1. Intrinsic Luminosity: This refers to the total amount of light a star actually emits. Stars vary greatly in size and temperature. Larger, hotter stars produce far more light than smaller, cooler stars. A star like Sirius, which is about twice the size of our Sun and significantly hotter, shines much brighter.

2. Distance: Even if two stars have the same intrinsic luminosity, the one that is closer to us will appear brighter. This is like how a car's headlights seem dimmer the farther away it is. Stars that are very far away, even if they are incredibly bright, may appear faint or even invisible to our naked eye.