* Nuclear Fusion: Stars produce energy through nuclear fusion. This is a process where lighter atomic nuclei (like hydrogen) combine to form heavier nuclei (like helium), releasing enormous amounts of energy in the process.

* Heat and Light: This energy is primarily released as heat and light. The intense heat generated within the star's core causes the outer layers to become extremely hot, radiating light across the electromagnetic spectrum, including visible light.

* Stars Glow: This is what makes stars glow. The light we see from stars is a direct result of the heat produced by nuclear fusion.

So, the heat produced by nuclear fusion is the fundamental reason why stars glow.