But since these high energy particles have an estimated arrival rate of just 1 per km2 per century, the Auger Observatory has created a detection area of 3,000 km2 (1,200 sq mi)—the size of Rhode Island, or Luxembourg—in order to record a large number of these events.

The northern site was to be located in southeastern Colorado, United States and hosted by Lamar Community College.

Today, more than 500 physicists from nearly 100 institutions around the world[2] are collaborating to maintain and upgrade the site in Argentina and collect and analyse the measured data.

Passing through the atmosphere, this plane of particles creates UV light, invisible to the human eye, called the fluorescing effect, more or less in the pattern of straight lightning traces.

These traces can be photographed at high speed by specialised telescopes, called Fluorescence Detectors, overlooking an area at a slight elevation.

Then, when the particles reach the Earth's surface, they can be detected when they arrive in a water tank, where they cause visible blue light due to the Cherenkov effect.

When an air shower hits multiple Cherenkov Detectors on the ground, the direction of the ray can be calculated using basic geometrics.

The fluorescence detectors are used to track the particle air shower's glow on cloudless moonless nights, as it descends through the atmosphere.

It was used to make more detailed design choices (like which type of photomultiplier tube (PMT) to use, and tank water quality requirements) and to calibrate.

The basic set-up consists of 1600 water Cherenkov Detectors or 'tanks', (similar to the Haverah Park experiment) distributed over 3,000 square kilometres (1,200 sq mi), along with 24 atmospheric Fluorescence Detector telescopes (FD; similar to the High Resolution Fly's Eye) overseeing the surface array.

[6] A subsequent test with a much larger data sample revealed however that the large degree of initially observed correlation was most probably due to a statistical fluctuation.

[7] In 2017, data from 12 years of observations enabled the discovery of a significant anisotropy of the arrival direction of cosmic rays at energies above 8×1018 eV.

The Pierre Auger Collaboration has made available (for outreach purposes) 1 percent of the ground array events below 50 EeV (1018 eV).

As of October 2021, a portion of the data (10 percent) presented at the 2019 International Cosmic Ray Conference in Madison, USA, is publicly available.