The 4-metre Multi-Object Spectroscopic Telescope (4MOST) is a wide-field, high-multiplex, fibre-fed, optical spectrograph mounted on the VISTA telescope.

4MOST features a 2.5-degree diameter field-of-view with 2436 science fibres in the focal plane configured by a tilting spine fibre positioner. The instrument has three fixed-configuration spectrographs:

• A high-resolution spectrograph (HRS) fed by ~812 fibers reaching a resolving power R ~ 18000 - 21000
• Two low-resolution spectrographs (LRS) feb by the remaining ~1624 fibers reaching a resolving power R ~ 4000 - 7500.

Each spectrograph is in turn divided in three wavelenght channels (blue, green and red) before the light is dispersed by VPH gratings. The spectra are then recorded by 6k x 6k E2V CCDs.

The instrument also contains wide field corrector with an atmospheric dispersion corrector, an acquisition, guiding and wavefront sensor system, and metrology and calibration systems.

Detailed description of the instrument is available at 4most.eu

The instrument was designed as a facility for executing large surveys and deliver data for one of the ESO Public Survey Projects for a period of 5 years. The survey is divided in 15 Community Surveys (30% of the observing time) and 10 Consortium Surveys (70% of the observing time).

The 4MOST Survey Management plan provides further details about the Public Data Release plan,