Free Astronomy Magazine January-February 2026

JANUARY-FEBRUARY 2026 ASTRO PUBLISHING which had been conducting surveys for the VISTA telescope since 2008. With 4MOST being a spectrograph, an instrument that is fundamental- ly different from a camera, VISTA needed to be completely upgraded to receive it. “We had to replace many components of the telescope to fit our instrument in, bringing new large optics to the telescope, new technical cameras to control the telescope and then the instru- ment itself,” says Brynnel. “The up- grade of the VISTA telescope to receive the new components was prepared by ESO in advance of 4MOST’s arrival,” explains Jean- François (Jeff) Pirard, ESO Project Manager for 4MOST “The telescope was returned to service during the first semester of 2025 just in time to receive the new 4MOST instru- ment.” The 4MOST first-light obser- vations, which covered an area of the sky containing the Sculptor Galaxy and the NGC288 star cluster, show off this cutting-edge instru- ment’s ability to observe multiple targets with an astonishingly wide field of view and numerous optical fibres. In the first run, 4MOST col- lected spectra for various stars in our Milky Way and for more than a thousand galaxies near and far, demonstrating its impressive capa- bilities. 4MOST Principal Investiga- tor Roelof de Jong, Milky Way section head at AIP, remarks: “It is incredible to see the first spectra from our new instrument. The data looks fantastic from the start and bodes well for all the different sci- ence projects we want to execute. That we can catch the light that has travelled sometimes for billions of light years into a glass fibre the size of a hair is mindboggling. An in- credible feat only made possible by an incredible development team. Can’t wait till having the system op- erating every night.” T his photograph, taken from the back of the VISTA, show some of the fibers of the 4MOST instrument inside the telescope. [ESO/J. Muñoz] T his photograph, taken at the control room of ESO’s Paranal Observatory, shows part of the 4MOST team closely watching the first data captured by the instrument as the first test observations were performed. [AIP/R. de Jong] scientific output.” This cutting-edge facility will not only shed light on our own home galaxy, but also peer further out at multiple galaxies to piece together how they form and evolve. By observing distant galaxies, 4MOST will also help us better un- derstand dark matter, an invisible form of matter that permeates galaxies and the space between them. The instrument will also be used to study the evolution of the Universe itself, investigating how it expands and changes over time. 4MOST has taken the place of the VISTA Infrared Camera (VIRCAM), can observe at the same time, the large field of view (equivalent to the area of 16 full Moons), and the large number of spectral colours it can register simultaneously make the instrument particularly unique. “This is a major change in the things we do at ESO, usually when you ob- serve with an instrument, you ob- serve targets for one scientific study at a time.” , says Vincenzo Mainieri, ESO Project Scientist for 4MOST. However, due to the large number of fibres, the instrument can ob- serve sources from many different scientific projects simultaneously. He continues: “4MOST can serve 10 or more scientific studies in parallel in one single observation. This is a way to maximise the instrument’s !