Pondering the dreadful inevitability of our demise, the grand tragedies, political unrest and murderous regimes that daily beset the inhabitants of planet Earth, nothing, to my mind, is more reassuring than the night sky. It makes us feel small in the best way possible: it’s an infinite metaphor for the ultimate insignificance of our collective stupidity/brilliance/beauty. On the 14 September 2016, the European Space Agency (ESA) made an announcement: ‘On its way to assembling the most detailed 3D map ever made of our Milky Way galaxy, Gaia has pinned down the precise position on the sky and the brightness of 1,142 million stars.’ Gaia – named after the goddess who, in Greek mythology, personified the Earth and is the mother of the sky – is a spacecraft with a billion-pixel camera, two telescopes and ten mirrors. It set off on its celestial journey in December 2013; since then, it’s been faithfully cataloguing outer space from its vantage point of around 1,000,000 miles away from Earth. (Oh, imagine the peace of that!) The data it has sent back home is 1,000 times more accurate than any that has come before.
The next map will be released later this year. Alvaro Giménez, ESA’s director of science, declared that this ‘extraordinary data [...] will revolutionize our understanding of how stars are distributed and move across our galaxy’. But the project isn’t just about stars. Gaia’s lead scien- tist, Timo Prusti, has said that the final survey ‘will contain 250,000 new solar system objects, 1,000,000 distant galaxies, 500,000 quasars – and about 20,000 exoplanets’. Hopefully, Gaia will also be able to identify asteroids that may one day threaten our planet.
One billion stars is only about one percent of the Milky Way’s stellar population. Quite apart from its staggering scientific use, the map is a beautiful iteration of something we humans need to remind ourselves of more often: that there is still an awful lot that we know nothing about.
First published in Issue 184