The image sensor in a CCD camera is the CCD chip. 2048 x 2048 pixels. The pixels themselves range in size from 9 microns to 30 microns. CCD, by the way, stands for charge coupled device.
Light striking each of the pixels on the CCD chip is converted to electric charge.
This charge is greater where there is more light and less where there is less light. At the end of each exposure, the charge on each pixel is read by the computer and the picture is formed. During this exposure the telescope must track the stars VERY precisely. In fact, the most important part of CCD imaging is a good telescope drive. I have used five different cameras, made by either Santa Barbara Instruments or Finger Lakes Instruments .