Light air pollution is threatening the darkest skies on Earth. This is how astronomers are preventing again

Chile’s Atacama Desert is without doubt one of the most well-known astronomical websites on Earth.

It’s darkish, its ambiance is regular, dry and clear, and it is residence to a number of the finest ground-based astronomical infrastructure on the planet.

Atacama is the positioning of the European Southern Observatory’s Very Large Telescope and Very Large Array and, quickly, will probably be residence to a fair greater undertaking: the Extremely Large Telescope.

As a lot of Earth’s darkest skies come underneath menace from mild air pollution, the identify given to the detrimental impact of synthetic mild on our view of the heavens, you would possibly suppose a area as pristinely darkish, as astronomically necessary as Atacama can be secure.

Amazing Atacama astronomy

But not so, it appears.

We spoke to Astrophysicist Itziar de Gregorio-Monsalvo, the European Southern Observatory (ESO)’s consultant in Chile, to search out out extra.

What makes the Atacama Desert a first-rate location for trying on the cosmos? 

Chile is the most effective place on Earth for doing astronomy in numerous wavelengths.

We have very clear and quiet skies, that are good for observations within the optical and infrared.

We even have excessive, dry locations within the mountains that are good for ‘millimeter’ and ‘submillimeter’ astronomy.

Observing websites just like the European Southern Observatory (ESO) Paranal web site are in the midst of the Atacama Desert, removed from massive cities and their related mild air pollution. 

What is mild air pollution?

It’s the brightening of the sky attributable to the surplus mild that we human beings emit into the ambiance.

We emit a considerable amount of pointless mild – say, from poorly positioned streetlamps and the blue mild element of LEDs – which might brighten the sky far-off from the air pollution’s supply.

How does it have an effect on astronomy?

It limits our potential to look deep into the Universe, notably utilizing optical astronomy.

When we observe with a telescope, we are able to’t differentiate mild coming from the cosmos and lightweight coming from mild air pollution.

So we are able to’t see very faint objects, comparable to Earth-like planets near different stars.

What is threatening the standard of skies over ESO websites in Chile?

We’re being uncovered to threats from industrial tasks near our Paranal observatories – enormous tasks, nearly like mini cities, that require giant quantities of sunshine for secure operation.

One such undertaking, INNA, which is a inexperienced hydrogen web site, would sit very close to the proposed south web site of the Cherenkov Telescope Array Observatory (CTAO-South).

Could which have a large affect at Paranal? 

Yes. The blue photons that CTAO-South would observe are extraordinarily delicate to mild air pollution that we count on the INNA undertaking will trigger.

The undertaking may also depend on a wind farm for power, which is prone to shake the bottom and trigger vibrations that can affect the delicate mirror alignment of the upcoming Extremely Large Telescope (ELT) and the interferometer VLTI.

The wind farm and photo voltaic plant may also contribute to elevated atmospheric turbulence, which will probably be troublesome to appropriate for and can injury the standard of our optical pictures.

That’s to say nothing of the development part and the related mud and vibration. 

What steps has ESO taken in response to the proposed undertaking? 

We’ve been calculating the affect of the INNA undertaking and located that in the event that they transfer to a secure distance away, the injury from vibrations and lightweight air pollution can be minimised.

We’ve submitted our proposals to the Chilean authorities as a part of the undertaking’s evaluation course of.

This will take time, however Chile is dedicated to defending the standard of its darkish skies – that’s been the case for greater than six a long time. 

How is ESO tackling the broader challenges of sunshine air pollution?

ESO works with the regional authorities of Chile and collaborates with different worldwide observatories to scale back mild air pollution.

We additionally elevate consciousness in order that authorities and the general public perceive why they need to shield the standard of the skies.

Why ought to we care about mild air pollution?

Dark skies are necessary for humanity as a result of they’re the final home windows into the Universe.

If you reside in a giant metropolis, sooner or later you’ll not see the celebs or the Milky Way. You’ll lose reference to the Universe.

On a sensible degree, the know-how we use in astronomy additionally advantages humanity – take the digital digicam, for instance.

This progress will cease if we lose our energy to look at the Universe.

How can folks get entangled? 

It can begin from very primary steps, like altering the lighting exterior your own home, by means of to extra concerned measures, like speaking to your native authorities about what they’re doing to sort out mild air pollution.

This interview appeared within the September 2025 challenge of BBC Sky at Night Magazine