News
Countdown to 4MOST First Light
2025-10-14
VISTA and 4MOST at the end of a long and twisty journey. (Credit: Florence Laurent)
First Light Release:
The road to discovery is rarely straight, but every twist and turn has brought us closer. We are nearly there, 4MOST is approaching First Light! All the years of planning, engineering, testing and teamwork are bringing us close to the moment that will enable transformative science across the southern sky. A huge thanks to everyone whose dedication has brought us to this milestone!
Stay tuned for First Light!
4MOST Milestone: AIV Completion - Beginning of Systems Verification
2025-09-25
The Cassegrain Cable Wrap being installed at the VISTA telescope. (Credit Allar Saviauk, AIP)
The Wide Field Corrector carefully being integrated into the telescope. (Credit Allar Saviauk, AIP)
On 17th September 2025, installation of 4MOST onto the VISTA telescope was completed. This marks the end of the Assembly, Integration, Verification (AIV) phase of 4MOST's journey towards observing the Universe. As Joar Brynnel remarks, "this has been a long process, with phased implementation of hardware and software on Paranal".
AIV initially began on 2nd June 2024 with installation of the Cassegrain Cable Wrap. Installation of the Wide-Field Corrector, the Guiding and Wavefront Sensor system, and the control hardware and software followed in October and November 2024, marking an end to phase 1 of AIV. AIV phase 2 began in June 2025, which saw installation of more control hardware and software, Metrology system, Calibration system, Long Fibre Feed, Fibre-Positioner (AESOP), Low-Resolution Spectrographs, and lastly the High-Resolution Spectrograph.
A spectrograph being lifted through the VISTA dome opening. (Credit Allar Saviauk, AIP)
Allar Saviauk and the AIP have done a fantastic job of documenting the AIV process, taking many pictures and producing multiple short films that give amazing insights into the work that has gone on behind the scenes:
The end of AIV means that 4MOST now enters the System Verification phase. Mark Cunningham (System Verification lead) summarised System Verification as the phase "where all the AIV work gets put to the test", with tests designed and carried out to ensure that all of the subsystems "work together as one coherent system". Some of the tests that will be conducted include fibre-to-target alignment, fibre positioning precision, checking for any stray light, and verifying the behaviour of the atmospheric dispersion corrector.
The completion of AIV serves as a reminder of the collective efforts that make projects like 4MOST possible. We wish the System Verification team good luck as they advance 4MOST closer to operations!
The hardware components of 4MOST are fully installed on the VISTA telescope. The telescope is ready to capture its first starlight! (Credit Allar Saviauk, AIP)
4MOST Social Media Launch
2025-09-18
The VISTA telescope, where 4MOST will explore the cosmos with unprecedented detail. (Credit: Y. Beletsky, ESO).
The Science Communication working group are excited to announce that 4MOST is now active on multiple social media platforms. You can now follow 4MOST on LinkedIn, Bluesky, and Instagram to stay up to date with news, project updates, behind the scenes insights, science highlights, and learn about the team behind it all.
Find us here:
We are excited to share with you the work being done across the 4MOST community!
4MOST installation on VISTA
2025-09-12
The installed cassegrain cable wrap (white and orange parts) with the fibre positioner and its near 2500 fibres encased within (Credit: Allar Saviauk).
In June 2025 the last subsystems of 4MOST were shipped from the AIP, Germany, to Paranal, Chile. We are glad to report that all of the shipments arrived safely at the VISTA telescope and that 4MOST in its entirety is now at Paranal.
With the arrival of the final shipments at Paranal, installation of the various subsystems has been carried out by the many specialist teams. The metrology system that monitors the fibre spine positions was installed and calibrated using the focal surface test tool. The test tool was then removed from the focal plane and the team from AAO reintegrated, tested, and installed the fibre positioner onto the telescope. A team from MPIA then installed 4MOST's electronic cabinets and wiring for all of the systems. Finally, the cassegrain cable wrap and the almost 2500 fibres were installed, with the fibres being connected to the fibre positioner.
The two low resolution spectrographs installed side by side under the main telescope platform.
The recent shipments also included the two low resolution and the high resolution spectrographs. As these were dismantled for shipping, they have been reassembled and aligned in the New Integration Hall at Paranal Base Camp by teams from CRAL and AIP. The two low resolution spectrographs have been reassembled and tested, meeting all of their specification requirements and even exceeding many. On the 5th and 7th of September the low resolution spectrographs were craned into the VISTA dome and installed side by side under the main telescope platform. The high resolution spectrograph currently remains in the New Integration Hall for final checks before being installed on VISTA in the coming weeks.
