ELTs

ELTs, or extremely large telescopes, refer to a class of next-generation ground-based optical and near-infrared observatories characterized by very large primary mirrors and advanced adaptive optics. These features aim to provide greatly increased light-collecting power and much higher angular resolution than previous generations, enabling detailed studies of faint and distant objects, exoplanets, and the early universe. ELTs are typically defined by primary mirrors exceeding about 20 meters in diameter and rely on sophisticated adaptive optics to compensate for atmospheric distortion.

The European Extremely Large Telescope (ELT) is the flagship project associated with this class. Planned by the European Southern Observatory, the ELT is designed with a 39-meter segmented primary mirror and a comprehensive adaptive optics system to deliver high-resolution images across optical and near-infrared wavelengths. It is being constructed at Cerro Armazones in Chile. Other large telescope projects often grouped with the ELT class include the Giant Magellan Telescope (GMT) and the Thirty Meter Telescope (TMT), which aim to achieve comparable capabilities with 20–30 meter class apertures, though these projects have different design details and funding circumstances.

Scientific goals for ELT-class facilities span a broad range: direct imaging and characterization of exoplanets, detailed spectroscopy of exoplanet atmospheres, studies of galaxy formation and evolution, and investigations into the first stars and galaxies after the Big Bang. Instrument suites typically combine wide-field imaging, high-resolution spectroscopy, and integral field units, all supported by multi-conjugate adaptive optics to maximize stability and resolution.

Status: As of the mid-2020s, the ELT is under construction with first light anticipated in the late 2020s. GMT and TMT are progressing through design, funding, and construction phases with timelines subject to change.