planets(1)

💫 planets — bestie's guide to yeeting celestial bodies around 💫

okay so real talk, this is planets(1), from the General Commands Manual section, and it's genuinely one of my fave little programs ever. sit down, grab a snack, we're doing gravitational physics 💖

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✨ NAME ✨

planets — gravitational simulation of planetary bodies 🪐✨

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🌸 DESCRIPTION 🌸

so basically planets is a lil interactive program for playing around with simulations of planetary systems. and the way that it's lowkey a perfect teaching tool for understanding how gravitation works on a planetary level?? obsessed. fr fr. 🧚

the user interface is designed to be simple enough that a fairly young kid can get some joy out of it 💅 and there's ALSO a special kid-mode aimed at very young children — and no cap, kid mode grabs the focus and converts key banging into lots of random planets. like, chaos mode activated, planets everywhere, iconic. 🎀

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🎀 KEYBINDINGS 🎀

🪐 Universe definition

• a — Add Planet
• j — Place random orbital planet
• r — Place random planet
• u — Undo (undoes the last planet insertion)
• e — Reset to empty universe
• g — Go Back (goes back to just after the last planet insertion)
• Mouse — Click on a planet to delete it 🫶

🔥 Physics

• b — Toggle bounce (experimental — yes bestie, experimental, we'll get to that)

🌈 Display control

• Cursor keys — Panning
• c, Space — Move display to center of mass
• x — Initiate center of mass tracking
• = — Zoom in
• - — Zoom out
• p — Toggle Pause
• o — Change all colors randomly (chaos. beautiful chaos.)
• t — Toggle Trace
• d — Double Trace Length
• h — Halve Trace Length
• Mouse — Drag a box around a set of planets to follow the center of mass of those planets

👑 Program control

• H — Display help dialog
• k — Display option dialog
• Ctrl-Shift-k — Toggle kid-mode. Kid mode locks the keyboard and mouse, so the only way to get out is to toggle kid-mode again to get out. 🚨

okay so real talk: kid mode is a trap if you don't remember the escape hatch. it locks your keyboard and mouse, and the ONLY way out is toggling kid-mode again. memorize Ctrl-Shift-k. that's your exit. periodt.

• l — Load Universe. After pressing l, press any other character to load the universe with that name. Universes are stored in ~/.planets/ .
• s — Save Universe. After pressing s, press any other character to save the universe with that name. Universes are saved in ~/.planets/ .
• q, Esc — Quit

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🔬 TECHNICAL DETAILS 🔬

ngl the actual math here is kinda slay. planets uses a fourth-order runge-kutta approximation for the simulation itself. ✨

planet bouncing is achieved by adding a repulsive force to planets at close quarters.

and the way planets is fairly flexible?? you can change the gravitational constant, the time-slice of the simulation, and even the exponent used in the gravitational law. yes bestie, the exponent. go wild. 💅

universes are saved in the ~/.planets directory, and they're simple human readable and editable files — so you can literally just open them up and mess with them yourself. no cap. 🦋

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💀 BUGS 💀

currently bouncing doesn't work very well unless you make the time-slice quite small. 😭

ideally, it would be nice to have a billiard-style bounce system, but it's not clear how to do this accurately in the presence of a strong gravitational field. so like... we're all just living with it for now. 🙈

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🫶 AUTHOR 🫶

planets was written by Yaron M. Minsky <yminsky@cs.cornell.edu> as a gift for his nephew, Eyal Minsky-Fenick. (a gift!! for his nephew!!! the way that's the sweetest thing ever, I'm literally tearing up 😭💖)

this manpage was contributed originally by Martin Pitt <martin@piware.de> for the Debian GNU/Linux system (but may be used by others). 🐧

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okay that's the whole thing bestie, you're fully caught up. this page is from April 20, 2003 and it lives under planets(1) — go add a planet for me, mwah 💅💖✨