List of largest optical reflecting telescopes

For the largest reflecting telescopes on the planet, the horizontal indicates the year built and the vertical direction indicates the size of the mirror measured in meters. Countries which contain several of these telescopes are color-coded for identification.

Sorted by aperture, which is a measure of the light-gathering power and resolution of a reflecting telescope.

- List of largest optical reflecting telescopes

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Large Binocular Telescope

"LUCIFER" redirects here.

LBT perched on an Arizona mountain
Dome during the day with doors closed
Interior looking down one of the primary mirrors
Computer systems for LBT
Computer workstation for LBT

The LBT mirrors individually are the joint second-largest optical telescope in continental North America, next to the Hobby–Eberly Telescope in West Texas.

W. M. Keck Observatory

Two-telescope astronomical observatory at an elevation of 4,145 meters near the summit of Mauna Kea in the U.S. state of Hawaii.

The Keck II telescope showing the segmented primary mirror
Mirrors of Keck Observatory
Keck Observatory closeup
Spectroscopic capabilities of Keck Observatory instruments as of late 2019. Instrument modes appear as color-coded boxes with spectral resolution (resolving power) and wavelength coverage. Non-spectroscopic (i.e. imaging-only) instruments are not shown.
Size comparison of primary mirrors

Both telescopes have 10 m aperture primary mirrors, and when completed in 1993 (Keck 1) and 1996 (Keck 2) were the largest astronomical telescopes in the world.

Extremely Large Telescope

Astronomical observatory currently under construction.

ESO Council meets at ESO headquarters in Garching, 2012.
ELT construction status, January 2022.
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The optical system of the ELT showing the location of the mirrors.
Cast of the first ELT main mirror segments.
ELT's M2 Mirror Blank.
ELT concept.
Size comparison between the ELT and other telescope domes.
The First ELT Instruments.
ELT compared to the VLT and the Colosseum
Artist's rendering of the ELT in operation.<ref>{{cite web|title=Artist's rendering of the ELT in operation|url=https://www.eso.org/public/images/eso1716a/|website=www.eso.org|access-date=29 May 2017}}</ref>
Diagram of the 40m-class ELT primary mirror.
ELT compared with one of the four existing VLT Unit Telescopes at Cerro Paranal, Chile
Rendering of ELT during the day.
Model of the gigantic and intricate structure inside the enclosure of the ELT.
Close-up of ELT primary mirror (artist's impression). <ref>{{cite web |title=Milestones Reached in Incredible Journey of ELT Main Mirror Segments. |url=https://www.eso.org/public/announcements/ann20009/ |access-date=11 February 2020 |language=en}}</ref>
Rendering of the MICADO instrument. <ref>{{cite web |title=ELT MICADO Instrument Passes Preliminary Design Review |url=https://www.eso.org/public/announcements/ann20002/ |website=www.eso.org |access-date=23 January 2020 |language=en}}</ref>
thumb|The night sky over the construction site for the Extremely Large Telescope.<ref>{{cite news|title=The Milky Way above the ELT sitey|url=https://www.eso.org/public/images/potw2011a/|access-date=16 March 2020}}</ref>

The observatory aims to gather 100 million times more light than the human eye, 13 times more light than the largest optical telescopes existing in 2014, and be able to correct for atmospheric distortion.

Segmented mirror

Array of smaller mirrors designed to act as segments of a single large curved mirror.

Size comparison of primary mirrors. Segmented mirrors are typically hexagonal and arranged in a honeycomb pattern.
Early segmented mirror, built out of 61 hexagonal segments in 1952.
SALT's segmented mirror
James Webb Space Telescope primary mirror assembly

Also known as the GranTeCan, the Canaries Great Telescope uses a total of 36 segmented mirrors. With a primary mirror of 10.4 m, it is currently the world's largest optical telescope, located at the Roque de los Muchachos Observatory on the island of La Palma, in the Canary Islands in Spain.

