From a scientific point of view, Comet McNaught, also called C/2006P1, was a chance to study the way our universe works. Discovered in August of 2006 by Scottish-Australian astronomer Robert McNaught, who has found 40 comets (so far), alone or in collaboration, it became the brightest comet the world had seen in forty years. Sadly for some, it was visible mostly in the Southern Hemisphere. On January 12th, at its nearest approach to the sun, it was plainly visible in daylight. At perigee on January 15th 2007, its nearest approach to the earth, it came within 0.82 AU of us, which is about seventy-six and a quarter million miles. A near miss, as the universe goes.
The study of Comet McNaught created new questions for astrophysicists with its powerful and unexpected effect on the solar wind, the stream of ions the sun shoots forth as it radiates light. Much about long period comets remains to be learned, though we know now about their elliptical orbits. Lumpy bits of water ice, dust, rocks and frozen gas, they stream in from the outer darkness to grow a misty coma as their dust reflects the growing sun and their frozen gasses ionize and stretch behind in the solar wind to tail away from the sun. Faster and faster they speed as they approach until they whip around the sun and chase their fading tail back out into the dark. In reality, a comet will have two tails, one of dust and rock, and one of ionized gas, but they may appear blended together. Often (by astronomical standards) comets will die in their orbits, overwhelmed by the sun, combust, or destroyed in collision with a planet or planetoid. Collisions throw some comets out of the solar system. Other comets may fade over the centuries until they are only a trail of dust, or until they are almost indistinguishable from a cold asteroid. Non-periodic comets, like Mcnaught, may never be seen from earth again, or not for more than 200 years.
Astrologers believe Great Comets, comets visible to the naked eye, portend great things. They may herald the death of a king, or the death of a civilization. They may foretell a momentous birth. Halley's Comet appears on the Bayeux Tapestry, which documents the Norman conquest of England. The Bible says a star appeared to the three Magi, to foretell the birth of Christ.
Maybe because they seem to disrupt the order of the heavens, they may cause panic when they appear. In 1910, for example, many people believed they would be killed by cyanogen gas as the earth passed through the tail of Halley's Comet. In the middle ages, comets were believed to bring plague.
To an ordinary person, a Great Comet is a visitor of terrifying beauty. It creeps out of the vast darkness, only visible to scientists craning over their instruments, and grows, and grows, burning away its substance to light its path. It swells to where we watch in awe. As it swings around the blinding sun it slows, to sweep a misty brilliant arc across the sharp-spangled field of infinite night. Then it is gone again.