Slashdot Mirror
SALT Telescope First Light
carnun writes "On the 1st of September, 5 years after ground breaking, the SALT Telescope released their first light images to the public. Yesterday one of these images was even displayed on NASA's Astronomy Picture of the Day website. The Southern African Large Telescope, built in South Africa, is the largest telescope in the Southern Hemisphere and (depending on how you define it) the equal largest telescope in the world, but built at a budget of only $30 million, about a tenth cheaper than its nearest competitor. The official opening of the telescope is scheduled for the 10th of November, but scientific observations are already a regular occurence. (Disclaimer: I'm the software engineer responsible for the main telescope server.)" Perhaps as an added bonus carnun could even be persuaded to participate heavily in the discussion. Either way, sounds like a cool project to be a part of.
Check the MirrorDot page, the original server is already smoking...
-- It's always darker before it goes pitch black.
Large telescopes are always compared by the diameter of their main mirror (or what would be the equivalent diameter in case of a more complicated design).
It's not correct to say "ten times cheaper" either. Once should say "one tenth the price" or something like that.
It is based on the diameter of the primary mirror (~10m for SALT). The equal is the prototype which SALT is based on, the HET in Texas (I think). Resolution depends on diameter so it would also have the best resolution, but the Earth's atmosphere tends to distort things too much. This is why the Hubble Space Telescope (which is a mere 2.4M) is so valuable - no atmospheric disturbance.
However, having a giant mirror means that the telescope can observe faint objects in less time than anything in space at the moment, so can take much higher resolution spectra.
The actual telescope can't use the whole mirror at once because of the design. The telescope only moves in azimuth, which saves a huge amount of cost but means that only a small part of the mirror is used at any one time. As the target rotates around the sky the area on the telescope moves across the mirror to allow longer exposures.
SALT also has very high sensitivity to short wavelengths (blue/UV) which is probably the best of any large telescope, or at least close.
Usually comparisons are based on mirror diameters, so SALT is roughly equal to Keck One or Two, the 10m mirrors on Hawaii. But if you're looking for sharpness of image, then you might be more interested in baselines, where interferometry allows configuration of multiple mirrors to achieve sharper images (by cancelling out interference and unwanted signals), such as the VLT in Chile. Baselines at the VLT can reach 200m, which makes the 10m mirror not quite as impressive.
To put it in slashdot-friendly terms, you shouldn't just compare processors based on clock speed, because different processors may be optimized for different purposes. Mirror size is kind of like clock speed.
One of the big reasons is that SALT's primary mirror is spherical. This means that each of the segments are of exactly the same design. A parabolic mirror, like that used on most other telescopes you general have to have different design for many of the segments. Downside - spherical mirror bring aberations. Upside - they can be compensated for quite by secondary mirrors.
The SALT primary consists of 91 segments each of which cost $30000, compare this to the estimated cost of having a single 10m primary ~$1 000 000 000.
Cheap (but highly skilled) engineers do help and then the last contributing factor is that the mirror is fixed in elevation - spherical mirrors mean that this the telescope is not limited to fixed elevation though.
- Carnun, Son of Danu -
"Existentialism lead to nihilism. Nihilism lead to dancing"
Tube-type first-gen NV was invented by the Germans in WW2. Americans fielded a rudimentary type for a sniper rifle, but it was cumbersome and not useful.
"Besides, what fool would waste time and resources trying to take "nearby" photos of a place we've already been when the telescope can clearly be put to much more useful scientific endeavors?"
Well, possibly to stimulate public curiosity to garner political support for more publicly funded projects?
In the US, PR stunts are very important to science in terms of getting budget $$. See "NASA" circa 1965-2005. And what a great way for US to garner more support for a Mars invas... um, landing.
Of course, it being a non-USian telescope, perhaps capturing images of the US flag on the moon is not the best way to get public funds for your projects...
"Trolls they were, but filled with the evil will of their master: a fell race..." -- J.R.R. Tolkien on Olog-hai