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SALT—Imaging the southern sky

When South Africa decided to build a new telescope, it went big. As in rival-the-world's-best big. With the participation of astronomy groups from all over the world, the Southern African Large Telescope, or SALT, is casting a wide eye on the southern sky. Moreover, it's inspiring future astronomers in the region. This Science Bulletins feature takes you behind the scenes as this bold new telescope brings world-class astronomy to a developing nation. Created by American Museum of Natural History.

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Video transcript

Telescopes are really very simple things. They collect light. They work in a way a bit like the human eye. And you can imagine a telescope as a giant eye. The bigger the telescope, the more light it can collect and the further it can see. And it really is just as simple as that. So if you could build a very big telescope, you can see very faint sources, and you can see very distant sources. Sources at the very edge of the Universe. Things from which the light has taken over 12 billion years to get to us. SALT is the Southern African Large Telescope. It’s the biggest single optical infrared telescope in the Southern Hemisphere. And I think what’s so important about the project is that it is an international collaboration. It allows us to work with people from the United States, from Europe, from India, and to bring those resources together to study the exciting things you can only see from the Southern Hemisphere. For people like me, who love our continent, SALT could be a focal point for development of scientific research in the continent, the African continent. Because we have this fantastic first-world, first-class facility that can attract astronomers and people who want to do astronomy in the whole African continent or just in South Africa. SALT is built in Sutherland. And the location was chosen because there was already another observatory existing there. Therefore, there was also infrastructure there. I mean, you didn’t have to go and start building an observatory from scratch. OK, home in back again to 240, please. Nicola (?), we’ll move to 240. This is the heart of the telescope, the primary mirror array, which consists of 91 individual mirror segments in a spherical configuration. This is equivalent to a mirror that would be 11 meters by 10 meters in size. Building something 11 meters in size is just, at the moment, technically impossible. So instead, we’ve made it up from a mosaic of individual segments that collect the light and focus it up to the instrument at the top of the telescope. At the moment, we have two science instruments on the telescope. One of them is an imaging camera—very similar to a video camera—which is used to make observations of varying phenomena, where the light is varying for one reason or another, possibly on quite short time scales. So this camera can take up to 10 frames a second. And so for things that are rapidly varying, that’s an ideal sort of instrument. The other instrument is a spectrograph, which splits up the light into component colors and then analyzes what we call the spectra of an object. And so, with that instrument, you’re able to probe a lot of detail and get a lot of physics out by looking at galaxies and stars and so on. In any given night, we will be observing many different objects from many different programs, which is quite different to the normal, classical way of scheduling telescopes, where an astronomer might get a telescope to themselves for one or two nights. OK, that should bring it to focus. All right, track time, hour and a half. Going straight through the central supply rate, [indistinct]. All right, SALTICAM is back on track. Say, half an hour from now, extending 45 minutes from that time on. I query the database, and it gives me several programs which are visible at that time. In this case, it’s only two targets. One is looking at galaxies from our Israeli collaborators. And there’s another target looking for Kuiper Belt objects. These are small bodies, celestial bodies on the outskirts of the Solar System. So we use SALT for science from, in astronomy, basically from one end to the other. We can look to the very, very distant Universe, and we can look at stars in our own galaxy. But then there are programs also which look at objects inside our own Solar System. Here’s an example of an observation we made recently of asteroids. These were 10-second exposures. See the asteroid moving over here? So every frame is one SALTICAM frame from the telescope. And we just put it together, and you see the object moving over there. There’s been a lot of science which has hinged around having this camera, that could take very, very fast observations. And then with the spectrograph, we were able to do quite a lot of very interesting observations of some colliding galaxies. One bit of research which we just recently finished was a galaxy we’ve been calling the “Bird Galaxy” because it looks like one. There was a surprise that the whole thing was supposed to be only two galaxies. But for the first time, really resolved, this—what we call the head of the bird—it really is a galaxy of its own. Everything which is blue over here is new stars being born. And on the other hand, the red bits are very obscured regions. There’s a lot of dust inside. So with SALT, what we did, we got a spectrum, the bright things are actually emission lines. This is actually hydrogen. And these two are nitrogen lines. And further on, you see sulfur. And then was sodium, and oxygen, and all those. They are twisted. Means that their velocities are different. So this part of the spectrum is actually moving away from us. And this part of the spectrum, well, it’s coming towards us. So when you map now this structure, on the image what we have, you can build an understanding of how this thing is moving. The Universe is a very dynamic place. Everything is moving with respect to everything else. And it’s very useful to have a tool to measure that movement. As an astronomer, it’s fantastic because I have now access to one of the largest telescopes in the world. So the type of science that I can do is just so much increased. It’s just so many possibilities. SALT is a focal point for development of science, research, and technology in South Africa. With SALT, we can motivate young people to want to take up careers in science. And with SALT, we will be able to come up with exciting discoveries that, you know, they give people a good feeling. You know, when you know that there’s some good things happening in your country.