Night Sky

Protecting natural darkness

Project summary

Dark nights are important for human health, plant development and ecosystem stability, but growing numbers of satellites could brighten our night skies. The extent of the consequences, and whether they can be reversed, remains uncertain.

Help protect our nights by writing to your MP, sharing reliable information and responding to public consultations. We would like governments to fund research and put in place regulations that will manage satellite brightness both nationally and internationally.

Project content compiled by Lorena Rosen.

Why does darkness matter?

What could make the night sky brighter?

What do we still need to understand?

Why is this an international concern?

International appeal to the US regulator

What we are asking the UK government to do

What you can do

Resources and more information

Why does darkness matter?

All living things have internal body clocks that follow the natural cycle of day and night. These body clocks affect health, behaviour and survival. Artificial light at night can throw them off.

Research shows that artificial light at night can affect:

Plants and food production: altering growth, flowering and seed production, and disrupting relationships with pollinators.
Marine ecosystems: changing behaviour and reproduction in organisms including plankton, corals and fish. Potential effects on marine carbon cycling need investigation.
Wildlife: disrupting navigation, migration, feeding, predator avoidance and reproductive timing.
Human health: shifting circadian rhythms, suppressing melatonin and disrupting sleep. Mistimed light exposure is associated with poorer health outcomes.

Most of this evidence is based on terrestrial lighting. The additional exposure from satellite skyglow and its biological significance must be researched further.

What could make the night sky brighter?

Satellites reflect sunlight. Their size, design, altitude and orientation determine how bright they appear and how much they add to background sky brightness or ‘skyglow’.

Two projects we are concerned about are:

SpaceX's proposed orbital data centres: an application to the US Federal Communications Commission (FCC) for up to one million satellites to support space-based computing.
Reflect Orbital's proposed 'sunlight as a service': orbiting mirrors that would direct sunlight towards Earth at night, with an ambition of 50,000 satellites by 2035. The FCC authorised a demonstration satellite in July 2026.

Satellites already interfere with astronomical observations, and a 2026 European Southern Observatory study found that proposed constellations could substantially increase background sky brightness further. The implications, however, extend well beyond astronomy.

What do we still need to understand?

The central questions are how much additional light these projects would introduce, where and when exposure would occur, and what the consequences would be.

We need to better understand:

the cumulative brightness of multiple constellations
which light intensities, wavelengths and exposure patterns could be detected by the clocks in organisms and cause biological disruption
which species and ecosystems are most vulnerable
the potential long-term effects on biodiversity, food production and marine carbon cycling
whether/how the illumination, and any resulting ecological changes, could be reversed

Why is this an international concern?

Satellite skyglow crosses borders. Satellites authorised by one country can affect environments in many others, beyond the reach of local lighting controls.

Satellites also provide valuable communications, navigation and Earth-observation services. Preserving these benefits while preventing avoidable harm requires international cooperation and an assessment of cumulative impacts rather than just of individual projects.

International appeal to the US regulator

On 5 March 2026, the presidents of four international biological-rhythm societies, representing scientists in more than 30 countries, wrote to the FCC about the Reflect Orbital and SpaceX proposals and their potential risks.

The appeal called for:

a comprehensive Environmental Impact Statement before any large-scale authorisation
assessment of biological, ecological and biogeochemical effects
independent, interdisciplinary expertise
measurable reflectivity standards and cumulative brightness thresholds

You can view the full letter here.

What we are asking the UK Government to do

Our response to the UK Space Resilience Inquiry argued that protecting natural darkness should be part of environmental protection and national resilience.

As chronobiologists, we offer biological expertise and propose the need for an interdisciplinary approach to policy changes. Policy should draw on scientific, ecological, engineering and economic evidence. Recommendations are already being published by other groups such as the Space Economy Initiative 'Crowded orbits, fading skies: a policy framework for satellite mega-constellations'

We recommended seven actions:

Convene an interdisciplinary advisory group to develop a national skyglow strategy.
Fund research into biological effects, exposure thresholds, vulnerable ecosystems and ways to reduce satellite brightness.
Include cumulative satellite illumination in relevant environmental assessment and licensing processes, for example through the Civil Aviation Authority.
Commission an independent review of risks to UK biodiversity, particularly pollinators, migratory species and marine ecosystems.
Raise the issue of satellite skyglow at the UN Committee on the Peaceful Uses of Outer Space (COPUOS), proposing an international working group.
Develop international brightness standards and shared practices for minimising orbital light pollution.
Include satellite skyglow in national resilience and risk assessments.

You can view the BioClocks UK response to the government inquiry here.

What you can do

Protecting the night-time environment requires action across government, industry, research and society.

Write to your MP. Raise awareness and ask your MP to take action – you can use our template to get you started.
Share reliable information. Use the resources shared here to raise awareness with your network.
Contribute to consultations. Where appropriate, respond to relevant regulatory consultations and parliamentary inquiries. You can keep updated by signing up to the parliament’s Knowledge Exchange Unit regular roundup.
Raise the issue internationally. If you live outside the UK, contact representatives in your own country.