The four faces look cold, and they were. In December 1986 the men of U2 stood at Zabriskie Point in Death Valley, peeled off their coats so the picture would read as desert heat, and let the freezing air do the rest. Bono later admitted that the grim, hollow-eyed seriousness on the cover came partly from the temperature. The body remembers what the eye cannot see.

They are four men in black, tightly grouped in the left of a wide horizontal panel, every gaze pulling somewhere different so the cluster feels watchful rather than posed. One wears a brimmed hat. One stares straight out at you. Behind them a vast, eroded basin of pale hills falls away toward distant mountains, the whole scene rendered in silver greys and deep shadow.

Look at the photograph and you understand the trade they made: comfort for atmosphere, warmth for gravity. The image would go on to send strangers wandering into the sand for decades, chasing something it only ever promised.