Why is the Solar System Flat?
Why Hacker News recommends it
HN commenters link it as a quick, intuitive explanation of angular momentum and why spinning clumps of matter flatten.
What it is
A minutephysics explainer on why the planets orbit in a flat plane. It shows how conserved angular momentum flattens a collapsing cloud of matter into a disk.
Recommended by 3 HN commenters across 3 different months, 2014 to 2025.
What Hacker News said
Strong rec TheCoreh · 2014-02 · on “The fastest pulsar spins at 716Hz; its equator spins at 24% the speed of light”
It has to do with the total angular momentum of a system composed of multiple smaller bodies. (Like the dust/debris cloud during solar system formation) This minute physics video (about the shape of the solar system) explains it probably better than I can put into words myself: [this video] The relevent part starts at about 1:03, but I recommend watching the whole thing.
Recommends igemnace · 2023-06 · on “Strong Solar Flare Erupts from Sun on Jun 20, 2023”
I like this video from minutephysics to get an intuitive sense for it: [this video] It addresses a different question (Why is the Solar System Flat?) but it touches on the question of why things spin when they clump together from gravity. An answer through the lens of my own understanding: it's just more difficult NOT to have angular momentum. If you have a lot of particles falling toward each other due to gravity, imagine how difficult it would be to set it up such that all of them fall straight into their collective center of mass. They'd have to be in a precise, orderly configuration (e.g. equally spaced apart on a unit sphere). Note that each particle affects each other particle -- if any one
Recommends orra · 2025-03 · on “Euclid finds complete Einstein Ring in NGC galaxy”
Indeed. And to elaborate: the random collisions which flattened the solar system (or galaxy) over billions of years all conserved angular momentum. Minute Physics have a nice video on this: [this video]