Science is always an unfinished project. That’s what makes it so much fun. The process—collecting data, building models to explain how the world works, and then dethroning them with new models—is full ...

When our sun exhausts the hydrogen fuel in its core some 5 billion years from now, it will expand to become a red giant, engulfing the inner planets. The dynamics and possible outcomes of planetary ...

This article was updated Feb. 28, 2023. It was originally published March 1, 2000. Planetary gears can supply high levels of torque and high-speed reduction. They are also relatively compact compared ...