Stellar brightness refers to the amount of light a star emits and how bright it appears from Earth. This brightness can be measured in two ways: absolute magnitude, which is the brightness of a star at a standard distance of 10 parsecs, and apparent magnitude, which is how bright a star looks from our planet. Different factors affect a star's brightness, including its size, temperature, and distance from Earth. For example, a massive star like Betelgeuse may appear bright even if it is far away, while a smaller star can seem dimmer despite being closer.