Your use of the word "dense" there is a little misleading. At the default view the scale of each satelite pixel looks roughly 20km wide.

Unintentional sick burn on Saturn.

Green is active, orange is debris or dead sats. When a GEO sat runs out of life / power / fuel the operators are supposed to move it out of the main corridor to make room, so often they are in the same ring but higher or lower

I'm not familiar, what is the law, that we cannot use authentication cookies or google/twitter analytics cookies?

Making an educated guess as a layperson, besides some satellites that are geosynchronous but not geostationary, I'd assume those are primarily old geostationary satellites in graveyard orbits - when they're EOL, satellites in those orbits are supposed to perform a small boost out of them, usually adding a few hundred km to their orbit's radius (GEO is about 36,000km in altitude, so a few hundred km is relatively small). Then, without station keeping, I believe they should naturally precess around the Laplace plane, which will range between roughly Earth's equator and the ecliptic plane (the plane of Earth's orbit). At GEO altitudes the Laplace plane is about 7.2 degrees inclined from the equator. I believe that would mean, starting at the equator with an inclination of 0 degrees, these satellites should precess to about 14.4 degrees and back to 0 over several decades (excluding other perturbations, of course).

I found this online which would seem to confirm at least the mechanics: https://amostech.com/TechnicalPapers/2013/Orbital_Debris/ROSENGREN.pdf

From what I could find that’s probably the band of decommissioned geosynchronous satellites. Apparently they’ll slowly match the orbital plane of the earth around the sun.

https://space.stackexchange.com/questions/12528/why-is-the-ribbon-of-decommissioned-geosynchronous-satellites-skewed

those are mostly red and orange, so that also confirms the other comments' guesses:

Wow thanks! If you like this, on Monday I'm planning to release an update that will let you rewind the viewer all the way back to 1959 and see the first launch of Sputnik. Then let it play forward to today sped up so you can see the growth of satellite counts. Also a new public API to fetch the TLEs from any date. I'm hoping this will let folks do interesting stuff with all that data - maybe AI training or research projects etc.

Wow thanks so much!

Yes, so I'm taking every telescope/radio/radar reading I'm allowed to redistribute and then collecting them into a time series database and fetching the most recent reading for each sat into a text file. That's the TLE download in the public API. Then I use Rust WASM to propagate those readings into positions that are synced with the viewer time. This allows us to very roughly forecast where they will be for the next couple days.

It's cool because it's too much data to transfer over the network, so we only transfer the most recent reading and then calculate positions live in the browser.

I know it blew my mind too when I first started building this! It's such a cool project to get to build!