Space Geometry

[clayrog]

This is more of a generic question about the geometry of things we see in space. It is a curiosity (to me) that I have wondered about for over 50 years. Our solar system with the known planets, asteroids, and comets appears to be relatively flat--all the objects revolving about our sun are generally in the same plane -- as depicted in science books and models. Likewise, for planets with multiple moons.(?) The pictures of galaxies from the (amazing) Hubble images show that they too are generally flat, with a bulge at the center, which could be a result of high gravity(?). On the other extreme of scale in our world, science depicts atoms with the electrons swirling around the nucleus in a three dimensional pattern in multiple planes. So, I'm curious about why the difference? Would it be expected that the geometry of atoms be like we see in space?
Note, I am only an engineer, and have never studied astronomy or astrophysics, but have always been curious about how these things work. What's it all about?

[geckzilla]

Science doesn't depict atoms with electrons swirling around the nucleus, illustrators do. It's a simple way of representing an atom that's not necessarily realistic. As for the solar system, planetary systems, and disc-shaped galaxies, those can all be explained with angular momentum. For a quick understanding of angular momentum, I recommend watching a quick video. It's how I learned what it is, anyway.

Click to play embedded YouTube video.

[Chris Peterson]

This is more of a generic question about the geometry of things we see in space. It is a curiosity (to me) that I have wondered about for over 50 years. Our solar system with the known planets, asteroids, and comets appears to be relatively flat--all the objects revolving about our sun are generally in the same plane -- as depicted in science books and models. Likewise, for planets with multiple moons.(?) The pictures of galaxies from the (amazing) Hubble images show that they too are generally flat, with a bulge at the center, which could be a result of high gravity(?). On the other extreme of scale in our world, science depicts atoms with the electrons swirling around the nucleus in a three dimensional pattern in multiple planes. So, I'm curious about why the difference? Would it be expected that the geometry of atoms be like we see in space?
Note, I am only an engineer, and have never studied astronomy or astrophysics, but have always been curious about how these things work. What's it all about?

Systems that have a large part of their total mass orbiting in the same plane got that way because at some point in their evolution the material density was high enough that they behaved like fluids, with the particles interacting with each other (typically via the electromagnetic force) and transferring angular momentum between each other. That results in everything ending up in a plane, and the ejection of a lot of material from the system. Once a system is in that state, however, if the density drops to the point where fluid dynamics goes away (as with planetary systems and galaxies), there's a gradual drift away from planarity. Lots of material in the Solar System now orbits at high inclinations, and over billions of years the planets will drift to different inclinations. The central bulge of spiral galaxies is made up of stars in random inclinations, and flat galaxies evolve into ellipticals, with little or no planar structure.