A 39-metre telescope is now rising from the Atacama Desert in Chile, and it will collect more light than all existing large telescopes combined. This is the Extremely Large Telescope (ELT), a fundamental science facility that will transform nearly every branch of astronomy. Its sheer size—18 times the collecting area of Europe’s current largest telescopes—combined with adaptive optics that sharpen images five-fold, will let astronomers see details that are currently impossible. The ELT will directly image planets around nearby stars, search for molecules linked to life in exoplanet atmospheres, and map individual stars in galaxies millions of light-years away. It will also probe dark matter in the early Universe and test whether fundamental physical constants vary across space and time. The UK ELT Programme coordinates British contributions to the telescope’s instruments, including leadership of HARMONI, one of the two first-light cameras and spectrographs. UK groups are also building the high-resolution spectrograph for the METIS instrument and contributing to design studies for future instruments HIRES and MOSAIC. This is curiosity-driven research with no immediate practical application—but past fundamental astronomy has yielded technologies from wireless communications to medical imaging sensors.
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The Extremely Large Telescope (ELT) is now under construction in the Atacama Desert in northern Chile by the European Southern Observatory (ESO). With a diameter of 39m and a greater collecting area than all current large telescopes combined, the sensitivity and spatial resolution of the ELT will dwarf those of existing facilities in the visible and infrared. With the first observations planned for 2024, the sheer sensitivity of the ELT is truly remarkable, with a collecting area over 18 times that of ESO's current largest telescopes. The telescope will also continuously correct the light from astronomical objects with a technique called adaptive optics, giving astronomers images with five times better resolution than possible today. This vast step forward in both collecting area and image resolution from the ELT will be transformative for nearly every aspect of contemporary astronomy, from searches for molecules potentially linked to life in nearby exoplanets, out to detection of the most distant galaxies at the edge of the observable Universe. It will give us our first detailed views of individual stars in galaxies which are millions of light-years beyond the Milky Way, and help to settle arguments as to whether some of the fundamental constants of physics vary in space and time. It will have the capabilities to directly detect mature planets similar to those in our Solar System around nearby stars, while also probing the distribution of elusive dark matter in galaxies when the Universe was just 10% of its current age. This is just a small subset of the diverse and profound scientific breakthroughs we expect from the ELT, and UK astronomers and engineers are playing leading roles in the development of the cameras and spectrographs that will take the valuable observations in the mid 2020s and beyond. Building on a decade of scientific and technical development, the UK ELT Programme coordinates the UK roles in ELT instrumentation. At the core of the programme is leadership of the design and construction of the HARMONI instrument, one of the two first-light instruments for the telescope, ensuring UK astronomers will be well prepared to reap the rewards from ELT observations as soon as possible and some of its first discoveries. The programme also includes smaller roles in future instruments, so that UK astronomers can exploit as much as possible of the tremendous new discovery space of the ELT. The UK is building the high-resolution spectrograph for METIS, the third instrument for the ELT, now in construction (led by the Netherlands). UK groups also have key roles in design studies of the next instruments, HIRES (led by Italy) and MOSAIC (led by France), both of which will be essential to exploit the huge scientific opportunities of the observatory. Lastly, the programme is investing in research and development of new technologies that will influence the design of future ELT instruments, particularly the development of the PCS instrument for studies of exoplanets.
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