To demonstrate the hard work that has been taking place at Paranal, Allar Saviauk has produced a short film documenting the recent installation work. The film can be viewed at https://cloud.aip.de/index.php/s/3GF8B3jQiKbTbec.
With the installation of 4MOST nearing completion, we now look forward towards celebrating everyone's hard work with 4MOST's first light!
VISTA with all of 4MOST's subsystems installed with the exception of the high resolution spectrograph (Credit: Allar Saviauk).
ESO Picture of the Week: Fantastic 4MOST
2025-07-23
On the 22nd July 2025, 4MOST featured in ESO's picture of the week. With work well underway to install 4MOST on VISTA, we were treated with an image of the installed fibre positioner, with the backlit fibres positioned to create the Fantastic 4 logo.
In addition to the image, ESO and 4MOST released a video showing the fibre positioner in action as it created the iconic logo. It reveals the precise and coordinated motion of the 2436 fibres as they moved gracefully into place.
ESO's picture of the week article, image, and video can be found at:
- Article and image: https://www.eso.org/public/images/potw2529a/
- Video: https://www.eso.org/public/videos/potw2529a/
This marks an exciting milestone in 4MOST's journey, highlighting the tremendous work and dedication from everyone involved over the years. A huge congratulations!
ESO picture of the week 22/07/2025: The 4MOST fibre positioner installed on VISTA with the backlit fibres positioned to create the Fantastic 4 logo. (Credit: ESO/4MOST/Steffen Frey)
4MOST Milestone: Second Major Shipment to Chile
2025-06-18
Last look at the fibre positioner before packing. (Credit Roelof de Jong)
On the 9th May 2025, ESO gave the green light to start packing some of the subsystems at the AIP, Germany, for shipment to Paranal, Chile.
Work began on detatching the fibre system from the fibre positioner and removing the fibre slits from the spectrographs. The smaller subsystems (detectors, fibre feed, electronics cabinets, calibration system, metrology, and secondary guiding) were then shipped by airfreight on the 20th May and safely arrived in Santiago, Chile, on the 29th May.
On the 13th June, ESO and the 4MOST consortium held a meeting regarding preliminary acceptance in Europe (PAE). 4MOST successfully passed PAE, initiating the final shipment which predominantly contains the spectrographs.
With the AIP integration hall now looking rather empty, we are one step closer to the start of operations. In the coming months, we look towards installing and commissioning 4MOST on VISTA.
Spectrographs packed and ready for shipping. (Credit Roelof de Jong)
SITCOM Observing School
2025-04-22
The 1.22m Galileo telescope used by the members of SITCOM during the observing school. (Credit Romain Lucchesi)
During the week beginning 7th April, nine members of SITCOM were hosted at the Astrophysical Observatory of Asiago for an observing school. For some members the school provided them with their first observing experience, while it gave other members a chance to refresh their observing knowledge.
During the school the team learnt the basics of observing, including how to determine if and when a target is most optimal to observe, the calibration data that is required for the data reductions, how to setup and observe using the 1.22m Galileo telescope at the Astrophysical Observatory of Asiago, and finally how to reduce the observations.
How many astronomers does it take to observe a galaxy? (Credit Marica Valentini)
Using what they had learnt, they planned and executed three nights of observations using the 1.22m Galileo telescope. The team observed a number of targets including galaxies such as NGC4565 and M104, planetary nebular, binary stars, and transient events. In particular, the group observed three objects of high interest: Nova X SER, T Corona Borealis, and an unclassified supernova-like transient. The unclassified transient was initially classified as a supernova II and continues to be monitored by staff at the Astrophysical Observatory of Asiago.
The attending SITCOM members thank Marica Valentini for organising the school, and to the staff at the Astrophysical Observatory of Asiago for hosting.
Science Team Meeting 2025
2025-03-13
The most recent 4MOST Science Team Meeting took place on February 24th-28th 2025 at the University Federico II, Italy, and online.
As 4MOST nears the start of operations, this meeting focused on the ongoing and future preparations required for a successful survey start. There were many in-depth discussions surrounding the survey strategy and simulations, with surveys communicating and converging on the future progression of the strategy and simulations. Plans for the phases leading up to the start of operations were discussed, with sessions focusing on the plans for commissioning and operation rehearsals.
Although the meeting primarily focused on the technical preparations, there were also sessions focused on science. There were discussions regarding the plans for DR0, the publication process, and the communication of 4MOST science to public audiences. Additionally, the wide range of science talks displayed the ongoing and future science projects that 4MOST will facilitate. All available presentations and recordings can be found on Docushare.
