orbital-mechanics

If the Sun vanished right now, we'd have 8 minutes of sunlight left. Then darkness, plummeting temperatures, and Earth drifting into interstellar space.

There are over 8,000 active satellites orbiting Earth right now. Here's how they stay up and what they do.

There may be more rogue planets — wandering worlds without stars — than there are stars in the galaxy. If one drifted into our solar system, even a brief passage could destabilize planetary orbits and reshape Earth's climate for millennia.

Tidal locking occurs when a body's rotation period equals its orbital period, so one hemisphere permanently faces its partner. The Moon is locked to Earth, which is why we always see the same face, and the same effect probably shapes planets around red dwarf stars.

A ringworld would not break any law of physics, but it would break every material we know. The spin arithmetic shows exactly where each megastructure sits on the ladder from buildable to impossible.