Since time immemorial, humans around the world have gazed up in wonder at the night sky. The starry night sky has not only inspired countless works of music, art, and poetry but has also played an important role in timekeeping, navigation and agricultural practices in many traditions.

For many cultures, the night sky, with its stars, planets and the Milky Way, is considered just as important a part of the natural environment as the forests, lakes and mountains below. Countless people around the world gaze at the night sky: not only amateur and professional astronomers, but also casual observers who enjoy looking up at the stars to contemplate our place in the cosmos.

However, the night sky is changing. Not only is ground-based light pollution increasing rapidly, but growing numbers of satellites and space debris in orbit around Earth are also impacting the night sky.

Earlier research showed that satellites and space debris may increase the overall brightness of the night sky. In a new paper in Nature Astronomy, my colleagues and I applied this knowledge to predicting the performance of a major astronomical sky survey. We found this phenomenon may make the survey 7.5 percent less efficient and US$21.8 million (roughly Rs. 180 crore) more expensive.

A brighter sky

As a cultural astronomer, I am interested in the role of the night sky in cultural traditions around the world. In particular, I am interested in how light pollution and increasing satellite numbers affect different communities.

The number of satellites in orbit is growing rapidly. Since 2019, the number of functional satellites in orbit has more than doubled to around 7,600. The increase is mostly due to SpaceX and other companies launching large groups of satellites to provide high-speed internet communications around the world.

By the end of this decade, we estimate, there may be 100,000 satellites in orbit around the Earth. Collisions that generate space debris are more likely as space fills with new satellites. Other sources of debris include the intentional destruction of satellites in space warfare tests.

Increasing numbers of satellites and space debris reflect ever more sunlight towards the night side of Earth. This will almost certainly change the appearance of the night sky and make it harder for astronomers to do research.

One way satellites impact astronomy is by appearing as moving points of light, which show up as streaks across astronomers’ images. Another is by increasing diffuse night sky brightness. This means all the satellites that are too dim or small to be seen individually, as well as all the small bits of space debris, still reflect sunlight, and their collective effect is to make the night sky appear less dark.

Hard times for astronomers

In our research, we present the first published calculations of the aggregate effects of satellites and space debris in low-Earth orbit on major ground-based astronomy research facilities.

We looked at the effect on the planned large-scale survey of the night sky to be carried out at the Vera Rubin Observatory starting in 2024. We found that, by 2030, reflected light from objects in low-Earth orbit will likely increase the diffuse background brightness for this survey by at least 7.5 percent compared to an unpolluted sky.

This would diminish the efficiency of this survey by 7.5 percent as well. Over the ten-year lifetime of the survey, we estimate this would add some $21.8 million (roughly Rs. 180 crore) to the total project cost.

Brighter night skies mean longer exposures through telescopes are needed to see distant objects in the cosmos. This will mean that for projects with a fixed amount of observing time, less science will be accomplished, and there will be increased competition for telescope access.

In addition, brighter night skies will also reduce the detection limits of sky surveys, and dimmer objects may not be detected, resulting in missed research opportunities.

Some astrophysical events are rare and if researchers are unable to view them when they occur, there might not be an opportunity to easily see a given event again during a survey’s operational period. One example of faint objects is near-Earth objects – comets and asteroids in orbits close to Earth. Brighter night skies make it more likely such potentially hazardous objects may remain undetected.

A dramatic and unprecedented transformation

Increases in diffuse night sky brightness will also change how we see the night sky with the unaided eye. As the human eye cannot resolve individual small objects as well as a telescope can, an increase in satellites and space debris will create an even greater increase in the apparent brightness of the night sky. (When using a telescope or binoculars, one would be able to make out more of the dimmer satellites individually.) The projected increase in night sky brightness will make it increasingly difficult to see fainter stars and the Milky Way, both of which are important in various cultural traditions. Unlike “ground-based” light pollution (which tends to be the worst near large cities and heavily populated areas), the changes to the sky will be visible from essentially everywhere on Earth’s surface.

Our models give us a conservative lower limit for a likely increase in night sky brightness. If numbers of satellites and space debris continue to grow at the expected rate, the impacts will be even more pronounced.

As we note in our paper, “we are witnessing a dramatic, fundamental, and perhaps semi-permanent transformation of the night sky without historical precedent and with limited oversight”. Such a transformation will have profound consequences for professional astronomy as well as for anyone who wishes to view an unpolluted night sky.

