Telescope
From ArticleWorld
To observe distant objects special instruments called telescopes are used because human eyes are ill-equipped to view objects beyond certain distances.
In 1611 Galileo Galilei gave the telescope its name after modifying an instrument made by a spectacle-maker, Hans Lippershey who bears the original credit together with Zacharias Janssen (another spectacle-maker) and Jacob Metius.
The word telescope is derived from two Greek words ‘tele’ and ‘skopein’ meaning far and to see respectively. Basically the telescopes are designed to collect electromagnetic radiation (i.e. light) which is then subjected to further analysis and study.
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Types of telescopes
Various telescopes operate in almost the entire region of the electromagnetic spectrum though they are referred usually to the optical region (visible, ultraviolet and infrared). And hence the different types:
- Optical telescopes
- Radio telescopes
- X-ray and gamma-ray telescopes
Optical telescopes
These are most common and popularly used in astronomy. They employ optical elements like lenses or mirrors which collect and focus light (mainly from the visible region). This enables one to observe an image with a greater apparent angular size and brightness.
The three main types include refracting, reflecting and catadioptric telescopes that make use of lenses, mirrors and their combination respectively. Optical telescopes also find application in camera lenses, binoculars, theodolites, spyglasses etc.
Radio telescopes
A radio telescope is simply a directional radio antenna parabolic in shape (dish) which helps detect radio sources for further study. They are also configured to be used in pairs or in groups. They are then called multi-element radio telescopes where the signals from the telescope group are collected and mixed to produce a high-quality image. This technique is called aperture synthesis and is presently adopted with optical telescopes too.
The year 2005 saw a record in the array size which is many times earth’s diameter. This array had in it special telescopes by name Very Long Baseline Interferometry (VLBI) telescopes such as the Japanese HALCA ((Highly Advanced Laboratory for Communications and Astronomy) VSOP (VLBI Space Observatory Program) satellite.
X-ray and gamma ray telescopes
X-rays and gamma-rays penetrate through most of the metals and glasses. This is a hurdle when it comes to receiving these signals. So some X-ray telescopes use ring-shaped glancing mirrors made of heavy metals that reflect the rays to only a few degrees. The gamma-ray telescopes use coded aperture masks which create shadow patterns that can be reconstructed to form an image. These telescopes detect satellites of the earth and high flying balloons.
Besides there are other telescopes like solar telescopes, spotting scopes etc. Some renowned telescopes are Hubble Space Telescope, Very Large Array and Isaac Newton Telescope.