Why the Sun is so Stable

Feedback loops, oscillation, and self-regulating systems in nature and technology

Don Cross
The Startup
Published in
8 min readNov 14, 2019


Photo by Mor Shani on Unsplash

Consistent, high-quality output. It sounds like an excerpt from a glowing employee performance review, doesn’t it? Anyone would be proud of such an assessment. But no matter how hardworking and consistent some human workers may be, the Sun has us all beat.

Our Sun has been producing a reliable supply of planet-warming, life-giving sunlight for eons. All life on Earth traces back more than 4 billion years, in an uninterrupted chain, to some mysterious single-celled creature. Powering a habitable planet this long, year in and year out, requires more than endurance. It also requires a certain degree of stability.

If the Sun’s power output fluctuated too much, the Earth’s oceans would alternately freeze and boil, repeatedly killing all life on the planet. Even if life restarted each time the oceans returned to a tolerable temperature, the interruption would prevent the evolution of intelligent, self-aware creatures like us.

Evolution is simply too slow. It took approximately two billion years for the first multicellular organisms to appear. Before then, all living things were single-celled creatures like bacteria and algae. Another two billion years elapsed before animals with sophisticated brains evolved. Our existence implies that the Sun has been sufficiently stable over a long enough period of time to maintain an ever-habitable Earth.

The Sun’s stability is not a given. Astronomers have studied thousands of stars in individual detail and millions in statistical aggregate. Not all stars are as stable as the Sun. Some stars vary in brightness, at times doubling the amount of power they produce before dimming again. Of these variable stars, some alternate between high and low power with a clocklike regularity. Others do so in an unpredictable, arrhythmic pattern.

However, the Sun is not an oddball either. It is a typical star. There are plenty of other stars like it that burn steady for billions of years or more. Why the difference? Let’s talk first about how the Sun works and why it’s so stable. We’ll come back to the variable stars later.

How the Sun Generates Power