Want a workout? Try walking to the top of the world's largest telescope (photo)

The world's largest telescope continues to take shape on the Cerro Armazones mountain in Chile's Atacama Desert.

In a recent update describing the progress of the construction of the Extremely Large Telescope (ELT), the European Southern Observatory (ESO) shared a photo of the dome that will protect the telescope, which appears almost fully outfitted in its protective metal exterior. According to an ESO statement accompanying the photo, the dome is so large that it will take quite a while to walk from its entrance up to the top.

"If you want to take the stairs and walkways from the entrance of the ELT's dome all the way up to the top, you need about 30 minutes," ESO wrote in the statement. "Now that's what we call a workout!"

The angle of this new progress photo captures the altitude structure beneath the 135-foot (41-meter) wide roof opening. The dome structure has large sliding doors that will remain closed during the day and open at night, allowing the telescope to survey the sky.

There's a reason the dome is so big: It is designed to protect the massive telescope's mirrors. Standing more than 164 feet (50 meters) tall, the tube-like altitude structure will connect the 128-foot (39-meter) primary mirror, M1 — the largest telescope mirror ever made — to the 14-foot (4.25-meter) secondary mirror, M2, hanging above it and the central tower below.

These mirrors will allow astronomers to peer into the cosmos like never before. "The light it collects from the cosmos will bounce off to the secondary mirror, which will be held in the central ring seen at the very top of the picture," ESO officials said in the statement. "Light will then travel down again through the ELT's central tower and its three additional mirrors, before it reaches the scientific instruments that will be located at the side of the telescope."

Once complete, the telescope will hunt for Earth-like exoplanets in search of signs of life outside of our own solar system and probe the early universe to study the first galaxies that formed after the Big Bang, among other tasks.

The ELT will be the world's largest visible- and infrared-light telescope and is expected to see its "first light" by 2028. With the dome's frame completely built, the ESO is now working to install the multi-layered cladding that will insulate and protect the telescope from the harsh Chilean desert environment.

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

It turns out a comic visitor swept past the construction site of the world's largest telescope to check in on the structure's progress. In another recent photo update from ESO, comet C/2023 A3 (Tsuchinshan-ATLAS) can be seen streaking across the pre-dawn sky appearing as a "great white arrow" just above the horizon, illuminated by the soft glow of sunrise.

The comet's visit was captured on Sept. 30, 2024. Its bright coma and dusty tail can be seen to the left of the ELT.

Comet C/2023 A3 (Tsuchinshan-ATLAS), referred to by some as the "comet of the century," is a long-period comet with an 80,000-year orbit around the sun and believed to originate from a shell of icy bodies located on the outskirts of our solar system, known as the Oort Cloud.

The comet was initially discovered in 2023 and made its closest approach to the sun in September 2024. It was primarily visible to the naked eye for viewers in the Southern Hemisphere and the Tropics until about Oct. 9, 2024. It has since faded from view and headed out on its long journey back home.