Stars are massive balls of hot gas that produce light and heat through nuclear fusion. They shine continuously, although their brightness can vary over time due to various factors like stellar evolution, pulsations, and eclipses.
The idea of a star only glowing every 100 years is a fictional concept. Perhaps you're thinking of a specific story or legend, or perhaps it's a creative idea for a story.
If you can provide more context about where you heard this idea, I might be able to offer a more specific answer.
