On St Valentine’s Day 1990, NASA’s engineers directed the space-probe Voyager 1 – at the time, 6 billion kilometres (3.7 billion miles) from home – to take a photograph of Earth. Pale Blue Dot (as the image is known) represents our planet as a barely perceptible dot serendipitously highlighted by a ray of sunlight transecting the inky-black of space – a ‘mote of dust suspended in a sunbeam’, as Carl Sagan famously put it. But to find that mote of dust, you need to know where to look. Spotting its location is so difficult that many reproductions of the image provide viewers with a helpful arrow or hint (eg, ‘Earth is the blueish-white speck almost halfway up the rightmost band of light’). Even with the arrow and the hints, I had trouble locating Earth when I first saw Pale Blue Dot – it was obscured by the smallest of smudges on my laptop screen.

The striking thing, of course, is that Pale Blue Dot is, astronomically speaking, a close-up. Were a comparable image to be taken from any one of the other planetary systems in the Milky Way, itself one of between 200 billion and 2 trillion galaxies in the cosmos, then we wouldn’t have appeared even as a mote of dust – we wouldn’t have been captured by the image at all.

Pale Blue Dot inspires a range of feelings – wonderment, vulnerability, anxiety. But perhaps the dominant response it elicits is that of cosmic insignificance. The image seems to capture in concrete form the fact that we don’t really matter. Look at Pale Blue Dot for 30 seconds and consider the crowning achievements of humanity – the Taj Mahal, the navigational exploits of the early Polynesians, the paintings of Georgia O’Keeffe, the inventions of Leonardo da Vinci, John Coltrane’s A Love Supreme, Cantor’s theorem, the discovery of DNA, and on and on and on. Nothing we do – nothing we could ever do – seems to matter. Pale Blue Dot is to human endeavour what the Death Star’s laser was to Alderaan. What we seem to learn when we look in the cosmic mirror is that we are, ultimately, of no more significance than a mote of dust.

Contrast the feelings elicited by Pale Blue Dot with those elicited by Earthrise, the first image of Earth taken from space. Shot by the astronaut William Anders during the Apollo 8 mission in 1968, Earthrise depicts the planet as a swirl of blue, white and brown, a fertile haven in contrast to the barren moonscape that dominates the foreground of the image. Inspiring awe, reverence and concern for the planet’s health, the photographer Galen Rowell described it as perhaps the ‘most influential environmental photograph ever taken’. Pale Blue Dot is a much more ambivalent image. It speaks not to Earth’s fecundity and life-supporting powers, but to its – and, by extension, our – insignificance in the vastness of space.

Earthrise, taken on 24 December 1968 by Apollo 8 astronaut William Anders. Courtesy NASA

But what, exactly, should we make of Pale Blue Dot? Does it really teach us something profound about ourselves and our place in the cosmic order? Or are the feelings of insignificance that it engenders a kind of cognitive illusion – no more trustworthy than the brief shiver of fear you might feel on spotting a plastic snake? To answer that question, we need to ask why Pale Blue Dot generates feelings of cosmic insignificance.

One account of the feelings elicited by Pale Blue Dot begins in the 17th century, with the French scientist and philosopher Blaise Pascal. Pascal was born in 1623, a mere 14 years after Galileo directed the first telescope heavenwards. Galileo’s observations not only confirmed Copernicus’s heliocentric conception of the solar system and revealed ‘imperfections’ in the celestial bodies (such as the Moon’s craters and mountains), they also revealed countless stars invisible to the naked eye. It was a moment of profound upheaval for humanity’s self-understanding, and many of the reflections recorded in Pascal’s Pensées – a series of notebook jottings published only after Pascal’s death – seem to have been prompted by the new astronomy:

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