Comets.......

Apologia Physical Science.

Comets, what are they?  This, of course, has no easy answers so I am just going to highlight some of the most interesting facts about comets.

~Did you know that there are an estimated hundreds of million comets?  Approximately 4,000 comets have already been discovered by scientist.

~Did you know that all comets, no matter what shape or size, all orbit the sun?

~The short-period comets are from the Kuiper belt and take just under 200 years to make a full orbit.

~The long-period comets, ISON for example, come from the Oort cloud which is near the edge of our solar system.  It is estimated that these comets take millions of years to complete an orbit.
~Comets often hit our planet.

~Did you know that a comet looks like a dirty snowball?  The reason is that the nucleus of a comet is made up of rock, dust, and ice.

~Did you know that a comet has its own atmosphere?  There is a fuzzy cloud which surrounds the comet's nucleus.  This fuzzy cloud is called a coma.

~It has always been thought that a comet has only one tail but it turns out that a comet has two tails.

~Halley's comet is the most famous comet ever observed.  Halley's comet comes close to earth around every 76 years.

~When comets orbit around the sun, the comet will shed small rocks which forms a dust trail or a meteoroid stream.  When earth passes through this stream it is called a meteor shower.

~Did you know it is possible for a comet to go extinct?  This happens when the sun's gravity breaks them up into smaller pieces if they pass by too closely.  Click here to see an example of a comet's death dive.

So there is the briefest explanation of a comet that I can provide.  Next up a look at Pluto.

Visit Khan Academy for How Our Solar System Was Formed.
Hank Green on youtube.
Youtube, Ried Reimers' the Oort Cloud: Believe it or not.