Historically, comets have been observed with reverence and fear as ancient onlookers were unsure of what they were looking at. These guests in the night would sometimes glow eerie colors, and hang in the sky for days.
Of course, we now understand these objects to be dirty snowballs, glowing from the Sun's radiation and heat. Left over from the formation of the solar system billions of years ago, these beautiful objects occasionally find their way into the inner part of the solar system. But where do comets come from?
Short Period Comets
Generally, comets are broken up into two categories based on their origin. Short period comets, with long period comets being the other, come from a region of the solar system known as the Kuiper belt.
Out there, despite the large number of objects, there is a lot of empty space, lessening the possibility for random collisions or other interactions. But occasionally something occurs that will send a comet hurtling toward the Sun.
When this happens, the comet will find itself on a journey that will slingshot it around the Sun and back out to the Kuiper belt, a path on which it will continue until the Sun's immense heat erodes it away after repeated passes over time.
Each orbit will take the comet 200 years of less - defining the upper-limit for short period comets. This is why some comets, like haley's comet are so familiar because they approach Earth frequently enough that their journey is well understood.
Long Period Comets
On the other end of the scale, long period comets can have orbital periods of thousands of years or more.
These comets come from a much more distant region of the solar system - the Oort cloud. This theoretical sphere of comets and other icy bodies is thought to extend nearly a light-year away from the Sun; reaching nearly a quarter of the way to our Sun's nearest neighbor: Proxima Centauri.
Studying comets from this region is difficult because most of the time they are so distant that we can rarely see them from Earth, even with the most powerful telescopes. And when they do venture into the solar system's inner sanctum, they disappear back into the Oort cloud; gone from view for thousands of years.