82°30′00″ N · 0°00′00″ E

In plain language

What this site actually is

The EXAX project aims to place a single camera on the surface of the Moon and point it permanently at Earth. Not a spacecraft that orbits and looks away every hour, but a fixed eye on solid ground that keeps the whole planet in frame for years on end — a continuous, uninterrupted portrait of Earth as one object in space.

Choosing where to put it is less obvious than it sounds. The Moon always keeps very nearly the same face turned toward Earth, so it is tempting to assume Earth simply hangs motionless in the lunar sky and almost any near-side spot would do. It does not work that way. The Moon does not hold perfectly still as it travels its orbit: it nods and rocks slightly, a slow wobble that swings Earth's apparent position back and forth over a rhythm that takes about 18.6 years to complete. Near the edges of the face we can see, that wobble is enough to drag Earth down to the horizon and, in the wrong spot, briefly behind a hill or crater rim and out of sight. Keeping Earth permanently visible therefore means finding a place where, across the entire 18.6-year cycle and from behind every nearby ridge, the planet never once drops below the local skyline. Settling that took a four-stage investigation: first working out exactly where Earth appears in the sky from each candidate point at every moment, then checking that the real lunar landscape — measured from laser-altimeter maps made from orbit — never rises up to block it.

This particular location lies in the Moon's far north, on the line that points most directly at Earth, in old, worn highland country just south of a crater named Gioja. The ground here is smooth and rounded rather than jagged, and it slopes very gently away in the direction of Earth.

From here Earth never rises and never sets. It hangs low in one corner of the sky and stays there — a large, brilliant ball, roughly three to four times as wide as the full Moon looks from a back garden, and far brighter. Day to day and month to month it drifts slowly within a small patch, tracing a slow loop rather than marching across the heavens; over the years the loop shifts, but Earth always keeps to the same low corner. The camera would catch the planet turning once a day, continents and oceans and weather rolling past, the line between day and night sweeping across its face. And Earth runs through phases, just as the Moon does for us — a slim crescent, a half, a full bright disk — completing the cycle about once a month, always opposite to the Moon's phase in our own sky.

To turn this candidate into a real camera site, the one remaining step is a close-up survey of the ground in the few tens of kilometres toward Earth, mapped finely enough to confirm the exact shape of the horizon down to the last hand's-breadth, so the camera can be set with its view guaranteed clear.