Large Zenith Telescope

6.0-meter diameter liquid-mirror telescope located in the University of British Columbia's Malcolm Knapp Research Forest, about 70 km east from Vancouver, British Columbia, Canada (north from Maple Ridge).

Comparison of nominal sizes of primary mirrors of the Large Zenith Telescope and some notable optical telescopes

It was one of the largest optical telescopes in the world, but still quite inexpensive.

List of optical telescopes

For the largest reflecting telescopes on the planet, the horizontal indicates the year built and the vertical direction indicates the size of the mirror measured in meters. Countries which contain several of these telescopes are color-coded for identification.

List of largest optical reflecting telescopes - List of large optical telescopes

European Southern Observatory

Intergovernmental research organisation made up of 16 member states for ground-based astronomy.

Directors general of ESO (from left to right): Lodewijk Woltjer, Harry van der Laan, Catherine Cesarsky, Tim de Zeeuw and Xavier Barcons
La Silla cluster of telescopes
The ESO 3.6 m Telescope
The New Technology Telescope
Dome of the Danish 1.54-metre telescope that has been in operation at La Silla Observatory since 1979.
A 360-degree panoramic view of the southern night sky from Paranal, with telescopes in foreground
The Very Large Telescope and the star system Alpha Centauri.
Globular Cluster 47 Tucanae
ESO science archive
Artist's impression of ESO Supernova Planetarium & Visitor Centre.
ESOcast is a video podcast series with the latest news and research in astronomy.
VISTA's infrared view of the Orion Nebula
The Helix Nebula
The Globular Cluster Omega Centauri
A 340-million pixel starscape from Paranal
NGC 2264 and the Christmas Tree cluster
The Centre of the Milky Way
NGC 2467 and Surroundings
The Horsehead Nebula
Messier 78: a reflection nebula in Orion
The WR 22 and Eta Carinae regions of the Carina Nebula
The hidden fires of the Flame Nebula
Early morning on Paranal
The future ALMA array on Chajnantor (artist's rendering)
Rare 360-degree Panorama of the Southern Sky
370-million-pixel starscape of the Lagoon Nebula
The Milky Way panorama
The Omega Nebula
Centaurus A
Glowing Stellar Nurseries
The R Coronae Australis region imaged with the Wide Field Imager at La Silla

It will use a 39.3-metre-diameter segmented mirror, and become the world's largest optical reflecting telescope when operational in 2024.

Gran Telescopio Canarias

10.4 m reflecting telescope located at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain.

Dome of the GTC at sunset.

It is the world's largest single-aperture optical telescope.

ESO 3.6 m Telescope

Optical reflecting telescope run by the European Southern Observatory at La Silla Observatory, Chile since 1977, with a clear aperture of about 3.6 m and 8.6 m2 area.

The ESO 3.6 backdropped by the southern sky, and annotated note for the recently discovered Nova Centauri 2013
The ESO 3.6-metre telescope.
The road to the telescope at La Silla.
Euler Telescope and the ESO 3.6 m Telescope (background).
Panoramic view of the ESO 3.6-metre telescope's dome.
La Silla—Early evening scenery (in the distant right: the ESO 3.6 m T.)
Construction of the ESO 3.6-metre telescope.<ref>{{cite news|title=Three Very Different Telescopes at La Silla|url=http://www.eso.org/public/images/comparisons/potw1219a/|access-date=8 May 2012|newspaper=ESO Picture of the Week}}</ref>
NGC 2207 and IC 2163, two interacting galaxies (captured by EFOSC2)
NGC 520, colliding galaxies

When completed it was one of the world's largest optical telescopes.

Palomar Observatory

Astronomical research observatory in San Diego County, California, United States, in the Palomar Mountain Range.

Palomar Mountain Observatory featured on 1948 United States stamp
Hale Telescope Dome
Hale telescope dome
Component of the Hale telescope
The now decommissioned 18-inch Schmidt Camera
Greenway Visitor Center at Palomar Observatory, with a gift shop

The 200-inch (5.1m) Hale Telescope was first proposed in 1928 and has been operational since 1948. It was the largest telescope in the world for 45 years.