In 2019, the Event Horizon Telescope (EHT) collaboration produced the first-ever image of a black hole, stunning the world.

Now, scientists are taking it further. The next generation Event Horizon Telescope (ngEHT) collaboration aims to create high-quality videos of black holes.

But this next-generation collaboration is groundbreaking in other ways, too. It’s the first large physics collaboration bringing together perspectives from natural sciences, social sciences and the humanities.

For a virtual telescope spanning the planet, the larger a telescope, the better it is at seeing things that look tiny from far away. To produce black hole images, we need a telescope almost the size of Earth itself. That’s why the EHT uses many telescopes and telescope arrays scattered across the globe to form a single, virtual Earth-sized telescope. This is known as very long baseline interferometry.

Harvard astrophysicist Shep Doeleman, the founding director of the EHT, has likened this kind of astronomy to using a broken mirror. Imagine shattering a mirror and scattering the pieces across the world. Then you record the light caught by each of these pieces while keeping track of the timing, and collect those data in a supercomputer to virtually reconstruct an Earth-sized detector.

The 2019 first-ever image of a black hole was made by borrowing existing telescopes at six sites. Now, new telescopes at new sites are being built to better fill in the gaps of the broken mirror. The collaboration is currently in the process of selecting optimal places across the world, to increase the number of sites to approximately 20.

This ambitious endeavour needs over 300 experts organised into three technical working groups and eight science working groups. The history, philosophy and culture working group has just published a landmark report outlining how humanities and social science scholars can work with astrophysicists and engineers from the first stages of a project.

The report has four focus areas: collaborative knowledge formation, philosophical foundations, algorithms and visualisation, and responsible telescope siting.

How can we all collaborate? If you’ve ever tried to write a paper (or anything!) with someone else, you know how difficult it can be. Now imagine trying to write a scientific paper with over 300 people.

Should one expect each author to believe and be willing to defend every part of the paper and its conclusions? How should we all determine what will be included? If everyone has to agree with what is included, will this result in only publishing conservative, watered-down results? And how do you allow for individual creativity and boundary-pushing science (especially when you are attempting to be the first to capture something)? To resolve such questions, it’s important to balance collaborative approaches and structure everyone’s involvement in a way that promotes consensus, but also allows people to express dissent. Diversity of beliefs and practices among collaboration members can be beneficial to science.

How do we visualise the data? The aesthetic choices regarding the final black hole images and videos take place in a broader context of visual culture.

In reality, blue flames are hotter than flames appearing orange or yellow. But in the above false-colour image of Sagittarius A* – the black hole at the centre of the Milky Way – the colour palette of orange-red hues was chosen as it was believed orange would communicate to wider audiences just how hot the glowing material around the black hole is.

This approach connects to historical practices of technology-assisted scientific images, such as those by Galileo, Robert Hooke, and Johannes Hevelius. These scientists combined their early telescopic and microscopic images with artistic techniques so they would be legible to non-specialist audiences (particularly those who did not have access to the relevant instruments).

How philosophy can help Videos of black holes would be of significant interest to theoretical physicists. However, there is a bridge between formal mathematical theory and the messy world of experiment where idealised assumptions often do not hold up.

Philosophers can help to bridge this gap with considerations of epistemic risk – such as the risk of missing the truth, or making an error. Philosophy also helps to investigate the underlying assumptions physicists might have about a phenomenon.

For example, one approach to describing black holes is called the “no-hair theorem”. It’s the idea that an isolated black hole can be simplified down to just a few properties, and there’s nothing complex (hairy) about it. But the no-hair theorem applies to stable black holes. It relies on an assumption that black holes eventually settle down to a stationary state.

Responsible telescope siting The choice of locations for telescopes, or telescope siting, has historically been determined by technical and economic considerations – including weather, atmospheric clarity, accessibility and costs. There has been a historic lack of consideration for local communities, including First Nations peoples.

As the struggle at Mauna Kea in Hawai’i highlights, scientific collaborations are obligated to address ethical, social and environmental considerations when siting.

The ngEHT aims to advance responsible siting practices. It draws together experts in philosophy, history, sociology, community advocacy, science, and engineering to contribute to the decision-making process in ways that include cultural, social and environmental factors when choosing a new telescope location.

Overall, this collaboration is an exciting example of how ambitious plans demand innovative approaches – and how sciences are evolving in the 21st century.

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