The DCT First Light Challenge |
The guider and wavefront sensor is one of the critical components of the DCT. |
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What's the Guider? 
High resolution astronomical imaging has always required tremendous tracking precision regardless of how perfectly the telescope and mount are constructed and aligned. In 1912, when V. M. Slipher began imaging faint "spiral nebulae" with the Clark telescope, he manually guided the telescope by focusing his eye on a "guide star" centered in a finder scope. Today, modern research telescopes like the DCT use an autoguider to ensure the telescope tracks the target object precisely. In an autoguider, a small fraction of light from the telescope's optical path is diverted to the autoguider camera. The autoguider takes continuous short exposures of a guide star, monitoring changes in its position and issuing commands to the telescope drive system that exactly counteract drifts in the star's position. In this way, the telescope stays pointed at exactly the same spot for exposures both short and long. This is not only more precise than the method Slipher had to use, but much less tedious! |
What's the Wavefront System? 
In the picture at left, you can see the DCT mirror in its polishing facility at the University of Arizona College of Optical Sciences lab. The mirror is upside down, and a technician is attaching mounting points for 120 actuators - small devices like pistons that can push against the surface of the mirror. As the telescope moves, the shape of the very thin mirror (it's 14 feet across but only four inches thick) will change slightly. "Slightly," however, is enough to degrade the images. Here's where the wavefront sensor comes in. It is a complex system of detectors and software that measures the image quality at different points all over the mirror. If the system detects that the image in certain parts of the mirror has degraded, it will send signals to the necessary actuators to deform the mirror at those points, in precisely the manner needed to recover the optimum shape. This engineering and software wizardry will continuously "massage" the mirror, subtly deforming it to make sure the DCT gives the best possible image - every minute of every night. |
GWAVES is very complex and very specialized; taken together, those qualities mean very expensive. But the DCT depends on every single link in the chain, and GWAVES is one of them. Your tax-deductible gift will help make GWAVES a reality.