Every few years a great comet, bright enough to be seen without a telescope, appears in the sky. Comets are a part of the solar system.
One of the most famous comets was observed in 1682 by Edmund Halley, a British astronomer. It was later named for him. Halley calculated the comet’s orbit. He was able to predict that it would return on an average of every 76 years, and it has done so, last being seen in 1986. The period of time varies slightly because of the pull of the planets.
Some scientists think that a comet is a frozen ball of ice and dust, perhaps 5 to 10 kilometers (3 to 6 miles) in diameter. When the comet is far from the sun, the ice remains frozen. But the comet does come nearer to the sun, at least for a short time. Then the sun’s light and heat cause the ice to evaporate (form gases). These gases are the glowing head, or coma, of the comet, which may appear as bright as the brightest stars. The solar wind (electrically charged particles from the sun) blows back some of the gas to form the comet’s tail, which may be over 100,000,000 kilometers (60,000,000 miles) in length.
Tags: British astronomer, Comets, Edmund Halley, Planets, Solar system, Sun, Telescope
