Astronomers use large telescopes and giant cameras and record images on photographic film. This is done because film is more sensitive than eye and can store light. In addition, the longer it exposed, the more light it stores, which enable it to record very faint stars and galaxies. Light coming through the telescope is also analysed, notably in spectroscopes that split it into spectrum. By studying the spectrum, astronomers can discover a remarkable amount of information like its composition, temperature and speed about the star the light came from.
CAMERAS ON TELESCOPES
Since the 19th century astronomical photography has been an important tool for astronomers. By attaching a camera to a telescope that has been specially adapted with motor that can be set to keep the telescope turning at the same speed as the rotation of the Earth, the astronomers can take very long exposures of distant stars. Before the invention of photography, astronomers had to draw everything they saw. They had to be artists as well as scientists.
(above) Stars trail in circular arcs around the north pole in this long-exposure photograph.
Recently, electronic methods of light detection which are over a hundred of times more sensitive than the best photographic film that have come into use. They include device as charged-couple devices (CCDs). They are kinds of silicon chips that are light sensitive. These chips are very thin layers of semiconductor material. They contain thousands of tiny photon detectors, the pixels. These are a quarter of a million of these to every square centimetre of chip. The photons of light trigger off each pixel when they hit it. When photons of light hit a pixel, it releases an electron, This charged particle then moves to form a current. The pattern of incoming light produces on the chip a pattern of charges, which a computer can convert into visible images.
(above) Shows a CCD screen.