Comets

If you happen to gaze up in the sky at just the right time in the year 2061, you might get to see one of the most famous comets of all. It’s called Halley’s Comet, and people get a chance to see it every 76 years when the comet’s orbit brings its close to Earth.

Comets are satellites made up primarily of ice (both water and frozen gases) and dust. All comets orbit the Sun, but seme complete a revolution of the Sun in just a few years while others need several hundred thousand years. When a comet passes close to the Sun, the ice in the comet melts and dust particle are released. These dust particles from the comet’s famous tail, or “long hair,” which can extend for more than 10 million kilometers. It should be no surprise that the word comet comes from the Greek word kometes, which means “long-haired.”

For much of human history, people were terrified of comets. These bizarre objects seemed to appear suddenly out of nowhere, and unlike the Sun and stars, they seemed to have no predictable pattern. Some people thought comets were messengers, bringing news of disasters to come. Comets were blamed for earthquakes, wars, floods, and assortment of other catastrophes. It wasn’t until late in the 17^th century that Sir Isaac Newton discovered that comets orbit the Sun in predictable patterns, a discovery that helped to dispel many people’s fear of the long-haired messengers of doom.

Edmond Halley, another famous astronomer, was born in London, England, in 1656. He studied astronomy at Oxford University until 1676, when he went off to study the stars and planets of the southern hemisphere. Later, he compiled his data in a book about the location of the stars in the sky; he was the first person to map them accurately. Halley also observed the Moon and studied how it affects the ocean tides. He helped to find a way to measure distances in space. This measurement system was used by other scientists to learn about the size of our solar system and the distances of many stars and planets from Earth.

Edmond Halley was especially fond of studying comets. He read about comets and observed them in the sky. He learned about the way they move around the Sun, each comets following a different path and travelling at its own speed. Over time, he calculated the orbits of 24 comets that he had either read about or seen himself.

Halley noticed that the paths of a comet seen in 1531 and of a comet seen in 1607 were identical to the path of a comet he had observed in 1682. He concluded that these three comets were, in fact, the same comet. Because Halley accurately predicted that the comet would come again in 1758, it was decided to name the comet after him. The earliest known reports of Halley’s Comet were actually made over 2,000 years ago by Chinese astronomers, so we know that it has been orbiting the Sun for more than 2,000 years. Halley’s comet is one of the brightest comets—bright enough for people to see without a telescope.

The orbits of more than 850 comets have now been calculated. Of these, at least 184 are called periodic comets because they orbit the Sun in less than 200 years. Studying comets may give us information about  the origins and formation of the solar system. In 2004, the Stardust spacecraft flew within 236 kilometers of a comet called Wild 2. From this distance, the Stardust was able to take extraordinarily detailed photographs of the comet. Then, in a 12-minute pass trough Wild 2’s dust and gas cloud, the Stardust mission was able to collect a spoonful of comet dust to bring back to Earth for further study. Another spacecraft called Rosetta is expected to actually land on a comet named Churyumov-Gerasimenko in the year 2014.

With satellite providing more and more information, comets will continue to captivate professional and amateur astronomers, as well as the general public. And if we are fortunate, comets may soon answer some fundamental questions about the origins of the solar system.

Source : Kosayu’s XII Student Handbook