Telescope

Telescopes collect light largely for two types of analysis, imaging and spectrometry. The better known is imaging, the goal of which is simply to produce an accurate picture of the objects which are being examined. In past years, the only means of recording an image was to take a photograph. For long exposure times, the telescope had to track the sky by rotating at the same speed as Earth, but in the opposite direction. This is still the case today, but the modern telescope no longer uses photographic film but a charged coupled device (CCD) array. The CCD is a semiconductor light detector, which is fifty times more sensitive than photographic film, and is able to detect single photons. Being fabricated using semiconductor techniques, the CCD can be made to be very small, and an array typically has a spacing of 15 microns between CCD pixels. A typical array for imaging in telescopes will have a few million pixels. There are many advantages of using the CCD over photographic film or plates, including the lack of a developing stage and the output from the CCD can be read directly into a computer and the data analyzed and manipulated with relative ease.

The second type of analysis is spectrometry, which means that the researcher wants to know what wavelengths of light are being emitted by a particular object. The reason behind this is that different atoms and molecules emit different wavelengths of light; measuring the spectrum of light emitted by an object can yield information as to its constituents. When performing spectrometry, the output of the telescope is directed to a spectrometer, which is usually an instrument containing a diffraction grating for separating the wavelengths of light. The diffracted light at the output is commonly detected by a CCD array and the data read into a computer.