From Mountaintop Telescopes to Space Observatories

Opened in 1904 in the San Gabriel Mountains, its 100-inch Hooker Telescope was the largest in the world from 1917 to 1949, and it was there that Edwin Hubble identified galaxies beyond the Milky Way and published the 1929 distance-redshift relation.

Operating from 1949 in the Palomar Mountains and run by Caltech, it is home to the 200-inch Hale Telescope, and its 48-inch survey telescope found the dwarf planet Eris, which helped prompt the 2006 redefinition of a planet.

Starting in 1970, this cluster of observatories on a dormant Hawaiian volcano used high altitude, dry air and dark skies to host telescopes from several countries, while its development remains opposed by some Native Hawaiians who regard the summit as sacred.

Launched in 1990, Hubble sits in low Earth orbit above the distortion of the atmosphere, observes in ultraviolet, visible and near-infrared light, and had a mirror flaw that a 1993 Space Shuttle servicing mission corrected.

Launched in 1999 and named for Subrahmanyan Chandrasekhar, it observes X-rays that Earth's atmosphere absorbs, from a high elliptical orbit, and is sensitive to sources 100 times fainter than any earlier X-ray telescope.

Launched on 25 August 2003 as the third of NASA's Great Observatories, it watched in infrared light from an Earth-trailing solar orbit until 2020, and in 2016 revealed five of the seven known TRAPPIST-1 planets.

Operating from 2008 in low Earth orbit and formerly called GLAST, it studies gamma-ray sources such as pulsars and gamma-ray bursts, and in 2010 announced two gamma-ray and X-ray emitting bubbles around the Milky Way.

Launched in 2009, Kepler used a single photometer to monitor the brightness of about 150,000 stars, searching for the small dips caused by planets crossing in front of them, and retired in 2018 when it ran out of fuel.

Operating from 2022 near the Sun-Earth L2 point, about 1.5 million km from Earth, Webb has an 18-segment hexagonal mirror and observes from long-wavelength visible light through mid-infrared, reaching galaxies closer to the early universe than any earlier telescope.