Although simple telescopes can be used to discover fascinating objects in the sky, there have been other options available for a long time to get more detailed information on the heavenly bodies and their environment.
During the 16th and 17th century, developments in optical astronomy resulted initially in refractors (lens telescopes) and reflecting telescopes. Refractors consist of a collecting lens (the objective) that collects the rays of light.
These generate, at the focal point, an enlarged image that can be viewed through an ocular lens. The visual image is, however, inverted, but this is not a problem for astronomical observations. Even the telescope developed by Galileo Galilei provided a magnification of 30x. However, radiations of different wavelengths could not be bundled onto one focal point and the image was distorted.
Isaac Newton built the first reflecting telescopes. No collector lens is used in it; the light is trapped and collected by a hollow mirror. The mirror reflects the light equally for all wavelengths and at the focal point, generates a uniform image of the object.
We make a distinction between various reflecting telescopes such as the Newton or Cassegrain telescope, which work with different mirrors. Apart from optical telescopes, there are radio_telescopes that can measure radio_waves from space. They can be compared with the aerials of our radios. Normal radio telescopes look like large bowls.
They have a diameter between 50 and 100 meters, because the spectrum of radio waves is very large (1mm to 1 kilometer). The incoming signals have to be unified at one point. Then, they are amplified and processed in a computer. The largest radio telescope is located in Puerto Rico near Arecibo. It has a diameter of 305 meters and, in contrast to others, cannot be freely rotated.
