Welcome, new life

For astronomers, broadening horizons literally means reaching for the stars. The European Southern Observatory (ESO) with its spectacular telescopes helps make this happen while demonstrating the allure of what lies beyond the discoveries.

For astronomers, broadening horizons literally means reaching for the stars. The European Southern Observatory (ESO) with its spectacular telescopes helps make this happen while demonstrating the allure of what lies beyond the discoveries.

The first things that visitors see are stars. Lots of them. At second glance, experts peering in immediately recognize the Andromeda Galaxy, spiral galaxies and the Magellanic Clouds. And of course, the Southern Cross. The view is simply stunning. At the European Southern Observatory’s (ESO) interactive center in Garching, outside Munich, the glass dome in the entrance area to the “Supernova” has a 14-meter diameter and weighs almost 30 metric tons. Approximately 262 glass panels have been meticulously arranged to depict several constellations found in the Southern Hemisphere. The dome magically conjures up constellations and simulates the Milky Way as it can only be seen from Chile; the area has been dubbed the “Void,” referring to how astronomers describe the empty space between two large structures. And there is lots of room to make new discoveries.

It has been a few weeks since the center held its opening in April. In an area that spans 2,200 sq. meters, installations covering 13 themes have been set up using multimedia formats to interact with the public. In an emotionally packed presentation, the center shows the knowledge scientists have been gaining over the years thanks to the ESO’s founding back in 1962. However, they also provide a clear indication of what the research goals are for the future. How are galaxies formed? Why do stars twinkle? Is there life beyond our solar system? Financed by donations and taxpayer money, the ESO counts 16 nations belonging to it. The new Supernova Planetarium and Visitor Center provide the organization with a unique opportunity to not only provide an outlet for the fascination and appeal of astronomical research, but to also make it comprehensible in layman’s terms how it impacts our daily lives. After all, generating advocacy and providing outreach to the public are almost as important for the ESO as discovering new black holes.

Visitors to the ESO’s Supernova can marvel at an ELT segment made of ZERODUR® glass-ceramic.

The choice of the Chilean night sky was obviously not random. Since 1979, the sole requirement of all work carried out by the ESO, which essentially functions as a service provider for science, has been the use of earthbound telescopes located in South America. Roughly 300 of the ESO’s 700 employees are continually on site in Chile. Visitors to the new center now have the possibility to step into the shoes of the astronomers who work there and experience the skies from their perspective. Since 1998, the Very Large Telescope (VLT) has been in operation in the Atacama Desert. Several photographs and astronomical visualizations in the ESO facilities were taken with the VLT. For the four main mirrors – each with a diameter of 8.20 meters – SCHOTT manufactured the largest monolithic glass components ever built. The individual telescopes can then be coupled to form a gigantic interferometer. “Astronomers almost always set the impossible as their goal,” notes Markus Kissler-Patig. He is a senior astronomer who has been involved as a scientist in the most spectacular ESO project of the last several years: the planning and building of the Extremely Large Telescope (ELT), which could be described as humankind’s largest eye. Beginning in 2024, and within sight of the VLT in Chile, the ELT is ready to take the field of astronomy to new levels of discovery.

“The sensors could pick up the growth of grass in real time.”

Until then, a lot of blood, sweat and tears will have been shed at the ESO because building the ELT is nothing short of an engineering masterpiece. “Literally everything we are doing has never been done before,” explains Program Manager Roberto Tamai. Kissler-Patig then adds, “We are essentially constructing a prototype, that has to be able to function immediately. And to achieve that, we find ourselves constantly pushing the limits of what is feasible.” Roughly 50 engineers and scientists from the ESO make up the ELT project team. When stepping into the Integration Hall, the incredible challenges the team faces are clearly visible, such as designing the instrument’s primary mirror, which is 39 meters in diameter. In this hall, using a prototype, the ESO is testing how seven original segments are constructed, maintained and managed so that the positioning accuracy is much smaller than the wavelength of light; a maximum tolerance of several nanometers only. The Herculean task is made more evident when you consider the performance capacity of the sensors under every segment. Eventually, they will allow up to 1,000 corrections per second on the mirror. “They are so powerful, they could theoretically register grass growing in real time,” explains Kissler-Patig.

In the ESO’s Integration Hall, the construction of the mirror segments for the ELT is put to the test.

“We don’t want to lose a single quantum of light.”

The primary mirror is made up of 798 ZERODUR® glass-ceramic segments. When you include maintenance and spare parts, SCHOTT is manufacturing a total of 949 round discs. The French company REOSC, the optical department of the SAGEM Group, is polishing and cutting them into hexagons. No similar feat has ever been achieved in the history of batch production of astronomical mirror substrates. The production of the components for the primary mirror gets underway in 2019 in the German city of Mainz. The casting and ceramizing processes take almost four months each to complete. In peak periods, one segment can be completed in a single day. “A project like the ELT would not be possible if a material with these properties did not exist,” says Kissler-Patig. “When it comes to the ELT, every step is about making pioneering efforts,” admits Jean-Louis Lizon, who supports the construction of the prototype and who also holds the ESO record for the most visits to Chile: Since 1981, he has come to the site in the Atacama Desert 132 times. Kissler-Patig is quick to point out what that piece of trivia reveals. Scientific work done at 3,046 meters above sea level is like “working on the moon.”

Nearly 200 individuals are busy at the VLT on the Cerro Paranal Mountain. The telescope is in operation every day of the year, 24 hours a day. A routine has been determined and is followed. At night, the four domes open up with two employees overseeing the observations. The next morning, the data is evaluated at the control center located beneath the summit. The data is made available to Garching almost simultaneously. While the evaluation takes place, specialists are busy preparing the telescope for the next night’s shift. For safety and security purposes, no one is allowed to work for more than two weeks at a time at the top of the mountain. The remoteness is a liability. Not to mention the 5 to 10 percent air moisture. It is dry as dust out here. The Cerro Paranal is an extreme environment to work in. Consuming liquids is crucial. Every day, tanker trucks fi lled with potable water leave the port city of Antofagasta some 120 kilometers away before making the grueling trip up the mountain. The VLT will only be connected to the electricity grid when construction is underway for the ELT. Once the sun has gone down, light comes as it did before – from a source very, very distant. The rays of light are billions of years away before they are received by the VLT and 2024 at the earliest by the ELT. Every quantum counts. “We don’t want to lose a single one,” says Kissler-Patig, who has spent many nights gazing into the Chilean skies. This much he knows: you simply have to have experienced the real thing; even if the simulation in the Supernova comes very close to replicating it.

Roberto Tamai, ELT Program Manager Extremely Large Telescope


The ELT’s construction is a masterpiece of engineering expertise. Nothing comparable to it has ever been built. Can you describe
some of the extreme challenges that you have faced during the years of planning and implementation?


“We are creating a piece of equipment weighing 5,000 metric tons. The spacing of the 798 segments on the primary mirror needs to be precisely set at no more than 2 nanometers (nm), and they must be movable. This is the equivalent to saying that the waves in the Atlantic Ocean are not allowed to be higher than the thickness of a euro coin.”

September 18, 2018


Dr. Thomas Westerhoff
Advanced Optics

More articles