How come planets orbits arounds the soon are flat?

[Tigermisu]

As well as our moon, how did they all manage to be equatorial?

[gmpd2000]

the orbit of the moon isn't equatorial...

As your question.

It's probably because they were all formed of the same disk.

[nothke]

A long long time ago, in our galaxy, right here beside us, before sun existed, the whole solar system was just this solar dust cloud (popularly called a nebula). And so, since all the matter attracts due to gravity, this cloud started to collapse into it's center (where the net gravity is strongest).. And so... Just like when you release the lid (is that the right English word?) in your bathtub, and the water starts spinning in one direction (direction is irrelevant and depends on circumstances), due to inter-molecular collisions, that is the same reason why that collapsing dust starts also spinning.. And in the same way the pizza guy makes the thin disc of dough by spinning it on the finger (lets imagine all pizzamakers do that), in this way the dust cloud forms a disc, In the mean time the dust compresses in the center so much that it is capable of sustaining fission (star), and the disc, due to "clearing up" of it's neighboring boulders become rocky planets. As for gas giants, these are gas clouds that didn't have enough mass to sustain fission.

In reality, none of the planets have the same inclination, and that is mostly due to this "clearing up", or collisions with objects, that ultimately make planets. Scientist today think that moon was formed when a huge asteroid collided with Earth. That collision might've also changed inclination slightly.

And that is exactly why the galaxy is a disc too just on a bigger scale.

Sorry for bad English, but in short, that's it

PS. And by "equatorial" you probably mean in-line with Earth's orbit around sun. It's not aligned with equator, neither is equator with the Earth's orbit around sound. Earth has 23 degrees axis tilt. The extreme case might be Uranus, whose axis tilt is 97 degrees, almost normal to the orbit towards the sun.. This is most probably also due to collisions and early formation

And how do we know all this actually happened?? We look at other stars and nebulae and we see how they are forming.

Edited April 27, 2013 by nothke

[Xeldrak]

This has to do with the way our solar system was formed, it started as a cloud of dus.......oh, just read nothke's post, he took away my answer