From ESOblog: “A date with a formidable science machine”

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From ESOblog

20 September 2019

On the Ground

ESO’s Very Large Telescope (VLT) is the world’s most advanced optical and infrared astronomical observatory and observes objects four billion times fainter than the naked eye can see. But what is it like to spend a night deep in the Atacama Desert observing the stars with the VLT? How does it feel to control such a machine? Cyrielle Opitom, an ESO Fellow resident in Chile, describes one of her shifts observing the night sky with this formidable machine.

Cyrielle Opitom

15:00, 21 August 2019

My workday starts at 3 pm, after a quick breakfast and a visit to the gym. I use one of the observatory cars to drive from the astronomers’ hotel — the Residencia — up to the control room, which is located next to the telescopes and allows us to control them remotely. Contrary to what people might think, the astronomers at Paranal Observatory don’t always work entirely at night. Several of us actually work partly during daytime and partly during nighttime. This allows us to work on projects related to the instruments hosted on the telescopes here, assist visiting astronomers, or prepare observations for the coming night, for example.

Tonight, we have a visiting astronomer coming to observe with the Very Large Telescope’s (VLT’s) ESPRESSO instrument for the first part of the night. When I arrive at the control room, I make sure that everything is ready for the visitor’s observations, and have a look at what could be observed during the second part of the night, when we will work in service mode, performing observations on behalf of astronomers not present at Paranal. In total, about 60–70% of the observations are made in service mode, and about 30–40% in visitor mode.

Tonight, I am in charge of the VLT’s third Unit Telescope — UT3, also known as Melipal. At the moment, the UT3 is equipped with only one permanent instrument: SPHERE. However, ESPRESSO can be used with any VLT Unit Telescope, and is often used with UT3.

ESO SPHERE extreme adaptive optics system and coronagraphic facility on the extreme adaptive optics system and coronagraphic facility on the VLT MELIPAL UT3, Cerro Paranal, Chile, with an elevation of 2,635 metres (8,645 ft) above sea level

ESO/ESPRESSO on the VLT, installed at the incoherent combined Coudé facility of the VLT. It is an ultra-stable fibre-fed échelle high-resolution spectrograph (R~140,000, 190,000, or 70,000) which collects the light from either a single UT or the four UTs simultaneously via the so-called UT Coudé trains


At 4 pm, I go to the daily meeting with the various engineering teams (mechanics, electronics, optics, IT, software…). During the meeting, we discuss the state of all the telescopes and instruments to make sure that they are ready for the night and we also plan for the next day.

After the meeting, it is already time to go back down to the Residencia for some dinner before the night starts. Days are short in winter! After dinner, I head back to the control room.


It’s sunset time! There is never a boring sunset here at Paranal.


Now that it’s dark, it’s time to start observing. To operate the telescope and the instruments, we are sitting at the UT3 console, inside the control room. In general, we need two people to operate one telescope: one astronomer and one Telescope and Instruments Operator (or TIO). The astronomer is in charge of selecting the observations, operating the instrument, and assessing the quality of the data, while the operator is in charge of the telescope itself. Tonight is a bit special and there are four of us at the telescope. I am the support astronomer, Nestor is the TIO, Rosita is a new astronomer-in-training, and we have a visiting astronomer. In visitor mode, the visiting astronomer decides what they want to observe, and the astronomer and TIO execute the observations and check the quality of the data.

The VLT Unit Telescope 3 console, from which astronomers control the telescope and its instruments.
Credit: ESO/Cyrielle Opitom
The screens on the left of the image allow us to control the telescope and are operated by Nestor. In the centre, you can see the control panels for the SPHERE instrument, while ESPRESSO’s are on the right.

Tonight, we are observing several stars using ESPRESSO to try to detect or characterise exoplanets around them; ESPRESSO is specialised at hunting for rocky exoplanets. The observations are short, so that approximately every 30 minutes we command the telescope to point in another direction to observe a different star. The instructions on how to execute the observations are prepared by the visitors, and stored in what we call an “observing block” using dedicated software. We then use another piece of software to send the instructions to the telescope and instrument system and execute them in sequence. Being in the control room, it is very easy to forget that you are controlling such a large telescope. But every time I remember this, I feel both excited and amazed by the fact that I am the one observing with the VLT.


Cyrielle admires the night sky above one of the VLT Auxiliary Telescopes.
Credit: ESO/Cyrielle Opitom

I decide to go out onto the platform to admire the sky and the telescopes before the moon rises. The beauty of the night sky and the Milky Way never fails to amaze me. While the observations are being taken, and after checking the quality of the data obtained so far, we do some observatory-related projects.


It is 10 pm, and after several hours of hard work, it is time for a break. The cooks have brought some snacks into the control building meeting room, so we eat some bread, cheese, ham and fruit to give us the energy we need to get through the rest of the night.


The second part of the night has now started and we are in service mode. It’s getting late, but fortunately we have the coffee machine to help us stay awake for a few more hours!

In service mode, we use a dedicated tool to decide which of the numerous observations requested by astronomers around the world (and approved by a committee) are most suitable to perform depending on the weather conditions. For now this is another ESPRESSO observation.


We are now changing to the other instrument that we can use with the UT3 telescope: SPHERE. This instrument allows us to correct for atmospheric turbulence — which scatters light and makes images blurry — so that we can obtain the best possible images for a telescope of this size. SPHERE is often used to search for exoplanets, or to image disks around protostars. While performing the observations, I keep training Rosita on how to operate UT3 at night.


Finally my long day/night ends, and it is time to go to bed. Nestor, our TIO, will continue the observations of the night together with Rosita. Only 12 hours to go until my next shift starts!

Cyrielle (right) and astronomer-in-training Rosita (left) controlling the VLT’s SPHERE instrument.
Credit: ESO/Cyrielle Opitom

See the full article here .


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ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
•KUEYEN (UT2; The Moon ),
•MELIPAL (UT3; The Southern Cross ), and
•YEPUN (UT4; Venus – as evening star).
elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo,

Glistening against the awesome backdrop of the night sky above ESO_s Paranal Observatory, four laser beams project out into the darkness from Unit Telescope 4 UT4 of the VLT, a major asset of the Adaptive Optics system

ESO LaSilla
ESO/Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres.

ESO VLT 4 lasers on Yepun

ESO Vista Telescope
ESO/Vista Telescope at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level.

ESO/NTT at Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres.

ESO VLT Survey telescope
VLT Survey Telescope at Cerro Paranal with an elevation of 2,635 metres (8,645 ft) above sea level.

ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile. located at the summit of the mountain at an altitude of 3,060 metres (10,040 ft).

APEX Atacama Pathfinder 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert.