New MOONS: the cold cameras that will probe hidden stars

Two infrared cameras inside MOONS will help astronomers investigate stars concealed behind the Milky Way’s dust. Suspended in darkness in this ESO image, their tiered metal structures, bolts and cables reveal the engineering behind a new instrument at the Very Large Telescope that has recently made its first observations.

MOONS stands for Multi Object Optical and Near-infrared Spectrograph. Infrared light (radiation at wavelengths longer than visible light) can penetrate dust that obscures the Galaxy’s inner stars, allowing astronomers to examine populations otherwise hidden from view.

Around 1000 fibre-optic cables, each guided by a robotic positioner, collect light from individual astronomical targets and feed it into two spectrographs. These instruments separate light into its constituent wavelengths, exposing chemical fingerprints that help researchers determine composition and velocity, and infer properties such as mass.

Cold detectors, a crowded sky

The cameras must distinguish faint astronomical infrared light from radiation emitted by their surroundings. A cryostat (a cooled enclosure) keeps MOONS between –143 and –233 degrees Celsius, reducing contamination from the instrument itself.

Its scientific reach extends from a three-dimensional map of the Milky Way’s centre to studies of millions of galaxies at different ages of the Universe. The connection is spectroscopy: decoding light to reconstruct how stars and galaxies formed and changed.

MOONS observes from the ground, rather than joining the spacecraft population overhead. Orbital Radar tracking data lists 16,687 active satellites in orbit as of 9 November 2026. Orbital Radar’s live catalogue contains 32,084 objects, including debris, as of 9 November 2026.

Those orbital figures describe a different observing challenge from the dust MOONS looks through: distinguishing objects moving around Earth from the distant sky. Readers exploring that distinction can use Orbital Radar’s Pass Predictor to find satellite passes, while MOONS examines the physical information carried by starlight.