Astronomers haven't looked through telescopes with their naked eyes since the early part of the twentieth century. Up until the 1980s photographic plates were used to capture light. These glass plates were coated with an emulsion that is very sensitive to light; the emulsion is similar to, but much more sensitive than, the coating on film in a camera. However, this emulsion is not very efficient -less than 1 percent of the light falling on it makes the chemical changes that we see as a picture. Now, astronomers use chargecoupled devices (CCDs), just like modern video and digital cameras. These CCDs can be very efficient; over 90 percent of the incoming light is captured for use. A 1-meter telescope with a CCD camera can see objects fainter than a 4-meter telescope using photographic plates. Moreover, the information gathered by CCDs is already in digital form, so it can be easily manipulated by computer.
Was this article helpful?