Chile’s Atacama Desert is one of the most famous astronomical sites on Earth.
It’s dark, its atmosphere is steady, dry and clear, and it’s home to some of the best ground-based astronomical infrastructure on the planet.
Atacama is the site of the European Southern Observatory’s Very Large Telescope and Very Large Array and, soon, will be home to an even bigger project: the Extremely Large Telescope.
As many of Earth’s darkest skies come under threat from light pollution, the name given to the negative effect of artificial light on our view of the heavens, you might think a region as pristinely dark, as astronomically important as Atacama would be safe.
Amazing Atacama astronomy
But not so, it seems.
We spoke to Astrophysicist Itziar de Gregorio-Monsalvo, the European Southern Observatory (ESO)’s representative in Chile, to find out more.
What makes the Atacama Desert a prime location for looking at the cosmos?
Chile is the best place on Earth for doing astronomy in different wavelengths.
We have very clear and quiet skies, which are perfect for observations in the optical and infrared.
We also have high, dry places in the mountains which are good for ‘millimeter’ and ‘submillimeter’ astronomy.
Observing sites like the European Southern Observatory (ESO) Paranal site are in the middle of the Atacama Desert, far from big cities and their associated light pollution.
What is light pollution?
It’s the brightening of the sky caused by the excess light that we human beings emit into the atmosphere.
We emit a large amount of unnecessary light – say, from poorly positioned streetlamps and the blue light component of LEDs – which can brighten the sky far away from the pollution’s source.
How does it affect astronomy?
It limits our ability to look deep into the Universe, particularly using optical astronomy.
When we observe with a telescope, we can’t differentiate light coming from the cosmos and light coming from light pollution.
So we can’t see very faint objects, such as Earth-like planets close to other stars.
What is threatening the quality of skies over ESO sites in Chile?
We’re being exposed to threats from industrial projects close to our Paranal observatories – huge projects, almost like mini cities, that require large amounts of light for safe operation.
One such project, INNA, which is a green hydrogen site, would sit very near the proposed south site of the Cherenkov Telescope Array Observatory (CTAO-South).
Could that have a wide impact at Paranal?
Yes. The blue photons that CTAO-South would observe are extremely sensitive to light pollution that we expect the INNA project will cause.
The project will also rely on a wind farm for energy, which is likely to shake the ground and cause vibrations that will impact the sensitive mirror alignment of the upcoming Extremely Large Telescope (ELT) and the interferometer VLTI.
The wind farm and solar plant will also contribute to increased atmospheric turbulence, which will be difficult to correct for and will damage the quality of our optical images.
That’s to say nothing of the construction phase and the associated dust and vibration.
What steps has ESO taken in response to the proposed project?
We’ve been calculating the impact of the INNA project and found that if they move to a safe distance away, the damage from vibrations and light pollution would be minimised.
We’ve submitted our proposals to the Chilean government as part of the project’s review process.
This will take time, but Chile is committed to protecting the quality of its dark skies – that’s been the case for more than six decades.
How is ESO tackling the wider challenges of light pollution?
ESO works with the regional government of Chile and collaborates with other international observatories to reduce light pollution.
We also raise awareness so that authorities and the public understand why they should protect the quality of the skies.
Why should we care about light pollution?
Dark skies are important for humanity because they’re the last windows into the Universe.
If you live in a big city, at some point you’ll no longer see the stars or the Milky Way. You’ll lose connection with the Universe.
On a practical level, the technology we use in astronomy also benefits humanity – take the digital camera, for example.
This progress will stop if we lose our power to observe the Universe.
How can people get involved?
It can start from very basic steps, like changing the lighting outside your house, through to more involved measures, like talking to your local government about what they’re doing to tackle light pollution.
This interview appeared in the September 2025 issue of BBC Sky at Night Magazine