The largest optical telescope in the world

When building astronomical telescopes bigger is often better. And this means that there's often a race to build the next big telescope that will push our view of the Universe further and deeper. But before we obsess about the next big thing, lets take a moment to consider the current holder of the World's Largest Optical Telescope crown, the Gran Telescopio Canarias, which has a mirror stretching 10.4 m from side to side!

The Gran Telescopio Canarias on the summit of La Palma
(Credit: GTC)

The GTC, as its usually known, is the largest optical telescope in the world. It's based at the Roque de Los Muchachos Observatory at the summit of the island of La Palma, an excellent site for astronomy as it is both high up (above the clouds) and also very dry. It's owned and operated by several astronomical institutions in Mexico, the United States, and primarily Spain.

The 10.4 m mirror of the Gran Telescopio Canarias,
made up of 36 hexagonal, smaller mirrors
(Credit: GTC)

The telescope's mirror isn't a single mirror but 36 hexagonal mirrors that fit together to produce a telescope with an equivalent diameter of 10.4 m. Thanks to their extremely precise alignment all the segments reflect light as if they were a single mirror. This is a common technique in astronomy for making really big telescopes, as it is a lot easier to make multiple medium-sized mirrors than one very large mirror. As you'd imagine for a telescope of this size, the GTC took over 6 years to build!

The telescope was completed in 2008 and saw its first scientific observations in 2009. Since then the telescope has done some amazing work in all areas of astrophysics using a selection of instruments, including both imaging cameras and spectrographs, that can operate throughout the optical, the near-infrared and the mid-infrared.

The telescope sits close to the summit of La Palma at a site well known for its dry weather and good observing conditions. There are many telescopes clustered together at the observatory here, owned and operated by astronomical institutions across Europe.

I've had the pleasure of visiting this observatory many times for work and it is a beautiful place, well worth visiting if you get a chance, and particularly if you can stay for sunset (or get up early enough for sunrise!).

Sunset view from the summit of La Palma showing the Gran Telescopio Canarias (right) and the
Italian Telescopio Nazionale Galileo (left) above the clouds (Credit: Nick Wright)

Rehearsals aren't just for the theatre

We all know that actors rehearse, but did you know that telescopes rehearse as well? Large telescopes and surveys often rehearse the process of choosing targets, observing, and analysing the data so that they can be well prepared for the real thing.

Its a process that is particularly relevant with large surveys where efficient scheduling of observations is necessary to observe as many targets as possible in the time available. Modern telescopes also produce an incredibly large amount of data, sometimes many terabytes per night, and transferring this data from the telescope to different universities, and then processing and storing it all can be quite a mammoth task! Practising this process in advance allows potential issues to be identified and ensures that when the telescope is up and running the process proceeds smoothly.

The William Herschel Telescope
(Credit: Wikimedia Commons)

Most of the last month of my time has been spent preparing for an "Operational Rehearsal" for the WEAVE spectrograph being built for the William Herschel Telescope in the Canary Islands. This is quite an endeavour, as we're simulating over a week of observations on the telescope, which requires everyone involved to produce simulated target lists and spectra for them.

The goal of this work isn't just that the telescope operators and survey team will be able to experience the day-to-day running of the survey, its also so that the survey science teams become familiar with the process of supplying targets for the observations.

And so for the last month I've been busy simulating "fake" target lists, preparing "fake" spectra for those targets, and assembling everything into the format needed by the survey organisers and telescope operators. Its been quite a task, but hopefully it'll be useful for everyone involved in the survey to have gone through this rehearsal and learnt from it.

Big data from new telescopes

I read an article recently on the Guardian's science website called Big universe, big data, astronomical opportunity. The article discussed the rise of large datasets in science, particularly in astronomy, and the need for astronomers to adapt to the challenges faced by this by acquiring new skills for analysing such data.

The Large Synoptic Survey Telescope
(Credit: LSST)

The article made many good points about the rise of big data. We are, after all, on the verge of a number of large projects that will produce more data than we've ever seen before. These include the Gaia satellite (which I've talked about before), new sub-mm and radio telescopes such as ALMA and the Square Kilometre Array, and the Large Synoptic Survey Telescope. The latter is particularly noteworthy because once it enters operation in 2022 it will produce 30TB of data each night, more than most telescopes produce in a year!

Astronomers will need to learn not just to manage these datasets, but to effectively sort through and process them. New algorithms will need to be designed, utilising artificial intelligence and advanced machine learning methodologies, as well as new approaches to visualise and understand the results. Astronomers will have to embrace this because this is the way science is going, and the telescopes that will produce this data are already being built, or in some cases are coming online as we speak.

Despite making these good points the article then appears to suggest that these new telescopes and satellites, designed to answer the most far-reaching questions humanity has ever asked, aren't what we need. "Have we leaned all that we can from the data that we have?", the author asks, suggesting that we should analyse all the data we have before collecting more. The article even suggests that the data we have could "hold answers to some of the fundamental questions of the Universe we are seeking".

I strongly disagree with the author on this point and find this attitude rather short-sighted. The data that we have may provide answers to some questions, but certainly not the big questions we want to answer, and that's where we should be investing our efforts. We won't find answers in our existing data to questions such as how the Sun and the Earth formed, how the Universe began, or whether there is life out there, it's just not possible.

Astronomical research is the continuous pursuit of answers to the greatest questions we can ask. We usually can't answer these questions in one go so instead we answer them step-by-step, performing experiment after experiment, refining the question as we go. For each experiment we design the equipment needed to answer the question, and then when that question has been answered we take the research further. If the same equipment or telescope can be used to answer the next question then we use it, but often the next question involves looking further, deeper and at different wavelengths, requiring new telescopes and equipment.

Just because a lot of data already exists doesn't mean that the answers to our questions can be found there. The great explorers of the past didn't discover new continents by searching around at home, they built great ships and went in search of discovery. Astronomers shouldn't be searching around in old data, but building great telescopes and searching the skies for their discoveries!