My Science School

            Galileo (1564-1642), the great Italian scientist and mathematician, was the first astronomer to use a telescope, the discoverer of the pendulum’s laws and the founder of modern physics.

            Two of his great contributions to knowledge are associated with famous buildings in Pisa, the northern Italian city where he was born. When Galileo was 19, he observed a lamp swinging in the cathedral. From its movement he concluded that a pendulum swinging to and fro could be used for measuring time, and so prepared the way for the invention of the modern clock. By dropping objects from the Learning Tower of Pisa he demonstrated that bodies of different weights fall at the same rate.

            While Professor of Mathematics at the University of Padua (1592-1610), Galileo made his first telescope by fitting a lens at each end of an organ pipe. Later he made a telescope that magnified 30 times. He found that the Milky Way was a mass of stars, studied the moon and discovered the four largest satellites of the planet Jupiter.

            Galileo’s observations convinced him that Nicholaus Copernicus (1473-1543), the Polish astronomer, was right in his theory that the earth rotates on its axis and revolves round the sun. This view was contrary to the teaching of the Church, and in 1616 he was given o formal warning. But in 1632 he published a dialogue in support of the Copernican system that offended the Church by its satire and use of Holy Scripture. He was summoned before the Inquisition, forced to retract his views and made to live in seclusion for the rest of his life.

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The first dish (or radio) telescope was made in 1942 by an American Grote Reber, of Wheaton, Illinois. He constructed his apparatus after studying the experiments of K.G. Jansky, another American. Jansky discovered in 1935 that the intensity of radio waves increases as a highly sensitive aerial is directed progressively nearer to the Milky Way. The maximum intensity is reached when the antenna is pointing towards Sagittarius that is to say, towards the galactic centre.

      Radio telescopes are called dish telescopes because of the steerable dish-shaped or parabolic reflector which gathers the radiation and focuses it on to a centrally mounted aerial. The surface of the dish is made of a good electrical conductor and the radio waves are reflected from it. The parabaloid shape ensures that all the reflected rays arrive at the central point, where they are “swallowed” by an electromagnetic horn and fed into a receiver.

    Since the Second World War the development of radio telescopes has gone ahead rapidly. A 250-foot diameter instrument was installed at the Nuffield Radio Astronomy Laboratories at Jodrell bank, Cheshire, England. It is under the direction of professor under the direction of Professor Sir Bernard Lovell and has already contributed a great deal of new information to astronomy.

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            The sextant was invented in England in 1732 by John Hadley. Hadley’s instrument is used mainly at sea to determine a ship’s latitude, or distance from the equator. Its invention laid the foundation of modern navigation with the aid of the sun and stars.

              The instrument is so called because it is equipped with an arc which is usually one-sixth of a circle, or 600. It measures the angle of the sun’s or a star’s altitude above the horizon. As this angle varies with the distance from the equator, the information obtained helps the navigator to calculate his position. All he needs in addition is the time, the date and the longitude which can be found by comparing local time with the time at Greenwich.

         To operate the sextant, the navigator looks through its small telescope straight at the horizon. At the same time, an image of the sun is reflected by mirrors into the user’s field of vision. When the sun is made to appear exactly on the horizon, the arm which moves the mirrors gives the required measurements to calculate the ship’s position.

       The handling of a sextant is generally to as “shooting the sun”.

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