April 22, 2014

Sutherland Sky: Part IV

Posted by Evelyn Mervine

The impressive looking SALT telescope, perched high on a Karoo hillside.

The impressive looking SALT, perched high on a hill in the Karoo.

Today I’m continuing with my series of posts about my October 2013 visit to the small town of Sutherland in South Africa’s Northern Cape province. Sutherland is home to a South African Astronomical Observatory (SAAO) research station that contains many telescopes, including the Southern African Large Telescope (SALT). You can read Part I of this series here, Part II of this series here, and Part III of this series here.

Today I’m sharing some pictures of SALT, the most famous telescope located in Sutherland. I don’t know much about telescopes, to be honest, so here’s some information from the SALT website:

The Southern African Large Telescope (SALT) is the largest single optical telescope in the southern hemisphere and among the largest in the world. It has a hexagonal primary mirror array 11 metres across, comprising 91 individual 1.2m hexagonal mirrors. Although very similar to the Hobby-Eberly Telescope (HET) in Texas, SALT has a redesigned optical system resulting in a larger field of view and effective collecting area.

SALT can detect the light from faint or distant objects in the Universe, a billion times too faint to be seen with the unaided eye – as faint as a candle flame would appear at the distance of the moon. The telescope and instruments are designed to operate from the near ultraviolet to the near infrared (320 to 1700 nm), and offer some unique or rare capabilities on a telescope of this size.

SALT is situated at the South African Astronomical Observatory (SAAO) field station near the small town of Sutherland, in the Northern Cape province, and is ~380 km from Cape Town.  SALT is funded by a consortium of international partners from South Africa, the United States, Germany, Poland, India, the United Kingdom and New Zealand. The construction phase was completed at the end of 2005 and from 2006 to 2009 it entered a period of commissioning and performance verification. Since September 2011, observing is now in full swing and the telescope is finally realising its huge potential as Africa’s Giant Eye on the Universe.

I definitely recommend checking out the SALT website. There’s much great information there although it does seem that some sections of the website, such as the “Picture of the Month”, have not been updated since 2011. However, there is a SALT blog that seems to be updated regularly. The blog has daily observation logs and the occasional post on topics such as optics and an astronomer’s braai (South African BBQ). There is also a website for scientists interested in working at SALT. This website provides information on how to apply for observation time at SALT. Since observation time at SALT is limited and sought after, there is an application / proposal process in place to allocate the observation time to various scientists. I also ran across this informative SALT webpage on the Rutgers University website. And here’s another great website about SALT.

During my weekend visit to Sutherland, I visited SALT and some of the other telescopes on the Saturday afternoon. SALT and the other telescopes are located a short drive away from the small town of Sutherland. The telescopes are perched on top of a hill away from the modest light pollution of the little town of Sutherland.

Here are some pictures that show the location of the telescopes on the hill:

The road from the town to the telescopes. You can make out the telescopes on top of the hill in the upper left.

The road from the town to the telescopes. You can make out the big SALT telescope in the upper left just below the power line.

Another view of the telescopes from the road.

Another view of the telescopes from the road. SALT is the biggest telescope on the left. Some pretty Karoo wildflowers are in the foreground.

All the telescopes up on the hill.

All the telescopes up on the hill. There’s some nice sedimentary bedding on the hill, too!

Here are some pictures of SALT up close:

SALT telescope viewed from the parking area.

SALT viewed from the top of the hill.

Another close-up view of SALT.

Another close-up view of SALT.

As part of the tour, I was able to visit the inside of SALT. Here’s a diagram showing what SALT looks like on the inside:

Annotated SALT diagram, taken from the Rutgers University website here: http://www.physics.rutgers.edu/ast/ast-salt.html.

Annotated SALT diagram, taken from the Rutgers University website here: http://www.physics.rutgers.edu/ast/ast-salt.html.

On the tour, I went past the Control Room, where I was able to see a scientist at work:

A scientist at work in the SALT control room.

A scientist at work in the SALT control room.

Then I went up the stairs to the Visitor’s Gallery, where I was able to take a look at SALT’s impressive mirrors:

SALT's impressive mirrors.

SALT’s mirrors.

I apologize for the poor quality of the above picture– it was difficult to take a good picture through the window of the Visitor’s Gallery. The gallery is kept separated from the mirrors by windows because it is important to keep conditions (temperature, humidity, etc.) perfectly controlled in the room with the mirrors.

Again, I’m afraid I don’t know much about telescopes, so here’s some information on SALT’s mirrors from Wikipedia:

Both SALT and HET have an unusual design for an optical telescope. Similar to the Keck Telescopes, the primary mirror is composed of an array of mirrors designed to act as a single larger mirror; however, the SALT mirrors produce a spherical primary, rather than the paraboloid shape associated with a classical Cassegrain telescope. Each SALT mirror is a 1-meter hexagon, and the array of 91 identical mirrors produces a hexagonal-shaped primary 11 x 9.8 meters in size. To compensate for the spherical primary, the telescope has a four-mirror spherical aberration corrector (SAC) that provides a corrected, flat focal plane with a field of view of 8 arcminutes at prime focus.

Each of the 91 mirrors is made of low-expansion Sitall glass and can be adjusted in tip, tilt and piston in order to properly align them so as to act as a single mirror. Because the mirror is spherical, light emitted from a position corresponding to the center of curvature of the mirror will be reflected and refocused to the same position. Therefore, the telescope employs a Center of Curvature Alignment Sensor (CCAS) situated at the top of a tall tower adjacent to the dome. Laser light is shone down on all the segments and the position of the reflections from each mirror measured. A process called “stacking” thus allows the telescope operator to optimize the adjustments of the mirrors.

SALT’s mirrors certainly look very impressive! To me, they look as if they belong in a science fiction movie or perhaps a James Bond movie… I can just see a James Bond villain taking over the world with SALT.

Speaking of science fiction, I mentioned in an earlier post that I visited SAAO and SALT as part of an event organized by a local (South African) Star Trek club to which I belong. Of course, if you attend a Star Trek club event, it’s best to attend in uniform. So, several of us wore Star Trek attire during our SAAO tour:

My husband Jackie and I in Star Trek: The Original Series uniforms in front of the SALT telescope.

My husband Jackie and I in Star Trek: The Original Series uniforms in front of the SALT telescope.

Four Trekkies in front of SALT.

Four Trekkies in front of SALT.

The human race may not (yet) be exploring The Final Frontier as part of the United Federation of Planets. However, at least we are looking up at the sky in places such as Sutherland.

That’s all for this post. Next, I’ll share some pictures of some of the other telescopes located at Sutherland. After that, I’ll share a few pictures highlighting the geology of the Karoo region in the vicinity of Sutherland.