A thousand eyes on the Universe: MOONS takes first look into the heart of the Milky Way

Groundbreaking instrument captures its first observations at ESO’s Paranal Observatory, launching a mission to map millions of stars and galaxies. 

The Multi-Object Optical and Near-infrared Spectrograph (MOONS) has achieved First Light at the European Southern Observatory’s (ESO) Very Large Telescope (VLT) at the Paranal Observatory in Chile.

MOONS is a powerful next generation spectrograph built by an international consortium led by the UK Astronomy Technology Centre (UK ATC) in Edinburgh, part of the UK’s Science and Technology Facilities Council (STFC).

This milestone marks the beginning of a new era in cosmic exploration, as the groundbreaking instrument prepares to survey millions of stars and galaxies and reveal how the Universe evolved over billions of years.

Dr Oscar Gonzalez, MOONS UK Principal Investigator and Head of Project Science and Strategy at UK ATC, said: “MOONS is the result of an extraordinary international effort. For years our scientists, engineers and technicians have worked together to overcome remarkable technological challenges and create an instrument of exceptional capability. For me, First Light is a celebration of their expertise, dedication and perseverance. It marks the exact moment in which years of work are transformed into discovery. MOONS will give astronomers an entirely new way of exploring the Universe, enabling observations that were simply beyond our reach, until now.” 

First observations

In astronomy, First Light marks the moment a new telescope or instrument successfully observes an astronomical target on sky for the first time. This milestone for MOONS represents the culmination of more than a decade of international collaboration involving engineering and science partners across the UK, Italy, France, Portugal, Switzerland, Chile and ESO.

For its first observation, MOONS displayed its transformative power by capturing the heart of the Milky Way in a new way: Being sensitive to near-infrared wavelengths, MOONS can peer through the dust that obscures our view towards the central regions of our Galaxy and beyond, providing an unprecedented spectroscopic view of this densely populated region.

A thousand eyes on the Universe

MOONS combines two unique capabilities: the ability to observe nearly 1,000 stars or galaxies simultaneously, while working over a wide range of wavelengths covering the visible and near-infrared light. These capabilities are enhanced by the 8-metre aperture of the ESO VLT, to make one of the most powerful spectroscopic facilities ever constructed.

MOONS is a spectrograph so doesn’t take pictures, instead it splits the light from stars and galaxies into detailed spectra. By analysing these spectra, astronomers can determine properties such as an object’s chemical composition, temperature, motion and distance. One observation can collect this information for nearly 1,000 objects simultaneously.

This is the first time this amount of data has been captured in a single observation.

By collecting and analysing light from millions of objects over its lifetime, astronomers will address some of astronomy’s biggest questions, from uncovering how the Milky Way formed and evolved to tracing the growth of galaxies across billions of years of cosmic history.

Extraordinary engineering

The instrument’s performance achieved during commissioning demonstrates the remarkable performance of its state-of-the-art optics, cryogenic systems and advanced control systems.

At the heart of MOONS is a remarkable feat of engineering. Now installed over 2,600 metres above sea level on the top of a mountain in Chile, the new instrument operates at cryogenic temperatures, with its optics and mechanism cooled to around 130 Kelvin (-140°C) and its detectors operating at approximately 40 Kelvin (-230°C), to reach the stability and sensitivity needed to detect the faintest light from distant galaxies and stars.

To achieve this, MOONS uses a giant cryostat believed to be the largest ever built for a ground-based astronomical telescope. Equally impressive is MOONS robotic fibre positioning system: a masterpiece of precision engineering that places 1,000 optical fibres onto their celestial targets with micrometre accuracy, allowing astronomers to survey the sky on a scale and efficiency never before possible.

Celebrating a major milestone 

Professor Michele Dougherty, STFC Executive Chair and UK Astronomer Royal, travelled to Chile to join the UK ATC team to witness First Light. She said: “Seeing MOONS achieve First Light was tremendously exciting. A landmark moment, not only for the international team behind this remarkable instrument, but for astronomy as a whole. It demonstrates the transformational science that innovative instrumentation can deliver.

“MOONS is also a powerful example of the UK’s world-leading expertise in astronomical technology and of STFC’s commitment to ground-based astronomy. Through investment in cutting-edge facilities and by enabling ambitious international collaborations, we are ensuring that UK scientists and engineers remain at the forefront of discovery, helping to answer some of the biggest questions about our Universe.”

Michele Cirasuolo, MOONS Principal Investigator and ESO Instrumentation Programme Manager, also said: “It is truly emotional to see the first light of MOONS, a remarkable achievement born from the extraordinary dedication and talent of an exceptional team.”

“MOONS opens a new window onto the Universe, allowing us to explore the physical, chemical, dynamical and environmental properties of millions of stars and galaxies across more than 13 billion years of cosmic history. It will take us to new frontiers in our understanding of how the Milky Way and galaxies have formed and evolved with time. I am incredibly proud of the team and hugely excited to see what new discoveries and new horizons in our understanding of the Universe lie ahead.”

New era of discovery

MOONS is expected to become a cornerstone instrument for the VLT, delivering vast spectroscopic datasets that will complement observations from facilities including ESA’s Gaia mission, the Vera C Rubin Observatory and future space missions.

With First Light now achieved, the MOONS team will continue commissioning and calibration activities before beginning full scientific operations. These initial observations already demonstrate the enormous potential of this next-generation instrument and mark the beginning of an exciting new chapter in astronomical exploration.

The MOONS instrument was designed and built by a consortium of universities and research institutes in Europe and Chile, namely:

• Science and Technology Facilities Council’s UK Astronomy Technology Centre (UK ATC), United Kingdom (consortium lead)
• Centro de Astro-ingenieria UC (AIUC), Pontificia Universidad Catolica de Chile, Chile
• ETH Zürich, Switzerland
• Galaxies, Etoiles, Physique et Instrumentation (GEPI), Observatoire de Paris-PSL CNRS, France
• INAF, Italy
• Institute of Astronomy (IoA), University of Cambridge, United Kingdom
• Instituto de Astrofísica e Ciências do Espaço (IA), Portugal
• Université de Genève, Switzerland