4MOST - 4-metre Multi-Object Spectroscopic Telescope
4-m Multi-Object Spectroscopic Telescope


The 4MOST consortium has been selected by the European Southern Observatory (ESO) to provide the ESO community with a fibre-fed spectroscopic survey facility on the VISTA telescope with a large enough field-of-view to survey a large frac­tion of the southern sky in a few years. The facility will be able to simultaneously obtain spectra of ~2400 objects distributed over an hexagonal field-of-view of 4.2 square degrees. This high multiplex of 4MOST, combined with its high spectral resolution, will enable detection of chemical and kinematic substructure in the stellar halo, bulge and thin and thick discs of the Milky Way, thus help unravel the origin of our home galaxy. The instrument will also have enough wavelength coverage to secure velocities of extra-galactic objects over a large range in red­shift, thus enabling measurements of the evolution of galaxies, black holes, and the structure of the cosmos.

This exceptional instrument enables many science goals, but the design is especially intended to complement three key all­-sky, space­-based ob­servatories of prime European interest: Gaia, Euclid, and eROSITA. Such a facility has been identified as of critical importance in numerous European strategic documents (Bode et al. 2008; de Zeeuw & Molster 2007; Drew et al. 2010; Turon et al. 2008) and forms the perfect com­plement to the many all­-sky survey pro­jects around the world.

4MOST is currently in its Manufacturing, Assembly, Integration and Test Phase with an expected start of full science operations in Q2 2024.



4MOST enables many science goals, but its design in particular complements a number of key large-area, space­-based observatories of prime European interest: Gaia, eROSITA, Euclid, and PLATO, and future ground-based, wide-area survey facilities like the Vera C. Rubin Observatory and SKA. 4MOST will unfold maximum impact by operating continuously for an initial five-year Public Survey programme delivering spectra for ≥25 million objects over ≥15 000 square degrees.

The first five-year survey of 4MOST consists of 10 Programmes developed by the Consortium and 15 Programmes from the ESO community. Read more about 4MOST science and the survey programme.


The 4MOST Facility comprises the instrument as well as the software to schedule and observe many surveys in parallel, and the data management system to reduce, analyse, validate and publish all data, including higher-level data products (radial velocities/redshifts, stellar parameters, abundances, etc.).

Find out more about the facility.


The 4MOST consortium consists of 15 institutes in Germany, Australia, France,  the Netherlands, Sweden, Switzerland, and the UK, under leadership of the Leibniz-Institut für Astrophysik Potsdam (AIP).

See all consortium partners and their roles.