The Great Comet of 1997 grabbed headlines when it lit up the night sky.
Often cited as the most observed comet of all time, Hale-Bopp was visible in the night sky for 18 months during its flyby of Earth in 1997. It was the first comet to be discovered by a small amateur telescope. Hale-Bopp is roughly 40 kilometres (25 miles) in diameter. It is mainly because of its large size that it appears so bright. Its solid centre – the nucleus – is a frozen and dusty wasteland mostly composed of ice that reflects a large amount of sunlight. The nucleus is surrounded by a combination of gases and dust – known as the coma – such as a metal-rich silicate mineral.
The light coming out of the comet is a product of ice evaporating and disintegrating into a cloud of particles. Hale-Bopp provided an abundance of information on the physical and chemical nature of comets, including the presence of a third tail made of sodium trailing the comet in addition to a dust and gas tail.