The Largest Telescope in the Northern Hemisphere Is Being Built: It Will Revolutionize Sky Observation

With its 30-meter-diameter mirror, the Thirty-Meter Telescope will be the largest telescope in the Northern Hemisphere. On Earth, it is second only to the Extremely Large Telescope. It is expected to begin scientific activity in 2033.

Thirty-Meter-Telescope
Rendering of the Thirty-Meter Telescope dome. Credit: TMT Observatory Corporation.

In the overview of the largest telescopes currently under construction, we discuss the Thirty-Meter Telescope (TMT). While the Extremely Large Telescope (ELT), being built in the Chilean Andes, is the largest ever built, the TMT will be the largest in the Northern Hemisphere.

The Observation Site

The TMT will be built in the Hawaiian Islands, at the summit of Mauna Kea, at an altitude of 4,050 meters above sea level.

Mauna Kea offers the best visibility conditions (i.e., it is subject to less atmospheric turbulence), has lower atmospheric water vapor (essential for infrared and mid-infrared observations), and benefits from its high altitude.

Since the atmospheric thickness above (which absorbs and weakens the light from observed objects) is lower, the amount of light reaching the telescope is greater.

The observatory that will host the TMT will be the TIO – Thirty-Meter Telescope International Observatory. The members of TIO include the California Institute of Technology, the University of California, Japan’s National Institutes of Natural Sciences, the Department of Science and Technology of India, and the National Research Council of Canada. The Association of Universities for Research in Astronomy is an associate member of TIO. Most of the funding comes from the Gordon and Betty Moore Foundation.

It is worth noting that Mauna Kea, due to its exceptional observational qualities, is already home to other major telescopes, such as Keck I and II with 10-meter mirrors, Subaru with an 8.2-meter mirror, and Gemini North with an 8.1-meter mirror.

Characteristics of the TMT

The TMT will have a primary mirror 30 meters in diameter, made up of 492 hexagonal segments (mirrors) of 1.4 meters each, assembled to form a single reflective surface.

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The dome, resembling a giant eye scanning the sky, will house the telescope, whose mirror will act as the retina. Credit: TMT Corporation.

The most effective technique today for producing large-diameter mirrors is to build them as a collection of multiple segments, typically hexagonal in shape, like the cells of a large beehive. Because they are small, they have low thermal inertia.

In addition, each segment is connected to mechanical actuators (called active optics) that ensure the mirrors are perfectly aligned with each other to form a single smooth surface, with no discontinuities between adjacent segments.

The TMT will be the largest telescope in the Northern Hemisphere.

With its dimensions, the TMT will be the largest telescope in the Northern Hemisphere and, thanks to the size of its mirror, it will achieve image resolutions 3 to 4 times higher than those obtained by the James Webb Space Telescope.

The Dome

Despite the size of the mirror, it was possible to design a dome that minimizes its overall dimensions.

The dome designed to protect the telescope resembles a large eye, where the opening would be the cornea and the telescope acts as the retina. Its dimensions will be 55 meters high and 65 meters in diameter.

The telescope will be equipped with state-of-the-art instruments for imaging and spectroscopy observations.

The Science Behind the TMT

The scientific questions the TMT will tackle are numerous.

With unprecedented detail, the TMT will allow us to study the features of protoplanetary disks where exoplanets form. Credit: ESO/L.

It will conduct observations to understand the nature of dark matter and dark energy; it will explore the birth and evolution of the first galaxies; and investigate the relationship between supermassive black holes and their host galaxies. It will also delve into stellar astrophysics: the birth of stars, the search for exoplanets, and the study of their atmospheres for so-called “biosignatures,” or indicators of possible life.

Valuable contributions will also be made to the study of our Solar System: comets, asteroids, moons, and more.

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