1. Luminosity: This refers to the total amount of energy a star emits per unit of time. A star's luminosity is directly related to its size and temperature. Larger, hotter stars have a much higher luminosity than smaller, cooler stars.
2. Distance: While a star might be incredibly luminous, its apparent brightness to us on Earth depends on its distance. The further away a star is, the dimmer it appears. This is similar to how a light bulb looks brighter up close and dimmer from a distance.
Therefore, a star can appear bright because it's inherently luminous, or because it's relatively close to us, or both.
