Is it true that planets always follow the same path? Aren't they influenced by (as they get near to) other planets or to other planet's moons?
I mean, don't they all have gravity fields? So, shouldn't they all influence each other?
http://www.youtube.com/watch?v=9R5P9Y9gR…
I mean, don't they all have gravity fields? So, shouldn't they all influence each other?
http://www.youtube.com/watch?v=9R5P9Y9gR…
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Planets do NOT always follow the same path.
Earth has a wobble because it is in orbit around the barycentre ( = centre of mass) of the Earth-Moon system. It is the barycentre of the system that has a nice orbit around the Sun.
But even this "nice orbit" is not a closed loop, as it does not retrace the same path. The influence of the other planets (especially Jupiter and Saturn) causes random changes of up to 500 km per year in the orbital radius. However, because the interference is periodical, the whole thing does balance out over very long periods. Therefore, if you look at long periods (millions of years), the orbits are considered stable.
Comets, being smaller and having very elongated orbits, will often be infludenced by planets, especially when they pass very close (one planet never really passes very close to another planet). Therefore, comet orbits are not considered stable (in general).
Earth has a wobble because it is in orbit around the barycentre ( = centre of mass) of the Earth-Moon system. It is the barycentre of the system that has a nice orbit around the Sun.
But even this "nice orbit" is not a closed loop, as it does not retrace the same path. The influence of the other planets (especially Jupiter and Saturn) causes random changes of up to 500 km per year in the orbital radius. However, because the interference is periodical, the whole thing does balance out over very long periods. Therefore, if you look at long periods (millions of years), the orbits are considered stable.
Comets, being smaller and having very elongated orbits, will often be infludenced by planets, especially when they pass very close (one planet never really passes very close to another planet). Therefore, comet orbits are not considered stable (in general).
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typo- Thank YOU so
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Yes, they are influenced by other planets. That's why we have meteorites - Jupiter is big enough to disturb asteroids out of the asteroid belt and occasionally send them this way.
It is also, I believe, why there is an asteroid belt in the first place and not another planet there.
But the major planets have been in fairly stable orbits for millions of years. SInce gravity falls off as the square of the distance, the influence of, say, Jupiter on Earth's moon is very small.
There are also stable points (Trojan points) 120 degrees away from a planet in its orbit. So there a a couple of small bunches of asteroids in orbit with Jupiter, where dust and rocks tend to accumulate, and conversely, away from those points, orbits are unstable and things don't stay there.
It is also, I believe, why there is an asteroid belt in the first place and not another planet there.
But the major planets have been in fairly stable orbits for millions of years. SInce gravity falls off as the square of the distance, the influence of, say, Jupiter on Earth's moon is very small.
There are also stable points (Trojan points) 120 degrees away from a planet in its orbit. So there a a couple of small bunches of asteroids in orbit with Jupiter, where dust and rocks tend to accumulate, and conversely, away from those points, orbits are unstable and things don't stay there.