And yet it moves

Like a flower following the Sun, the dome of ESO’s Extremely Large Telescope (ELT) will be able to rotate to allow the telescope to track objects in the sky. Seen under the bright blue skies of Cerro Armazones in the Chilean Atacama Desert, this video shows a test of the dome rotating for the first time.

The test moved the dome 10 m in either direction at 1 cm/s, but the final operating speed will be a walking pace of 5 km/h. The test was performed by engineers of Cimolai, the company contracted by ESO to design and build the ELT dome and telescope structure. The humans hard at work in this sped-up video show, for scale, the sheer size of the telescope dome. Rotating the dome is no small feat, as its skeleton currently weighs about 2500 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 motorised 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 dome, in its final form, will have an insulated aluminum cladding to protect the telescope from the elements and sliding doors to open it to the stars. Building this marvel of engineering in the middle of the desert presents unique challenges, and yet, recent achievements such as the dome rotating and the first mirror segments stored at Paranal show the ELT is moving closer to becoming reality.