New Giant Telescopes Are About To Rock Astronomy

When the Hooker Telescope first peered into the heavens in 1917, no one could predict the discoveries it would enable. Within ten years, Edwin Hubble used this 100-inch instrument—the largest telescope on Earth at the time—to show that galaxies exist beyond the Milky Way and that the universe itself is expanding.

A similar breakthrough occurred in 1949 when the 200-inch Hale Telescope captured its first images of the night sky. By the early 1960s, Maarten Schmidt employed the Hale to investigate unusual “quasi-stellar radio sources,” now known as quasars. These turned out to be supermassive black holes consuming matter at the cores of distant galaxies—a concept unimaginable when the telescope was built.

By the 1990s, technological advances enabled observatories to construct telescopes 8 to 10 meters in diameter. Alongside the 2.4-meter Hubble Space Telescope orbiting above Earth’s distorting atmosphere, these instruments analyzed a handful of faraway Type Ia supernovae—the explosive deaths of white dwarf stars. Researchers were astonished to find that the universe’s expansion is accelerating, a revelation only possible thanks to the capabilities of these new telescopes.

Today, astronomers are on the brink of another revolution in telescope design. Over the coming years, three new observatories, each more than twice the size of their nearest competitors, will begin scanning the skies. A fourth, slightly smaller at 8 meters, will employ advanced technology to photograph the entire visible sky every three days.

These four instruments promise groundbreaking science on many key questions. Yet, as with previous leaps in telescope size, they are likely to uncover phenomena that no one currently anticipates. As Pat McCarthy, vice president of the Giant Magellan Telescope (GMT) Organization, notes: “We expect to learn things we don’t know.”

Bigger mirrors, better views

Astronomers constantly push to observe fainter objects with higher detail. Larger telescopes collect more light, allowing astronomers to peer deeper into the universe. Doubling the diameter of a telescope’s primary mirror quadruples its surface area and light-gathering power. Observations that once required hours can be done in a fraction of the time, and the same mirror enables astronomers to see roughly twice as far.

The Las Campanas Observatory in Chile will feature a telescope effectively 24.5 meters across, made by combining seven mirror segments—roughly ten times the size of Hubble. Even so, there are limits to how much detail can be obtained. Hubble’s Frontier Fields program pushed close to those boundaries by capturing images of galaxies only a few hundred million years after the Big Bang. For nearby objects, Hubble still delivers unmatched clarity despite its modest size.

Astronomers rely not only on images but also on spectra, which break light into its component colors. Spectral analysis reveals an object’s temperature, composition, velocity, and rotation, and is essential for distinguishing stars from gas clouds or faint nearby stars from distant galaxies. Gathering sufficient light for spectroscopy takes far longer than imaging, so larger telescopes dramatically reduce observation times.

A telescope’s resolution improves with mirror diameter. Doubling the mirror’s width doubles the detail that can be resolved. Smaller telescopes can also achieve similar gains by linking their light through interferometry, a technique used by radio astronomers to capture the first image of a black hole in M87 from 54 million light-years away.

Ground-based observatories face the challenge of Earth’s turbulent atmosphere, which blurs light as it passes through layers of air at different temperatures. That’s why large telescopes are placed atop high mountains, reducing the amount of atmosphere between the mirror and space. Even temperature differences between the inside and outside of the observatory dome can create air currents that reduce image sharpness.

Adaptive optics addresses this problem. These systems use a thin, flexible mirror controlled by a computer to counteract atmospheric distortion in real time. A bright reference star near the target object allows the computer to measure blurring and adjust the mirror shape up to 1,000 times per second. When no suitable star exists, astronomers can create one using powerful lasers projected into the upper atmosphere.

Crafting giant mirrors

Before telescopes can operate, their enormous mirrors must be constructed. One method involves casting a single monolithic mirror. University of Arizona astronomer Roger Angel pioneered this approach around 1980. Glass chunks are heated to 2,100 degrees Fahrenheit in a spinning furnace, where they flow into a parabolic shape ideal for focusing starlight. Mirrors are kept lightweight with a honeycomb structure and polished to precise specifications. The Richard F. Caris Mirror Lab has created mirrors for the 6.5-meter MMT Observatory and the twin 8.4-meter mirrors of the Large Binocular Telescope.

The second approach, developed by astronomer Jerry Nelson in 1977, uses multiple hexagonal segments joined into a single mirror. The Keck telescopes in Hawaii, for example, each have 36 segments measuring six feet across. The Gran Telescopio Canarias in Spain employs a similar segmented design.

Next-generation observatories

The Vera C. Rubin Observatory will be the first of the new generation to begin operations. Its 8.4-meter Simonyi Survey Telescope is notable not for sheer size but for rapid, wide-field imaging. Located atop Cerro Pachón in Chile, it can capture a 9.6-square-degree portion of the sky—the equivalent of 40 full moons—in just 15 seconds.

The Rubin Observatory will capture more than 800 images per night using six color filters, producing a “digital color movie” of the universe. Its 3.2-gigapixel camera, the largest digital camera ever built, weighs over 6,000 pounds and spans 5.5 by 9.8 feet. Images are compared in real time to detect changes, generating up to 10 million alerts per night for transient events like supernovae and enabling a comprehensive census of small solar system bodies.

The Giant Magellan Telescope (GMT) in Las Campanas will use seven 8.4-meter mirrors arranged in a flower-like pattern to achieve an effective aperture of 24.5 meters—roughly ten times Hubble’s size. With four mirrors installed, the GMT will already surpass all existing telescopes and is expected to reach completion by 2028. Located 8,248 feet above sea level in the Atacama Desert, the GMT will provide unparalleled views in visible and near-infrared light.

The Extremely Large Telescope (ELT) and the Thirty Meter Telescope (TMT) take a segmented approach. The ELT’s primary mirror will contain 798 hexagonal segments, producing a 39-meter aperture, while the TMT will combine 492 segments for a 30-meter aperture. The TMT, situated on Mauna Kea in Hawaii, will allow astronomers to observe the entire northern sky. Construction has faced challenges due to the mountain’s cultural significance, but a legal ruling in 2018 cleared the way for first light in 2026.

Revolutionary science

These new giant telescopes will transform astronomy. They will study Earth-like exoplanets, revealing atmospheric composition and weather patterns. They will observe star formation, track brown dwarfs, and capture supernovae across the universe with unprecedented detail. Central regions of galaxies and star clusters will be resolved more clearly than ever, and early galaxies and their supermassive black holes can be examined to understand cosmic evolution.

These instruments will also help address fundamental questions about dark matter and dark energy and may clarify discrepancies in measuring the universe’s expansion rate. Working alongside the James Webb Space Telescope, the next decade promises profound insights into the structure and evolution of the cosmos—though, as history has shown, new telescopes are sure to uncover mysteries we have yet to imagine.