Infrared telescope

Lore & Background

Key developments led to the invention of the infrared telescope. In 1800, William Herschel discovered infrared radiation. In 1878, Samuel Pierpoint Langley created the first bolometer, a sensitive instrument that could electrically detect small temperature changes in the infrared spectrum. Thomas Edison used his tasimeter to measure heat in the Sun's corona during the solar eclipse of July 29, 1878. In the 1950s, scientists used lead-sulfide detectors cooled with liquid nitrogen to detect infrared radiation from space. Between 1959 and 1961, Harold Johnson created near-infrared photometers that allowed measurement of thousands of stars. In 1961, Frank Low invented the first germanium bolometer, cooled by liquid helium, which led the way for current infrared telescope development.

Infrared telescopes may be ground-based, air-borne, or space telescopes. They contain an infrared camera with a special solid-state infrared detector that must be cooled to cryogenic temperatures. Ground-based telescopes were the first used to observe outer space in infrared, with popularity increasing in the mid-1960s. However, water vapor in Earth's atmosphere absorbs infrared radiation, so ground-based telescopes are placed on high mountains and in very dry climates. In the 1960s, scientists used balloons to lift infrared telescopes to about 25 miles (40 kilometres) up. In 1967, infrared telescopes were placed on rockets, the first air-borne infrared telescopes. Later, aircraft like the Kuiper Airborne Observatory (KAO) were adapted, and in May 2010, NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA) placed a 17-ton infrared telescope on a Boeing 747 jet airplane, built with United States and German scientists.

Reader's Guide

Placing infrared telescopes in space eliminates interference from Earth's atmosphere. One of the most significant infrared telescope projects was the Infrared Astronomical Satellite (IRAS), launched in 1983, which revealed information about other galaxies and the center of the Milky Way. NASA's James Webb Space Telescope (JWST), launched on December 25, 2021, is a solar-powered spacecraft with an infrared telescope currently in space. The article lists notable ground-based telescopes including the Infrared Telescope Facility (1979–), Gornergrat Infrared Telescope (1979–2005), Infrared Optical Telescope Array (1988–2006), United Kingdom Infrared Telescope (1979–), and Wyoming Infrared Observatory (1977–). Airborne telescopes include the Kuiper Airborne Observatory (1974–1995) and SOFIA (2010–2022). Space-based telescopes include IRAS (1983), Spitzer Space Telescope (2003–2020), Herschel Space Observatory (2009–2013), Wide-field Infrared Survey Explorer (2009–2024), Nancy Grace Roman Space Telescope, James Webb Space Telescope (2021–), and Euclid (2023–). The legacy of infrared telescopes is their ability to detect radiation from all celestial objects above absolute zero, overcoming atmospheric absorption through ground-based, airborne, and space platforms.

Did You Know?

• The first bolometer was created by Samuel Pierpoint Langley in 1878.
• Frank Low invented the first germanium bolometer in 1961, cooled by liquid helium.
• The James Webb Space Telescope was launched on December 25, 2021.

Engineering a Mirror for the Infrared

The James Webb Space Telescope's primary mirror stands as one of the most ambitious optical systems ever built for space. Rather than a single polished disc, it is assembled from eighteen individual hexagonal segments of beryllium, each coated in a thin layer of gold to maximize infrared reflectivity and then sealed under a delicate glass layer for durability. Together these segments form a 6.5-meter aperture, yielding a light-gathering surface of roughly 25 square meters—more than six times the collecting area of Hubble's 2.4-meter mirror. Despite this enormous mirror, Webb's overall mass is only about half that of its predecessor. A critical engineering constraint is thermal: the entire telescope must remain below 50 kelvin so that its own thermal emission does not drown out the faint infrared signals it is trying to capture. To achieve this, a five-layer sunshield blocks heat from the Sun, Earth, and Moon, keeping the optics in a permanently cold environment while the spacecraft orbits a million and a half kilometers from home.

Why Infrared Unlocks the Early Universe

Webb's scientific power stems from its ability to observe wavelengths between 0.6 and 28.5 micrometers, spanning red visible light through the mid-infrared. This range is not arbitrary. The most distant and ancient objects in the cosmos have their original visible light stretched by cosmic expansion into the infrared, making them invisible to telescopes like Hubble, which tops out near 2.5 micrometers. Infrared radiation also penetrates dense dust clouds far more readily than shorter wavelengths, revealing star-forming regions and planetary systems hidden from visible-light observers. Colder bodies—debris disks, exoplanets—radiate most strongly in these same bands. The practical payoff is extraordinary: Webb can resolve objects roughly one hundred times fainter than Hubble and peer back to redshift z≈20, roughly 180 million years after the Big Bang, an era when the first stars were just igniting. Hubble's practical limit sits near z≈11.1. Beyond pure cosmology, Webb can also track Solar System bodies at angles greater than 85 degrees from the Sun and respond to transient events like supernovae within 48 hours.

From Concept to Orbit: Two Decades of Persistence

The telescope now known as JWST began life in 1996 under the working title Next Generation Space Telescope. By 1999, two concept studies had been commissioned with an eye toward a 2007 launch and a budget of roughly one billion dollars. Reality proved far more demanding. The program endured what its own history describes as enormous cost overruns and schedule delays, culminating in a sweeping redesign in 2005. Construction was not finished until 2016, after which years of exhaustive testing followed before the spacecraft was finally cleared for flight. The total price tag swelled to approximately ten billion dollars. On 25 December 2021, an Ariane 5 rocket lifted the telescope from the Kourou spaceport in French Guiana. By January 2022 it had settled into a halo orbit around the Sun–Earth L2 Lagrange point, roughly 1.5 million kilometers beyond Earth. The public first saw its science payload in action when the inaugural full-color image was released on 11 July 2022, marking the culmination of more than a quarter-century of planning, engineering, and political negotiation.

A Three-Nation Endeavor and a Name from the Apollo Era

Although NASA spearheaded the design and development of the telescope, the project was never a single-agency effort. The European Space Agency and the Canadian Space Agency served as central partners, contributing instruments and expertise that made the full scientific payload possible. Day-to-day development was managed by NASA's Goddard Space Flight Center in Maryland, while operational control and science operations are handled by the Space Telescope Science Institute, located on the Homewood campus of Johns Hopkins University in Baltimore. The primary industrial contractor was Northrop Grumman, which oversaw the build of the spacecraft. The telescope carries the name of James E. Webb, who served as NASA administrator from 1961 to 1968—the period encompassing the Mercury, Gemini, and Apollo programs. His tenure helped establish the agency's culture of ambitious, long-horizon exploration, a spirit that the infrared observatory now carries forward a generation later. As the largest telescope ever placed in space, it represents a collective achievement spanning three national space programs and a global scientific community.