Processing nature of comets

[alext87]

We have just been learning about elliptcal orbits of comets and there was a computer model of elliptcal orbits and it showed them slow changing orbital paths so that the oval shape of the orbit slowly rotates around a point and eventually the comet/planet maps out its original path.

 

How can this be if we continue to see the same comets flying past the Earth every 100years or so surely we should only see them every 1000years or so?

 

not very clear...SORRY but I'm very confused.

[formulaterp]

There are various reasons why the orbital path of a comet may change over time. The most common are gravitational preturbances due to close passes of planets, especially Jupiter, and the thrust induced by venting as the comet approaches the sun. Generally these result in small differences on each pass. I'm not sure why you think this precludes our ability to spot them every 100 years or so. Perhaps you can clarify.

 

Some more info:

 

Comets aren't as regular as you might think, that is I wouldn't set your watch by them. For example everyone knows about Halley's comet. It was made famous because Sir Edmund Halley deduced that numerous sightings over time were in fact the same comet, traveling along a regular path about every 76 years. Using that information he predicted it's next arrival. However, the comet did not arrive until TWO YEARS after the predicted date. This is not unusual.

 

Halley, despite its orbital period being nearly equal to a human lifetime, is considered a short period comet. We have identified several hundred, perhaps thousands of these. Long period comets, such as Hale-Bopp have orbital periods in the several thousands of years. It's almost impossible to say how many of them there are since a given civilization may only see it once.