Do planets move along the ecliptic?

Answer 1

Because that's the way gravity works.

Every closed orbit of one mass traveling around another mass is an ellipse.

It may be slightly eccentric or greatly eccentric, but it's an ellipse.

If you drop a shovel of gravel out in space, and let the gravitational force

between each pair of stones pull them around for a while, what happens ?

Some of them drift away and are never seen again. Some of them sink towards

other stones, circle once, and then go shooting off to infinity and never come

back. And some of them settle into closed orbits around others.

All of the closed orbits are ellipses, because that's the way gravity works.

Some are more eccentric, some are less eccentric. Some are long, skinny orbits,

with the central body way off at one end, like long-period comets. Some are

moderately eccentric orbits, like Mercury and Pluto have. Some orbits have such

small eccentricity that you can't tell them apart from circles, like those of Venus

and Neptune.

If there happens a one-in-a-billion, highly improbable, remote chance occurrence,

where all the details just happen to be perfect, and a body just happens, by the

remotest coincidence, to have just exactly the perfect combination of distance,

tangential velocity, radial velocity, and energy when it's captured into its closed

orbit, then the foci of the ellipse would exactly coincide, the major and minor

axes would be equal, the speed of the 'planet' in its orbit would never change,

its distance from the central body would be constant ... the orbit would be a circle !

Sure it's possible, just like it's possible to balance a spherical rock on the point of

a pin, and it's possible for all the air molecules in the room to move in the same

direction at the same time and all pile up in the corner and leave you across the

room with nothing to breathe. It's possible, but very unlikely.

That's the way gravity works.

Answer 2

There are a lot of forces pulling on planets: for example the earth.

The sun pulls on earth, causing an ecliptic movement.

The sun is not the only one; the moon pulls on the earth as wel and even other planets who are far away from the earth cause small flaws in the ecliptic.

Answer 3

All of the planets appear close to the ecliptic in the Earth's night sky, but none of them

stays right on it. The band in the sky, along the ecliptic, that all the planets appear to stay

in is the 'zodiac'. Since the sun, the planets, and even the moon are always somewhere

in that band, it was thought to have some magical significance, and Astrology is all about

what happens in that band around the sky.

Answer 4

The ecliptic is the plane of the Earth's orbit around the Sun. So the Sun and the Earth are always on the ecliptic.

Most of the other planets have orbits that are within a few degrees of the ecliptic, which probably means that that was the plane of rotation for the primordial stellar nebula that formed the Sun and the solar system.