What is CCD Astronomy?

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  2. March 24, 2014 1:55 am

What is CCD Astronomy?

CCDs or Charge-Coupled Devices have been around since 1969 and have been used in a number of different ways. They are made of silicone, just like the chips in a computer. But in the case of a CCD, electronic circuitry is attached to the silicone to take advantage of the fact that silicone releases electrons when exposed to light. CCDs are made up of pixels which are lined up in columns and rows. When exposed to light, each pixel collects an electric charge and holds it. That is how it stores images.

The application of CCDs in the field of astronomy was due in large part to the fact that their quantum efficiencies are extremely high, and also to the linearity of their outputs. Of course their ease of use when you compare them to the bulky photographic plates in use at the time was also a contributing factor.

In CCD Astronomy, light gathered from a telescope is focused onto a CCD or a bank of them, instead of a photographic plate. Things like thermal “noise” and cosmic rays can alter pixels, so astronomers compensate for that by taking exposures with the shutter opened and closed, then averaging the image. Digitized images are then downloaded.

Taking advantage of some useful properties of CCDs, astronomers do something called drift-scanning. This can actually make a fixed telescope perform like a tracking telescope. Digital images from the CCDs are transferred in a direction parallel to the apparent motion of the sky and also at the same speed. This allows the telescope to deliver an image of the sky that is significantly larger that its normal field of view. CCDs, these magnificent pieces of silicone are hard at work in other fields of science as well and we will be hearing from them.

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