Comets have been instilling fear and awe into us since man first began to look toward the sky. As early as 240 B.C. the Chinese began to document the appearance of Halley’s Comet. Ancient Greeks believed that comets resembled stars with hair flowing behind them. It is from the Greek word for “long haired” that we get the word “comet”. In ancient times, before scientists discovered what exactly comets are, many people believed that comets were a curse or a harbinger of tragedy and misfortune. It was this belief that comets were a sign of a curse that led the Roman Emperor Nero to order all of his potential successors to be executed. More recently, in 1910, as the earth passed through Halley’s Comet’s tail, businessmen took advantage of people’s fears of impending doom and sold items such as gas masks, “anti-comet pills” and umbrellas to protect users from the dangers of the comet. This may seem a bit comical until we consider that one theory as to why the dinosaurs and seventy percent of all living species on earth suddenly died out about 65 million years ago involves a comet. The theory states that a comet approximately ten kilometers in size may have struck the earth, releasing large quantities of dust and rocks into the atmosphere and thereby significantly altering the environment. Fortunately for us, there is no scientific evidence to indicate that the earth will experience such an impact anytime in the foreseeable future.
What exactly are these beautiful yet feared celestial bodies? Comets are actually made up of rocky material, dust, gases and ice from the far reaches of the solar system that have been carried around for about 4.5 billion years. One scientific theory suggests that the carbon, water and other components of life on Earth were actually brought to the planet by a comet or its debris. It is believed that all comets come from one of two regions in space, the Oort Cloud and the Kuiper Belt. Comets orbit the sun just like the planets of our solar system do. When a comet is moving towards the sun, it travels head-first but when it’s moving away from the sun, it travels tail-first. Comets actually don’t have tails until they get near the sun. As a comet approaches the sun, the heat from the sun begins to the melt the comet’s nucleus and the resulting material, blown by the solar wind, streams behind the comet, forming its tail. It can take a comet as few as seven or as many as millions of years to complete an orbit. Because comets are so small relative to the universe, scientists have not yet seen any comets outside of our solar system. Meteor showers on Earth are actually caused by Earth passing through comets’ orbits. Debris left behind by the comet penetrates our atmosphere, raining down. It is believed that there are as many as two million comets in our solar system. Approximately five new comets are discovered every year and the total number of comets that have been identified so far is well over three thousand.