Coma. As a comet gets closer to the sun, the ice on the surface of the nucleus begins turning into gas, forming a cloud around the comet known as the coma. According to science website howstuffworks.com the coma is often 1,000 times larger than the nucleus. Outside the coma is a layer of hydrogen gas called a hydrogen halo which extends up to 1010 meters in diameter. The solar wind then blows these gases and dust particles away from the direction of the Sun causing two tails to form. These tails always point away from the Sun as the comet travels around it. One tail is called the ion tail and is made up of gases which have been broken apart into charged molecules and ions by the radiation from the Sun. Since the most common ion, CO+ scatters the blue light better than red light, to observers, this ion tail often appears blue.
Credit : lco global
Picture Credit : Google
