)
- ESO Timeline , ESO (European Southern Observatory)
- File:Observatoire de LaSilla depuis la route de Las Campanas.jpg , Wikimedia Commons
- Wikimedia Commons , Wikimedia Foundation (Per file (public domain, CC0, CC BY or CC BY-SA); see each media record)
Checked, not yet human-reviewed. Last updated November 1, 2026. Spotted a mistake? Tell us.