The Gran Telescopio Canarias (GTC) – for now, the largest single optical telescope on Earth – will host its own inaugural party next week.

The primary mirror of the GTC – named for its location in the Canary Islands, the Spanish archipelago off the coast of Morocco – consists of 36 hexagonal segments, just like the twin Keck telescopes in Hawaii. However, the GTC’s primary measures 10.4 m across, 40 cm bigger than the 10-m Kecks, and it has 75.7 square meters of light-gathering area.

Presumably, the GTC also takes advantage of the latest advances in active optics and adaptive optics since the Keck telescopes saw first light in the mid-1990s. “Active optics” is the system that keeps the primary mirror segments and the secondary mirror aligned despite changes in air temperature, the pull of gravity due to the telescope’s orientation and so forth. “Adaptive optics” lessens the optical aberrations caused by the atmosphere above the telescopes.

Next year the CanariCam, featuring innovative mid-infrared optics (wavelengths of 7.8 to 24.5 µm), will go into operation on the GTC.

The GTC won’t be the world’s largest single telescope for very long. As recounted in OPN’s July/August 2009 cover story, the Giant Magellan Telescope, now under construction, will feature seven primary mirror segments for a total aperture 25 m across. And even that instrument may be eclipsed by other huge telescopes that are now in the planning stages, such as the Thirty Meter Telescope.