World's Largest Telescope Begins Production

JohnnyNapalm writes "The Aggie Daily News is reporting today that the first mirrors have been cast for the world's largest telescope. The result of cooperation from some of the foremost institutions in education and science in the nation, the Giant Magellan Telescope stands to operate at a resolution 10 times larger than the Hubble. The project, set to be constructed in Chile, is slated for completion in 2016."

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[spudchucker]

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Re:Largest Telescope?

[luna69]

For those of you not familiar with why astronomers would place (frickin') lasers onto telescopes, there are multiple reasons.

The primary reason is to provide a "fake star" that can be monitored for distortion, which helps adaptive optics systems counteract atmospheric distortion in the final telescope image/data. In other words, it helps remove the "twinkle" caused by the atmosphere.

The laser at Apache Point, as well as at other locations (see previous message), is used to measure the distance to the moon (which is useful in, among other things, studies looking at the accuracy of general relativity).

The Apache Point laser is capable of measuring the distance to the moon to a millimeter using this device. (think about it: at a telescope, up on a mountain around 10,000 feet, there's probably more 'flex' in the mountain itself!).

Report from the lab

[LMCBoy]

The Steward Observatory Mirror Lab had an open house yesterday for observatory personnel, which I attended.

The spin-cast oven is huge. In these pictures, you only see the top portion of it, it actually fills the floor below as well. I believe this is the only large spin-cast mirror facility in the world. The idea behind spin-casting is that, by spinning the molten glass as it is slowly cooled, you automatically get a paraboloid top surface. This makes the final shaping of the mirror much easier, since the first-order shape is already there.

Actually, in the case of the GMT, it will use seven mirrors, six of which are off-axis. The off-axis mirrors will obviously have a more complicated surface than a typical on-axis paraboloid. The mirror being cast now is an off-axis mirror; it is a proof-of-concept that they can grind an eight-meter chunk of glass to an off-axis paraboloid shape with a surface RMS of 20 nanometers (!).

In a few months when the mirror has cooled and solidified, it will be removed from the oven, cleaned, ground, and eventually, polished. The stress-lap polisher is very impressive. It has a network of stress actuators above it, which can dynamically change the shape of the polisher's surface as it travels across the mirror.

It's interesting that the "Aggie Daily News" was chosen as the linked story, which makes it sound like UT Austin and Texas A&M are the major players in the GMT, along with a handful of other, unnamed institutions. In fact, the Carnegie Institute is the impetus behind the project, and the U of Arizona is providing the mirrors. I think this UA News article is much more informative.