Crystal-clear skies and perfectly dry air combine to make the Atacama Desert in Chile one of the best spots in the world to peer into the vastness of space. Light and other electromagnetic radiation can reach the ground with little interference from clouds or drops of moisture, creating optimal conditions for observation. For this reason, it's home to some of the most powerful telescopes on Earth.
One of these machines is Paranal, the largest optical-infrared observatory in the Southern Hemisphere in terms of light-collecting area. Operated by the European Southern Observatory (ESO), it contains the flagship Very Large Telescope (VLT) and two others, the VLT Survey and VISTA.
A fundamental principle when it comes to building telescopes is interferometry, which gives astronomers the ability to link multiple telescopes together, so that when they observe the same object simultaneously, they act as a single device, called an interferometer. The further the telescopes are placed apart, the better the quality of image they produce. This is why telescopes are often situated hundreds of metres apart – another reason why the barren desert is the perfect location for them.
The Paranal Observatory is a lonely place. The closest community consists of fewer than 300 people in a town called Paposo, 38 kilometres away. The observatory rarely attracts visitors without an astronomy degree. Photographer Benedict Redgrove visited the site for WIRED in 2017. This is the story of how observatory operates on a day-to-day basis.
The Yepun Unit telescope: This is the interior of Yepun, one of VLT’s four Unit Telescopes. The white structure in the centre is the cell, which supports the 8.2-metre-wide primary mirror. Attached underneath is SINFONI, an integral field infrared spectrograph that comprises two instruments working together: a spectrograph and an adaptive optics module. It can capture 3D images of any astronomical object it looks at, and has been used in a range of discoveries, from giant gas clouds being ripped apart to the most distant galaxy ever observed.
Auxiliary and unit telescopes: On the left is one of the 1.8-metre-wide VLT Auxiliary telescopes, and three of the four VLT Unit Telescopes. The Antu (“the Sun” in the indigenous Mapuche language) appears in the foreground, followed by Kueyen and Melipal (“the Moon” and “the Southern Cross” respectively). On the right is the Yepun VLT Unit Telescope. Acting together, these four telescopes, and four moveable Auxiliary Telescopes, use interferometry to see 25 times more detail than if they were operating on their own.
The Yepun Unit telescope: Yepun (“Venus” or “Evening Star” in Mapuche) is shown tilted, in preparation for its sunset opening. The black objects at the bottom of the image are laser launch telescopes, which shine lasers at night to create artificial “stars”. These are used as a reference for astronomers to see how much the atmosphere is blurring the images they are collecting, so they can create clearer pictures.
Horsehead Nebula: A composite colour image of the Horsehead Nebula, an interstellar cloud of gas and dust, and its immediate surroundings. It is based on three exposures in the visual part of the spectrum taken using the Kueyen Unit Telescope's FORS2 multi-mode instrument. The Horsehead Nebula was discovered by the Scottish astronomer Williamina Fleming in 1888, and can be found just south of the Belt of Orion.
Espresso Spectrograph: A member of the Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) team during the assembly and integration of the instrument. ESPRESSO is an extremely high-sensitivity spectrograph, designed to detect Earth-sized rocky planets orbiting other stars in our galaxy. It does this by searching for tiny, regular movements in stars caused by a planet orbiting it. These movements cannot be seen, but are presented in the form of changes in the light coming from the star, created by the Doppler effect. ESPRESSO only started working with all four telescopes in February 2018.
Muse: The Multi Unit Spectroscopic Explorer (MUSE) is an integral-field spectrograph installed in the Yepun telescope. It allows astronomers to examine the whole of an object in space at once and plots each pixel’s intensity as a measure of a spectrum of colours. MUSE splits what it can see into 1,152 slices, or mini-slits, and measures more than 4,000 colours. MUSE is used to study the early Universe, when galaxies were just starting to form, and to map dark matter in clusters of galaxies.
VLT And Omegacam: This image shows the cell supporting the primary mirror of the 2.6-metre-wide VLT Survey Telescope and the OmegaCAM imager attached underneath. OmegaCAM comprises 32 light sensors known as charge-coupled devices (CCDs). It can observe a one-degree-by-one-degree field of view, with 256 million pixels. The camera has two filters around a spectral line called H-alpha, the exact wavelength of light given off when an electron in a hydrogen atom is excited and then falls back down to its ground state. This means OmegaCAM is ideal for looking for hydrogen, which makes up a lot of the gas in nebulae and stars.
Auxiliary Telescope: A Panaral technician is shown moving one of the four 1.8-metre Auxiliary Telescopes along a system of train-track-like rails during a reconfiguration of the VLT’s interferometer. The telescopes can be relocated to 30 stations across the platform of the VLT. The telescopes are generally used separately, but they can be moved to a special configuration where all four work together to achieve a much more detailed picture of the Universe – with a resolution sharp enough to be able to see an astronaut on the Moon from Earth.
This article was originally published by WIRED UK
