TELESCOPES
A telescope is an instrument that makes distant objects appears closer, allowing the viewer to see details that are not visible with the naked eye. Terrestrial telescopes are used for spotting wildlife (binoculars are made up of two telescopes, one for each eye), on gun sights and in periscopes. Astronomical telescopes are used to study objects in space. Terrestrial telescopes and most astronomical telescopes are optical telescopes, which collect light coming from distant objects and use it to produce images of the objects.
Italian scientist Galileo used the first astronomical telescope in 1609, with which he discovered moons around Jupiter.
There are two main types of optical telescope – refracting telescopes and reflecting telescopes. In a refracting telescope, a convex (bulging) lens collects light from the distant object and focuses it to form an image of the object. This image is very small, but is much larger than the image formed in the human eye. In a reflecting telescope, a concave (dish-shaped) mirror collects the light from the object and focuses it to form the image. Larger telescopes are nearly always reflecting telescopes because large mirrors are easier to manufacture than large lenses.
The Keck telescope in Hawaii has a main mirror 10 metres across. It is housed in a special building called an observatory.
The larger the lens of a refracting telescope or the mirror of a reflecting telescope, the brighter the image of the object observed, and the fainter the objects that can be seen with the telescope. The image is viewed with an eyepiece lens, which works like a magnifying glass to make it appear much larger.
RADIO TELESCOPES
Objects in space, such as stars and galaxies, do not just give off light. They also give off radiation from other parts of the electromagnetic spectrum, such as infrared radiation, radio waves, X-rays and ultraviolet radiation. These can show up objects that are otherwise invisible. They cannot be seen with ordinary optical telescopes, so special telescopes are needed.
Radio telescopes have a huge dish that acts as a reflector, collecting radio waves and focusing them on to a detector. Radio astronomy has allowed the discovery of new celestial objects, such as pulsars.
SPACE TELESCOPES
The Earth’s atmosphere stops many types of radiation from reaching the surface. To study these sorts of radiation, space telescopes must be launched into Earth orbit. They need special mirrors to reflect and focus the radiation, and electronic detectors to record the images formed, which are radioed back to Earth. Optical telescopes also benefit from being in orbit because the atmosphere distorts light rays as they pass through it. The Hubble Space Telescope, launched by space shuttle in 1990, is the most complex space telescope so far. It can detect visible light, infrared and ultraviolet rays.
The Hubble Space Telescope can see 10 times more detail than Earth-based telescopes and objects 50 times as faint. Solar panels provide its power. Images are transmitted via antennae.
Picture Credit : Google