Telescope

Telescope

Light and other kinds of electromagnetic radiation coming from the universe outside the Earth must travel enormous distances through space and time to reach observers. Only the brightest and nearest stars can be seen with the unaided eye. To see farther and to clarify and measure what is seen, a telescope is needed. The word telescope is derived from the Greek words tele, "from afar," and skopos, "viewer." Even a simple homemade telescope can clearly show Saturn's rings, Jupiter's bands and red spot, stars, nebulae, and nearby galaxies not visible to the unaided eye. The ability to study the distant planets and other structures in the universe with these powerful yet remarkably simple instruments has revolutionized mankind's understanding of the natural world.

All telescopes gather radiation from distant objects over a large area and focus it, thereby increasing the intensity of the radiation and allowing the objects to be magnified. Sophisticated telescopes are used to view radiation in all parts of the electromagnetic spectrum from long-wave radiation and radio waves to infrared radiation and light and much shorter wave radiation, including ultraviolet and X rays.

This radiation travels through space at the speed of light in the form of waves of electric and magnetic fields. Because of its basic similarity, all such radiation can be focused by reflecting it off a curved surface or by refracting, or bending, it with glass lenses. The devices that are used to do this, however, vary, depending on the wavelength or type of radiation being studied.

Optical Telescopes

The first telescope developed, and the one most widely used, is the optical telescope, which gathers visible light radiation. There are three basic types of optical telescopes: refractors that use lenses, reflectors that use mirrors, and catadioptrics that use a combination of both lenses and mirrors.

The refracting telescope has a closed tube. At one end of the tube is the object glass, usually made of two or more lenses, that admits light emanating from the object observed. The light rays are refracted by the lenses to a point of focus at the lower end of the tube where the eyepiece is located.

The eyepiece acts as a magnifying glass and enlarges the bright image. An observer can view objects through the eyepiece or attach a camera to the telescope to record images.

The reflecting telescope focuses light rays with a large curved concave mirror that is generally made of glass covered with a thin coating of aluminum.