Turning the telescope

Exploring behind-the-scenes of Chile’s Very Large Telescope

In this first installment of our series on ESO’s Cerro Paranal site, This is Chile takes you on a backstage tour of the world’s most advanced optical instrument. 

Wednesday, January 16, 2013 Category: Education - Technology
Inside the Very Large Telescope. Photo by ESO/José Francisco Salgado. Inside the Very Large Telescope. Photo by ESO/José Francisco Salgado.


The European Southern Observatory’s Very Large Telescope (ESO VLT) is the world’s most advanced optical instrument, and thanks to the Atacama Desert’s clear skies, high altitude, and low light pollution, it’s also the most productive ground-based astronomy facility on the planet.


But how does the VLT really work? To find out, This is Chile headed deep into the Atacama for the first installment of our behind-the-scenes at Cerro Paranal series, “Turning the Telescope”.


Behind the VLT


While it’s easy to imagine astronomers peering into an enormous VLT eyepiece each night, the VLT is actually comprised of eight separate telescopes - four large Unit Telescopes each about the size of an eight story building, and four smaller Auxiliary Telescopes. These instruments can all function together as one unit, or be used separately for individual observations.


Data collected by these telescopes is sent to a large system of powerful computers in the VLT’s Control Room, where ESO astronomers work around the clock to ensure that the equipment is running smoothly.


About 10 astronomers are at work in the Control Room at any given time. During night shifts, astronomers examine the data being received from the VLT to make sure observations are being executed as planned. On day shifts, the team double-checks that observations went correctly the night before, and prepares the telescopes for what’s to come that night.


The VLT targets different objects in the universe each night - but these objects are generally not selected by the astronomers in the Control Room. Instead, astronomers from around the world submit specific project proposals to ESO, and the best projects are selected for research time.


Setting up the VLT


In addition to astronomers, the VLT requires a large team of dedicated engineers to keep the telescopes working properly, including specialists in instrumentation, software, electronics, and optics.  


Nicolas Haddad has been on the instrumentation team at Cerro Paranal for the past 10 years. It’s his job to start up one of the large Unit Telescopes each evening, and make sure the equipment is ready for the night’s observations.


Turning on the VLT is a multi-step process. Haddad first walks around the entire telescope, giving the equipment a visual inspection for potential hazards or complications.


Next, the telescope is moved into position for the night’s research. While weighing around 430 tons - about the weight of a fully loaded jumbo jet - the VLT rests on hydrostatic oil-firm bearings, allowing it to be moved nearly effortlessly.


“It’s amazing how the telescope moves,” Haddad told This is Chile. “If its brakes were removed, you could move it with your hand.”


The final step is opening the VLT’s massive dome. The dome features special ventilation windows that automatically regulate wind flow inside the telescope, preventing external elements from interfering with equipment.


As the sun sets over the Atacama Desert, the VLT is now fully ready to begin a night of exploring the distant Universe.


Coming up next in our “Turning the Telescope” series, we’ll take you behind the scenes at the Residencia, the state-of-the-art hotel that VLT astronomers call home.


By Liz Rickles

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