Telescope is a kind of optical instrument, which can magnify the distant objects by using the arrangement of lens or curved mirror and lens, or by transmitting, absorbing or reflecting electromagnetic radiation to observe the distant objects. The first known practical telescope was the refraction telescope invented in the Netherlands in the early 17th century by using glass lenses. They found it useful in both ground applications and astronomy.

The reflecting telescope, which uses mirrors to collect and focus light, was invented within decades of the first refracting telescope. In the 20th century, many new telescopes were invented, including radio telescopes in the 1930s and infrared telescopes in the 1960s. The term telescope now refers to various instruments that can detect different areas of the electromagnetic spectrum, and in some cases other types of detectors.

Optical telescopes mainly collect and focus light from the visible part of the electromagnetic spectrum (although there are some works in infrared and ultraviolet). Optical telescopes increase the apparent angle and brightness of distant objects. In order to observe, photograph, study images and send them to a computer, telescopes work by collecting light and other electromagnetic radiation using one or more curved optical elements, usually made of glass lenses and / or mirrors, so that telescopes work. Light or radiation to focus. Optical telescopes are used in astronomy and many non astronomical instruments, including theodolites (including transit), sight glasses, monocles, binoculars, camera heads and telescopes

Radio telescope is a directional radio antenna used in radio astronomy. Dishes sometimes consist of a conductive mesh with an opening smaller than the wavelength observed. A multi-element radio telescope is composed of these dish antennas in pairs or groups to synthesize large "virtual" apertures, which are similar in size to the spacing between telescopes. This process is called aperture synthesis. As of 2005, the current recording array is many times the width of the earth - using space-based very long baseline interferometry (VLBI) telescopes, such as Japan's halca (advanced laboratory of communications and Astronomy) VSOP (VLBI Space Observatory program)) satellite. At present, aperture synthesis is also using optical interferometer (optical telescope array) and aperture mask interferometer of single reflection telescope for optical telescope. Radio telescopes are also used to collect microwave radiation, when any visible light is blocked or weakened (such as signals from quasars), and microwave telescopes are used to collect radiation. Programs such as SETI and Arecibo use some radio telescopes to search for extraterrestrial life.

High energy X-ray and gamma ray telescopes cannot focus completely, but should use a coded aperture mask: the shadow pattern produced by the mask can be reconstructed to form an image.

X-ray and gamma ray telescopes are usually located on satellites orbiting the earth or balloons flying high above, because the earth's atmosphere is opaque to this part of the electromagnetic spectrum. However, high-energy X-rays and gamma rays cannot form images in the same way as visible telescopes. The Fermi gamma ray space telescope is an example of such a telescope.

Compared with conventional gamma rays, the detection of very high energy gamma rays with shorter wavelength and higher frequency needs further specialization. An example of such an observatory is veritas. Like visible light, very high-energy gamma rays are still photons, while cosmic rays include particles such as electrons, protons and heavier nuclei.

The telescope bracket is the mechanical structure supporting the telescope. The telescope bracket is designed to support the weight of the telescope and can accurately align the instrument. Over the years, a variety of mounts have been developed, most of which focus on systems that can track the movement of stars as the earth rotates.