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THANKS to my book release, I have been giving a lot of talks about which means I get the opportunity to introduce people to the cosmological timeline and what we know about it.

On an early slide in these talks, I introduce an important before and after: there’s the universe before light starts travelling freely through and then there’s after. This shift happens at about 380,000 years after the big bang (or whatever came before), when, for the first time, the universe is transparent to light. Before this, the universe is full of what I jokingly call a plasma particle stew that is so dense it is opaque to light; light can’t travel far without hitting something.

Today, we can see the light from the moment of transition from opaque to transparent – this is what we call the microwave background radiation (CMB). The word “radiation” can be anxiety-inducing for people, so I usually tell people not to worry as the CMB has been around for about 13 billion years and humans evolved in a universe where it is everywhere. Even though we couldn’t see it and weren’t aware of it until about 60 years ago, the CMB has always been with us.

This dynamic more broadly exemplifies a fact about our species: we are a small piece of the universe that has evolved alongside the unfolding of the great cosmic timeline. Part of our specific experience with this is growing up – as a species and as individuals – under a night sky that was relatively predictable, but also occasionally changed.

For example, some celestial objects were so easy to see with the naked eye and so persistent in their patterns that communities around the world gave names to the shapes they saw in them. These constellations stay with us today. Even those of us who don’t take astrology seriously typically know which constellation we were born under. And many of us look for familiar constellations like the Big Dipper, also known as the Plough, when we go stargazing.

Occasionally there are dramatic changes. In the year AD 1006, a star blew up into a supernova. It remains the brightest stellar event on record, and observations were noted by communities across North America, Africa, the Middle East, Asia and Europe. In other words, humans have long been attuned to the night sky, even before instruments like telescopes were available or in widespread use.

“The night sky may forever look dramatically different to us than it did to our ancestors”

The ability to be so in tune with the dramas of the greater universe was predicated on access to a dark night sky. We as a species came of age through millennia where darkness at night was near total, making the planets and stars easy to spy. Only more recently has our experience of the night changed dramatically. As electricity became widely available and populations became more concentrated in brightly lit urban areas, these dynamics changed.

It is no longer a given that someone will know what the Milky Way looks like. I grew up in the highly polluted Los Angeles of the 1980s and 1990s, where we saw the moon, maybe and often little else.

These limitations are tragic. Not only is air pollution a threat to our bodies, but light pollution is a threat to wildlife by, for example, disrupting the breeding activity of nocturnal animals.

When people miss out on the wonders of the cosmos, they miss out on making a connection that is part of who we are as people.

The majestic telescope images produced by astronomers are also affected by light and air pollution.

Today, the challenges aren’t all coming from the ground, where our cars and fireplaces are emitting pollution and our street lamps are making it difficult to see the sky. We now also have to contend with the satellites that we launch into the sky, which can be disruptive to our ability to see the cosmos beyond what is hanging around in low Earth orbit.

Though it can be fun to play spot the Space Station, with the launch of commercial crewed space flight and poorly regulated, billionaire-owned satellite constellations, the night sky may forever look dramatically different to us than it did to our ancestors. Ostensibly, the humanist argument for launching tens of thousands of satellites into space is that they can provide internet to rural areas. However, an alternative approach would be to tax billionaires to fund on-the-ground infrastructure.

As of now, these constellations are such a radical transformation to the night sky that astronomers are hosting meetings about how to deal with the damage they are projected to do to observational astronomy. It’s easy to argue that these artificial satellite constellations are part of a necessary technological advance. But I have to wonder what it means to forever change the sky, leaving our ancestral heritage more difficult to recognise.