Telescope
The word “Telescope”
The word "telescope" was coined in 1611 by the Greek mathematician Giovanni Demisiani. It is composed of two words, “tele” and “scope”. These words come from Greek language, tele=far and scope=seeing. Therefore “Tele-scope”=”Far-seeing”.
Introduction:
A telescope is an optical instrument used for viewing distant objects. Telescopes are of two types, namely reflecting telescope and astronomical telescope. Telescopes are used for many purposes. Telescopes are used to study and discover planets, galaxies and other undiscovered facts about space. In early times telescope were used to spot enemies and battle ships in the ocean. In today world telescopes are very advanced.
Telescopes: |
Optical Telescopes : Astronomical telescope(Refracting telescope) and reflecting telescope
Optical telescopes:
Refracting telescopes(Astronomical telescope): an astronomical telescope is used to view celestial bodies. The main parts of an astronomical telescope are, objective lens, eyepiece and telescope tube. Objective lens is a convex lens with large focal length and large aperture. The eye piece is a convex lens with a short focal length. Telescope tube has a set of two mounted brass tubes where one tube can easily be slide in other. The objective lens and the eyepiece are fixed at the ends of the telescope tube. The distance between the objective lens and eyepiece can be adjusted.
How it works
The rays of object are parallel to each other. This parallel beam of light is focused by an objective in the focal plain and is perpendicular to its axis. This image is refracted be the eyepiece and the final image is formed at infinity.
History
The first idea of telescope was invented by Hans Lippershey from Holland. He discovered that an object can be magnified using two piece of lens when place at an appropriate distance from each other. In 1609 the great Italian scientist named Galileo Galilei was the first one to capture the images of moon and to prove that the surface of the moon was not smooth, actually It had a lot of cavaties and craters. He also discovered the sunspots on the sun, the four large moons of Jupiter and the rings around Saturn. Galileo’s telescope only magnified 30 times.
Reflecting telescope: reflecting telescope is also known as newtonion type telescope because it was first designed by Sir Isaac Newton. In reflecting telescopes concave mirror is used to form secondary image which is then refracted by the eyepiece (convex lens). Reflecting telescopes are used to view objects such as planets, moon, star clusters and galaxies.
How it works
In reflecting telescopes includes telescope tube, a parabolic concave mirror, a plane mirror and an eyepiece. The parallel beams coming from the object is reflected on the parabolic concave mirror. These rays after reflecting fall on a plane mirror and then the rays are reflected in the eyepiece which is placed in an opening in the telescope tube. This is how reflecting telescopes work.
History
In 1704 Sir Issac Newton made a new concept of telescopes. He invented reflecting telescope that used a concave mirror that gathered the rays at one point (focal point). The reflecting mirror gathered more amount of light which made the image more clearier. His idea of using concave mirror instead of concave lens opened the door to magnifying object millions of times; far beyond what could ever obtained with a lens.
Five most powerful optical telescopes:
1). Keck Observatory, began science operations in 1993, Hawai
2). Hubble Space Telescope, launched in 1990
3). Spitzer Space Telescope, launched in 2003
4). Large Binocular Telescope, first light in October 2005
5). Fermi Gamma-Ray Space Telescope, launched in 2008
Radio telescopes:
Radio telescopes collect radio waves from distant space bodies and focus them on to a detector. With the help of these instruments we began to build a completely different view of the Universe. Radio telescopes are used to study naturally occurring radio emission from stars, galaxies, quasars, and other astronomical objects between wavelengths of about 10 and 1 millimeter. At wavelengths longer than about 20 centimeters, the atmosphere disturbes the incoming signals. This causes a phenomenon known as scintillation
How it works
Radio telescopes have two basic components: (1) a large radio antenna and (2) a sensitive radio receiver. The sensitivity of a radio telescope--i.e., the ability to measure weak sources of radio emission--depends on the area and efficiency of the antenna and the sensitivity of the radio receiver used to amplify and detect the signals.
Usage of telescopes in today’s world
These powerful telescopes are used by various space agencies around the world (example NASA, Canadian Space Agency). NASA uses these telescopes to discover outer space. NASA has sent these telescopes in space to get better images of stars, planets, galaxies and much more. These telescopes are up in the space orbiting the earth taking images which have helped us to gather information about space. These powerful telescopes take images of distant objects. An example of such telescopes which are up in the scape is Hubble telescope.
Difference between optical and radio telescopes :
Think of your eyes as a pair of small telescopes. You can see very well during the day but it is very difficult to see at night because our eyes only work well when there is enough light. The same is true for optical telescopes. They require sufficient light from the star in order to display the star’s image. Bigger lenses help gather more light in bigger telescopes, this is why telescopes have grown in size since they were made.
Now think of your ears that gathers more information about your surrounding environment than the eyes do in the light or in the dark. In the 1930’s an engineer named Karl Jansky discovered that the sun imitates radio waves. He and his partners developed a device that can gather radio waves from distant celestial bodies known as radio telescope.