The Extremely Large Telescope’s Dome is on the Move

Construction of the Extremely Large Telescope (ELT) reached a milestone, with the structure of the dome completed just enough where engineers were able to rotate the dome’s skeleton for the first time.

ESO released a timelapse video this week of the dome’s movement, sped up from the actual snail’s pace of 1 centimeter per second. When the telescope is completed – currently set for sometime in 2028 — the rotation of the dome will allow the telescope to track objects in the night sky over the Chilean Atacama desert. The final operating speed will be at pace of 5 kilometers per hour.

Take note of the size of the humans moving about on the video. They appear like tiny ants compared to the immense size of the aptly named ELT.

ESO used the phrase “and yet it moves” in the video. That phrase comes from an apocryphal tale about Galileo Galilei, when he was forced to recant his stance that the Earth revolved around the Sun – as opposed to the stance of the Catholic Church, which held that Earth was an unmovable firmament. Legend has it that after his forced recantation, he muttered, “E pur si muove” (“And yet it moves”), meaning Earth. This tale has been refuted, but it is still a good story, and perhaps a portrayal of Galileo’s stubborn attitude about the importance of intellectual freedom.

ESO said the test was performed by engineers of Cimolai, the company contracted to design and build the ELT dome and telescope structure. The skeleton of the dome currently weighs about 2,500 tons, and will eventually weigh around 6100 tons when finished.

“This first test was carried out “manually” with special hydraulic devices, but eventually the enclosure will rotate via motorized bogies. While the motion of the dome is designed to be smooth, and was found to be during this test, the dome stands separate from the rest of the structure in order to limit vibrations to the telescope itself.”

The ELT will be the world’s largest optical/near-infrared telescope, located on top of a mountain named Cerro Armazones in the Atacama Desert of northern Chile.

This artist’s impression shows the European Extremely Large Telescope (E-ELT) in its enclosure. The E-ELT will be a 39-metre aperture optical and infrared telescope. ESO/L. Calçada

It will consist of a reflecting telescope with a 39.3-meter-diameter (130-foot) segmented primary mirror, with 798 hexagonal elements that all work together. It also has a 4.2 m (14 ft) diameter secondary mirror. The observatory aims to gather 100 million times more light than the human eye, 13 times more light than the largest optical telescopes, and be able to correct for atmospheric distortion with adaptive optics and eight laser guide star units, and will have multiple science instruments.

The ELT will search for extrasolar planets, with the goal of detecting water and organic molecules in protoplanetary discs around stars in the making to help answer fundamental questions about planet formation and evolution. Scientists also hope to study the formation of the first objects in the Universe such as primordial stars, primordial galaxies, and black holes. Another goal of the ELT is the possibility of making a direct measurement of the acceleration of the Universe’s expansion.

See ESO’s website for more information about the ELT.

Nancy Atkinson

Nancy has been with Universe Today since 2004, and has published over 6,000 articles on space exploration, astronomy, science and technology. She is the author of two books: "Eight Years to the Moon: the History of the Apollo Missions," (2019) which shares the stories of 60 engineers and scientists who worked behind the scenes to make landing on the Moon possible; and "Incredible Stories from Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos" (2016) tells the stories of those who work on NASA's robotic missions to explore the Solar System and beyond. Follow Nancy on Twitter at and and Instagram at and

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