A 'giant' rising in the desert: World's largest telescope comes together (photo)

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The Extremely Large Telescope is currently under construction, with the most recent milestones including progress made with building the dome, central structure and the base for the primary mirror.

A metallic dome structure in the desert with sunlight making it look quite beautiful.
Recent progress photos of the European Southern Observatory's (ESO) Extremely Large Telescope (ELT) reveal its dome, central structure and base of the M1 mirror are taking shape. (Image credit: ESO/G. Vecchia)

Construction of the world's largest telescope moves forward with progress of the structure's dome and housing for the primary mirror.

The European Southern Observatory's (ESO) Extremely Large Telescope (ELT) — the world's largest visible- and infrared-light telescope — is currently under development on the Cerro Armazones mountain in Chile's Atacama Desert. The mighty telescope is expected to see its "first light" by 2028, with the goal of observing terrestrial exoplanets and their atmospheres, as well as measuring the expansion of the universe.

New photos from the ESO reveal that progress has really been made with construction of the ELT, including its dome, central structure and base of the M1 mirror — one of five mirrors that will work together to observe the cosmos.

The ELT "will be one of the main flagships of the European Southern Observatory for the next two decades," the ESO said in a statement releasing the new images.

Once complete, the M1 mirror will measure 128 feet (39 meters) across and weigh a whopping 200 tons. The white lattice structure shown in the center of the dome will hold the M1 mirror, allowing it to move smoothly during observations and compensate for varying gravity loads, wind conditions, vibrations, or changes in temperature.

On-site webcams, drone footage and photographs of the construction site allow for step-by-step progress updates of the ELT. In addition to the recent photos shared by the ESO, you can track development of the telescope through interactive webcam footage that streams live 24/7. The observatory also shared a time-lapse video of the construction site, with the warm glow of the sun rising over the optical telescope.

Related Stories:

— Could we turn the sun into a gigantic telescope?

— The Extremely Large Telescope: Facts about the world's largest telescope

— How the last 25 years led to the rise of mega-telescopes

If all goes according to plan, the anticipated development timeline for the ELT will see the telescope's secondary mirror (M2) completed in 2025. The 14-foot (4.25-meter) mirror — the largest convex mirror ever produced — will reflect light collected by M1 to the 12-foot (3.75-meter) tertiary mirror (M3), which has an estimated completion date in 2027. This mirror system will allow for better quality of observations over a larger field of view. The dome and telescope structure are on track to be completed by 2026.

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Samantha Mathewson
Samantha Mathewson
Contributing Writer

Samantha Mathewson joined Space.com as an intern in the summer of 2016. She received a B.A. in Journalism and Environmental Science at the University of New Haven, in Connecticut. Previously, her work has been published in Nature World News. When not writing or reading about science, Samantha enjoys traveling to new places and taking photos! You can follow her on Twitter @Sam_Ashley13. 

12 Comments Comment from the forums
  • brunodoggy
    At first glance, I thought someone was building a Death Star!
    Reply
  • damnyankee36
    ..."The 14-foot (4.25-meter) mirror — the largest convex mirror ever produced — will reflect light collected by M1 to the 12-foot (3.75-meter) tertiary mirror (M3)"...

    Wouldn't Mount Palomar's 200", (16.7'), mirror beat the size of the 14' secondary mirror of the ELT?
    Reply
  • George²
    damnyankee36 said:
    ..."The 14-foot (4.25-meter) mirror — the largest convex mirror ever produced — will reflect light collected by M1 to the 12-foot (3.75-meter) tertiary mirror (M3)"...

    Wouldn't Mount Palomar's 200", (16.7'), mirror beat the size of the 14' secondary mirror of the ELT?
    Well, it's easy when you compare the size of a primary mirror to the size of a secondary mirror. In this sense, today the main telescope at the Palomar Observatory is surpassed by about 20 telescopes. If we count only telescopes with a non-segmented mirror, then the Hale telescope is only 15th in the ranking of mirror sizes.
    Reply
  • DrDave
    damnyankee36 said:
    ..."The 14-foot (4.25-meter) mirror — the largest convex mirror ever produced — will reflect light collected by M1 to the 12-foot (3.75-meter) tertiary mirror (M3)"...

    Wouldn't Mount Palomar's 200", (16.7'), mirror beat the size of the 14' secondary mirror of the ELT?
    The 200" mirror on Mount Palomar is not a convex mirror but a concave one.
    Reply
  • Marc2001
    Will it outperform the JWST?
    Reply
  • DrDave
    Marc2001 said:
    Will it outperform the JWST?
    Well its horses for courses there. It has sufficient collecting area that you'll be able to do things like spectroscopy of the atmosphere of planets at nearby stars. Something JWST can't really do as well, however JWST which is above the atmosphere and all the distortions it brings will be unmatched in terms of the sort of high resolution images it will be able to get.
    Reply
  • starman2
    I wonder why it even needs a secondary mirror. At that size (14') you could easily position a human observer at the focal point of the primary mirror for the best undistorted viewing. But if they are also talking about a tertiary mirror (3.75 m) then they must mean some type of catadioptric design which gives a greater focal length. But nowhere in the article is any mention of catadioptric, Cassegrain, or Schmidt.
    Reply
  • damnyankee36
    DrDave said:
    The 200" mirror on Mount Palomar is not a convex mirror but a concave one.
    Duh, I didn't catch that... Thanks.

    Still, they are comparing two solid mirrors. I really don't know if the convex design makes a difference in the difficulty in manufacturing.
    Reply
  • billslugg
    The focal length of the primary mirror is 743.4 meters. Such a large structure would be hard to make.
    Reply
  • starman2
    I adjusted my viewpoint. Although the ELT is not completed yet, it is obviously a catadioptric design. For a reflector, the truss would be too extended, too heavy, and too expensive - but maybe not impossible. Catadioptric bounces the incoming light back and forth to achieve a long focal length. Long focal lengths mean high power - they're trying for exoplanets.
    Reply