Overall, this science team meeting was a success, although it highlighted that there is still plenty of work to be done before the start of operations.
On site participants at the University Federico II.
4MOST Wide Field Corrector checks out
2025-03-06
WFC in Paranal clean room during throughput measurement (Credit: Joar Brynnel / 4MOST Consortium)
During the 4MOST hardware integration campaign on Paranal in October 2024, one of the verification measurements done on Paranal during the incoming inspection was the measurement of the Wide Field Corrector optical throughput. At the time, the result of this measurement indicated a loss of optical throughput compared to reference measurements done in Potsdam before shipment. Nevertheless, the WFC was installed on the VISTA telescope and telescope re-commissioning has been ongoing since then.
Possible reasons for the measured loss of throughput have been intensively investigated over the past months, however, since we had no physical access to the WFC, it was not possible to make tests to better understand the root cause of the problem. After discussions between the Consortium and ESO, it was decided to remove the WFC from the VISTA telescope and move it to a clean room on Paranal to investigate the issue. Removing the WFC from the telescope is a complex procedure involving removal of the Cable Wrap system (CaCW), the 4MOST test camera (FSTT), the Guiding and WFS unit, and finally the WFC itself. On 2 March 2025, a team from AIP arrived on Paranal to carry out this work in collaboration with ESO staff.
On 4 March 2025, the WFC optical throughput was re-measured. We are very pleased to report that the results confirm the Potsdam measurements, and the WFC performance is now verified to be nominal and in specifications. Over the next couple of days, we will reinstall all the components on the telescope and the final steps of VISTA re-commissioning can be carried out as planned.
We used the opportunity in the clean room to clean the L1 front and L4 back surfaces with CO2 snow to remove fine dust, as shown in the photo below.
CO2 cleaning of WFC lens surfaces (Credit: Joar Brynel / 4MOST Consortium)
First Technical Light with new Wide Field Corrector and Aquisition & Guiding systems
2024-12-05
4MOST First Technical light image: NGC2207 and IC2163, a pair of overlapping and probably interacting spiral galaxies at about 17 Mpc (55 million light year) distance, surrounded by much nearer stars in our own Galaxy. (Credit: 4MOST Consortium and ESO)
Following the successful 4MOST Paranal installation campaigns in October and November, on November 22 the Consortium and ESO met for the VISTA telescope re-commissioning readiness milestone. The purpose of this milestone was to verify that the VISTA telescope is ready for re-commissioning with the new 4MOST hardware. Once the new Wide Field Corrector and the Acquisition & Guiding and Wave Front Sensing systems have been fully characterized and commissioned, the VISTA telescope will be ready for installation of the remaining 4MOST subsystems, which in turn means start of formal 4MOST verification and commissioning.
We are pleased to report that the November 22 readiness review was successful, which allowed for the start of telescope recommissioning on November 24. It is very exciting to see the VISTA telescope back on sky after being dormant for quite a while. The testing of the telescope has now reached a point where we were able to make images on the technical cameras. With this message, we are delighted to share the official 4MOST “First Technical Light” image with you. The image, taken during the night of December 5, shows the galaxy NG2207. Image quality is already very good, which gives us great confidence in the performance of the VISTA telescope in the new 4MOST configuration.
The amount of work done, enabling the project to reach this milestone, is nothing short of amazing. On behalf of our entire team, we extend our deepest gratitude to each member of the consortium and the ESO support team for your support and dedication. Reaching this significant milestone would not have been possible without your collective efforts, expertise, and commitment.
Looking forward to the next exciting steps towards completing 4MOST!
Joar and Roelof
First Technical Light event in the ESO G-RAF remote control facility in Garching (Credit: Joar Brynnel) From left to right: Dr. Michele Cirasuolo (ESO Instrumentation Programme Manager) Prof. Xavier Barcons (ESO Director General) Dr. Luca Pasquini (ESO Paranal Instrumentation Programme manager) Dr. Adrian Russell (ESO Director of Programmes) Dr. Vincenzo Mainieri (ESO/4MOST Project Scientist) Prof. Matthias Steinmetz (AIP Director) Dr. Norbert Hubin (ESO Instrumentation Programme Engineer) Dr. Johann Kolb (ESO Adaptive Optics Physicist) Dr. Diogo Rio Fernandes (ESO/4MOST Systems Engineer) Also participating (but not visible in the picture): Jean-Francois Pirard (ESO/4MOST Project Manager) Joar Brynnel (4MOST Project manager)
The 4MOST Wide Field Corrector being installed on the VISTA telescope (Credit: Allar Saviauk)
The VISTA telescope ready for its first light with 4MOST (Credit: Allar Saviauk)