Fifty years ago, the location of our sun relative to the centre of the Milky Way was etched onto four metal plaques which were launched into deep space attached to the NASA Pioneer and Voyager space probes. The hope was that if any space-faring intelligences came across one of the craft, they would be able to use the plaque to calculate where it originated from.

Encoded in a diagram on the plaques, in binary, are the unique pulse periods of 14 fast-spinning, super-dense neutron stars (pulsars) whose emanations are detectable from Earth. Pulsars are so regular, and so far distant, that they form some of the most stationary, permanent and reliable ‘landmarks’ in the universe. If a few are also visible to other intelligences, there is a (very small) chance they could be used – by triangulation, similarly to how satellites provide GPS coordinates – to compute the location of the Sun.

The furthest plaque is now 23 billion kilometres from the Sun (around 160 times the distance from the Sun to the Earth), or nearly one light day. Some of the 14 pulsars are over 25,000 light years away.

In 1967 the first pulsar was discovered by Dame Jocelyn Bell. Now known as CP 1919, its unique radio frequency signature forms the dataset used to create the cover art for Joy Division’s 1979 album Unknown Pleasures.

Pulsars can’t be seen, heard or felt. They move through the heavens as stars move. Their apparent locations can be calculated from their positions relative to the standard equinox (a galactic location) and the current local sidereal time (the ‘hour angle’ of the equinox to North).

Unknown Pressures depicts the pulsars where they would have been, relative to Broken Hill’s Line of Lode, at the moment of the southern spring equinox in 2022.