Our knowledge of comets is based on what we see as they travel nearest the Sun in their orbits around the star.
Except for comets with relatively short orbits, we don’t know how far or precisely where else they travel.
As a comet nears the Sun, the ice in the nucleus begins to melt, creating a huge gaseous cloud called the coma.
The nucleus and the coma together are called the head.
At the same time, the solar wind blows particles of comet dust and gas into separate tails. The tail of gas can extend hundreds of millions of miles (km), while the dust tail is generally shorter.
While comets have two tails, they are commonly perceived as one by non-astronomers, and are often referred to in the singular “tail,” rather than “tails.”
As a comet nears the Sun in its orbit, its rock-and-ice nucleus decomposes, sometimes completely.
Solar wind blows dust and gases away from the comet’s head in two tails.
There are two tails because the densities of dust and gases react differently to the force of the solar wind.