A comet is an icy body that releases gas or dust. They are often compared to dirty snowballs, though recent research has led some scientists to call them snowy dirtballs. Comets contain dust, ice, carbon dioxide, ammonia, methane and more. Astronomers think comets are leftovers from the gas, dust, ice and rocks that initially formed the solar system about 4.6 billion years ago.
heir annals for 164 BC and 87 BC contain unmistakable references to a comet that can only be Halley’s putting in its regular appearances according to the schedule established by Yeomans and Kiang. It is a remarkable fact that observations made with the naked eye 2000 years ago, and impressed into clay tablets in cuneiform script, are still of value in this day of high-speed computers and space probes.