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Visiting SALT: A Once in a Lifetime Opportunity

By Eric Brindeau,
This article was originally published in Canopus, October 2010 (PDF) - external link

Visiting SALT – short for South African Large Telescope – must be on your ‘bucket list’. Not only is it one of the largest optical telescopes in the southern hemisphere, but it’s also probably one of the most expensive and hi-tech refrigerators too.

South African Large Telescope
SALT, South African Large Telescope, Sutherland

Sitting atop a hill just a short drive from the Karoo town of Sutherland, the telescope dwarfs the other twelve on the site of the South African Astronomical Observatory. Chosen for its pristine, dark skies and stable weather patterns, Sutherland is rated as one of the best astronomical sites in the world because of the number of clear nights in a year. (Unfortunately, though, the night I visited was not one of them!) A Japanese study found that the area is seismologically one of the quietest in the world – a bizarre fact after learning about Salpeterkop, a 66 million year old volcano that can be seen nearby peeking between the telescope domes. Lying far from any major routes, visiting the observatory takes some effort, but for me it’s less of a detour.

A few years ago my parents retired to the outskirts of the sleepy seaside town of Gansbaai in the Cape, some four hours’ drive from Sutherland. My dad – a mechanical engineer, who like me is also fascinated by telescopes – planned our adventure while I was visiting in May this year. Invited on our trip were my friends Peter and Gwyn and their son, Sean Baxter, who also now live in the Cape. Peter was a long-time member of the society and won several awards at Scope-X for the beautiful wooden telescope he made in the ATM (Amateur Telescope Making) classes. Meeting up with them (and dog Scooter) in the equally sleepy town of Villiersdorp, we were ready to embark on our journey back in time.

Travelling on the N1 as far as Matjiesfontein, the scenery changes dramatically from the Cape Fold Mountains of the Hex River Valley to the vast desolation of the Karoo. From the N1 turn-off to Sutherland, the main road meanders between wide valleys and watercolour-smudged mountains in the distance. There was hardly a soul in sight for the 110km stretch. I continuously scanned the horizon for silhouettes of the telescope domes but even as we reached Sutherland, SALT was still not visible.

Entering the town, the only hint of its connection to the universe are signboards to B&Bs with extraterrestrial names like Galaxy, Jupiter and Galileo. Even the cluster of three antique refractors, permanently on display outside the information centre and painted dark green, must look like cannons to the uninitiated. I would not have needed a second glance had they been painted the traditional white. My first impression was that of a typical Karoo town: wide, tree-lined streets, the church steeple still the tallest structure in sight, hand-painted advertising signs and buildings that embody the history of its birth in the mid 1800s. But this town is relatively untouched by modern times. Vapour trails criss-cross the sky high above from the daily air traffic of the Joburg to Cape Town route. Most of the roads are still unpaved and there’s only a single petrol station and bank. After the B&B lady requested that we “just put the keys on the fridge when we leave”, I realised just how less carefree life has become back home. And fame of living near one of the top ten largest telescopes in the world – matched only by those in exotic locations like Chile and Hawaii – doesn’t seem to faze anyone.

I can imagine the countless professional astronomers and engineers passing through, students trekking here lucky enough to get jobs they can add to their CVs, as well as ordinary people whose forefathers would never have imagined them as tour guides or mechanics for a telescope. I wonder how many philosophical discussions have been debated in cafes, how many solutions to problems have been sketched on napkins or typed up on laptops over coffee in B&Bs, or how many new theories to the workings of the universe have been dreamed up here. Leaving for our tour, we were about to see what these explorers had already experienced.

Only after a couple of winding kilometres and a few uphills does the observatory come into view. SALT is breathtakingly enormous. I was looking at my first ’real’ observatory. I could see several white domes on the horizon, quite out of place on this alien landscape. Our first stop was the visitor centre, the telescopes still out of clear view higher up on the hill. Out of nowhere, several other enthusiasts arrived, as if summoned by SMS. The visitor centre has several exhibition rooms with interactive science displays. Huge photographs of galaxies and nebulae cover the walls. In one room there’s a massive iron meteorite that must be straining the building’s foundations. In another, several real fossils from fish to frogs are displayed behind glass showcases. After watching a cleverly made DVD on the astronomical scale of space – zooming out from a couple on a picnic blanket in Central Park to the edge of the known universe and back – our guide briefed us. We then drove in convoy up on top of the hill – past SALT – and parked near the smaller domes.

There’s a big international presence here – Germany, Korea, Japan, USA and UK – but strangely missing are the ubiquitous flags. The telescopes don’t seem to obey any master plan. They range in size from 1.9 to 0.5 metres, some with cool names like SuperWASP, MONET and BiSON. Unfortunately the 1.9 metre reflector (originally from the Radcliffe Observatory in Pretoria), which is normally part of the tour, was under repair. But there was no disappointment when we parked in front of SALT. Soaring 30 metres above us, I was struck by its clean architecture. No frills, everything with a purpose. To one side is a strange tower that upsets the otherwise symmetrical shape of the building. Like its twin – the Hobby-Eberly in Texas – I soon learnt it was not a cooling or exhaust vent of some sort, but the ’Mirror Alignment Tower’, which holds a laser system used to collimate the primary mirror. SALT’s 11 metre mirror consists of 91 hexagonal segments, each positioned under computer control to enable astronomers to collimate the primary accurately. Each segment is a metre wide and weighs about 100kg. To make the telescope project more feasible, the design was simplified by not allowing it to point freely in the sky, thereby avoiding more complex engineering, mirror distortions and the like. The scope is free to rotate on its base in azimuth, but is permanently fixed in altitude at 37 degrees and can only reach objects in a circular band 12 degrees wide at the zenith. The tilt was designed to include the Large and Small Magellanic Clouds. We entered the telescope dome, passed a windowed control room, climbed a staircase – greeted by several photographs on the walls of SALT being built – to finally see this 85 tonne achievement.

Engineer on Cherry Picker above the telescope mirror
Engineer working on SALT’s 11 metre mirror

While looking out the windows to admire the view on the way up, I could not help noticing how thick the walls are and was intrigued on learning why. Unlike many large telescopes that have hi-tech air ventilation systems, in order to equalise the temperature of mirror with that of the outside air, SALT is a giant fridge. The dome is well insulated and kept at the perfect temperature inside by massive air-conditioners. From our glass-enclosed viewing room, seeing the inner workings of the scope and ginormous mirror was an exhilarating moment. We were fortunate that our tour coincided with technicians doing maintenance on the mirror. An engineer carefully manoeuvred himself on a cherry-picker between the massive trusses – hovering precariously over the primary – to remove one of the mirrors for re-coating. Stepping back out into the bright sunlight, followed by the excited chatter of the group and walking far enough away from the dome to fill the frame for one last photo, we were almost ready to leave.

Turning back for one last glance, I could imagine this hilltop once witness to the receding ocean of the inland Karoo Sea some 250 million years ago. Home to mammal-like reptiles for 50 million years – the transitional stage between reptiles and mammals and pre-dating dinosaurs – this part of the Karoo provides a unique window of evolutionary history. Preserved in these rocks is a complete continuous fossil record for which South Africa is world renowned. But while the age of this area is staggering, it is nothing compared to how far back in time SALT can stare into space.