You don’t have to be a scientist to know that stars shine. It’s what they’re known for. But how and why they shine was unknown for thousands of years, and only became clear in the 20th century, as humans puzzled out the power of nuclear fusion.
To understand how stars shine, it’s important to know one more basic fact about stars: they’re incredibly massive. The presence of that much material in one area gives rise to a gravitational force strong enough to dictate the path of planets billions of miles away. Close up, that gravity crunches atoms together. And squeezing two atoms into one creates a powerful burst of energy, as humans witnessed firsthand when they built their own fusion bombs. Stars spend most of their lives repetitively compressing two hydrogen atoms into a single helium atom – plus a lot of energy, which is released as light and heat.
