My Science School

Clyde Tombaugh, a young American research student, made the last discovery of a planet while working in 1930 at the Lowell Observatory, Arizona state College. This planet is Pluto, the ninth one in order of distance from the sun, 3,670 million miles away.

    Although Tombaugh, who was 26 at the time, was the first astronomer to see Pluto, its existence had been suspected by Percival Lowell, builder of the observatory at Flagstaff, Arizona. Lowell began searching for the planet in 1905, the year before Tombaugh was born. He observed that there was a difference between the predicted and actual positions of Uranus, and this led him to conclude that there must be another planet. His final calculations about “panel X” were published in 1914, but he had still not found the planet when he died two years later.

    Another American, W.H Pickering, took up the search, concentrating on the irregular movements of the planet Neptune. He saw a clue in the movement of comets, which seem to be attracted by large planets. Here were 16 known comets whose paths took them millions of miles beyond Neptune. Which is 2,800 million miles from the sun, and Pickering was convinced that they were being attracted by a still more distant planet.

   In 1919 yet another hunt was begun by Milton Humason at Mount Wilson Observatory, Pasadena, California. Instead of mathematical calculation, Humason tried photograph. He took two pictures of a series of stretches of the sky, with a gap of one or two days between exposures. In such photographs stars stay still, but planets change position.

    When Tombaugh discovered Pluto, it became clear that Humason had photographed the planet twice. Once it had been masked by a star, and the second time its image had coincided with a flaw in the photographic plate. The main difficulty in the search had been that Pluto was extraordinarily faint. Pickering formed the opinion that it was not Lowell’s planet X, but that a huge planet remains to be discovered.

Picture credit: google

A star is a body of luminous gas, like the sun. But as stars are much farther away from the earth than the sun, they appear to be only small points of twinkling light. With the naked eye it is possible to see about 2,000 stars at any one time or place but with the most powerful telescope over 1,000 million stars are visible. Although light travels at 186,000 miles a second, the light from the stars takes many years to reach the earth.

     Stars are not fixed in space, but are travelling in different directions at different speeds.  Seen from the earth, these movements appear to be so small that groups of stars, or constellations, seem to have a permanent relationship. The star patterns we see in the sky are almost the same as those seen by our ancestors hundreds, or even thousands of years ago.

    The sizes of stars vary tremendously, from less than the diameter of the sun to thousands of times its size. Most stars appear white when looked at with the naked eye, but some are bluish-white, yellow, orange and red. The varied colours are due to differences in surface temperature. The brilliant, white stars are the hottest with surface temperatures of several hundred thousand degrees. The less brilliant, orange and res stars have surface temperatures of about 2,000 degrees.

      There are exceptions, however. Te red giant, betelgeux, in the constellation (or group) of Orion, appears to be brilliant because of its size. Its diameter is 250 million miles, which is greater than the diameter of the earth’s orbit round the sun.

     Shooting stars which are sometimes seen moving across the night sky for a few seconds are really meteors. These small particles flare up as they strike the earth’s atmosphere and usually burn out.

Picture credit: google

In the beginning our universe was a mass of white-hot vapours and molten materials whirling about in space. Our world was formed from this. Astronomers believe it took millions of years for the cloud to cool, contract and begin to turn into molten rock.

      Modern astronomers think that many millions of years ago there was a huge explosion in space. They do not know exactly what happened. But it is possible that our sun exploded or that a much bigger companion star of the sun became a supernova-that is, it broke up violently. The debris and blazing gases from this explosion were, it is thought, flung far into space.

      For more millions of years our solar system boiled and bubbled. But very slowly, the fiery redness began to cool and condense into the nine planets and many smaller bodies. All these planets now revolve around the sun.

     After further vast periods of time the lava of the earth began to solidify, developing over many millions of years, into the world as we know it today.

Picture credit: google