- Courtesy of TMT International Observatory
- Artist's conception of the TMT showing the laser guide star adaptive optics system. The giant telescope is on track to become operational in 2029.
Say it quickly — "30-meter telescope" — and it doesn't sound like much. But this new $2 billion instrument under construction near the summit of Mauna Kea on Hawai'i's Big Island is a monster. Compare, for instance, the current record holder for optical telescopes, the 10.4-meter Gran Telescopio Canarias (located on Spain's Canary Islands) which has a light-collecting area one-eighth that of the TMT. A huge "light bucket" like this may well revolutionize astronomy by allowing us to see the first stars and galaxies, birthed soon after the Big Bang. And much more. "Expect the unexpected" might well be the motto of astronomers wanting to take full advantage of the new 'scope once it's up and running.
Seven sites were considered for the TMT, with the dormant volcano Mauna Kea coming out well ahead of the others. It's simply the best location on Earth for an optical telescope, combining as it does high altitude (13,290 feet, above most of the moisture in the atmosphere), pollution-free skies and ease of access for construction and operation. It's also in the northern hemisphere, so will be able to view those parts of the heavens inaccessible to an even larger telescope, the E-ELT, now being built in Chile by a European consortium.
All optical telescopes are plagued by atmospheric distortion, even at 13,000 feet. The solution, adaptive optics (aka "the poor man's Hubble telescope"), measures atmospheric distortion in real time by creating and monitoring a pseudo-star with a powerful laser that excites sodium atoms in the upper atmosphere. The distortion is then canceled out by continuously adjusting the shape of a telescope's mirror. The TMT's mirror actually consists of 492 thin (45 millimeter) hexagonal segments and each one will be actively controlled from the back hundreds of times a second by 21 acuators. The result will have the several hundred segments functioning as a single, continuously flexing mirror.
I held off writing this column until the state of Hawai'i had decided whether to allow construction to proceed. For several years, protestors have argued that the sacred nature of Mauna Kea should preclude siting a 14th telescope on or near its summit. A long and bitter court-driven process culminated on Sept. 28 with a 5-to-2 vote by the Hawai'i Board of Land and Natural Resources permitting construction to go ahead, with financial guarantees and many conditions, including that three older instruments on Mauna Kea will be decommissioned.
Not being a native Hawai'ian (and coming from the land of Captain Cook, whose 1778 landing on Kaua'i began a long and distasteful history of exploitation by outsiders), I'm not in a position to judge the decision. I can't help thinking, though, that the original settlers in Hawai'i, who nearly a thousand years ago used stars to navigate vast, featureless distances across the ocean from Tahiti and Samoa, might have appreciated the islands' unique role now in exploring the universe from arguably the best viewing platform on the planet.
Barry Evans (barryevans9@yahoo.com) notes that the TMT's mirror has 86,436 times the area of his backyard telescope.
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