SDSS Instruments: Recording Information
For most small telescopes, your eye is the detector, but if your goal is to have survey information available for many scientists to use, then you need to record that information. In the case of the SDSS telescope, the two instruments that can be attached to the telescope to record the light are the CCD camera and the spectrographs. They record light in different ways.
The CCD Camera
Digital cameras are designed to record images. The recording surface of the camera is called a charged coupled device, or CCD. The CCD is a grid of tiny “light buckets” called pixels. The energy from the light striking the surface kicks off electrons which are then amplified, collected, and counted. The amount of charge produced by the light striking each pixel is recorded as a grid of numbers. When these numbers are read off in order, a computer can reconstruct digital images of the captured light.
The job of any telescope is to collect and focus light. If you’re looking for a good analogy, try thinking of a telescope as a light funnel. A funnel collects liquid over a large area and focuses it through a much smaller opening. A great tool, of course, but you can imagine that a funnel wouldn’t be much good if you didn’t capture the liquid coming out at the other end. What a useless mess! The same thing is true for a telescope; we have to capture all of the light being gathered, focused, and directed through the back of the telescope.