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>It is not possible to see periodic comets all of the time. Comets are very small and very faint objects in the night sky, too small to be seen when they are a long way from the Sun without their cloud of vaporised gases and dust. As a comet moves closer to the Sun it starts to melt and vaporise due to the Sun's heat, creating a cloud of dust and gas that shines in the Sunlight. The trails left by the comet give it its distinctive look.
The image above taken by the European Southern Observitory shows the comet Hale-Bopp at a distance of around half way between Saturn and Uranus note at this distance from the Sun the comet does not look as most people would expect.