The primary unit used to measure luminosity in physics is the watt (W), which quantifies the rate of energy transfer. Specifically, luminosity refers to the total amount of energy radiated by an object per unit time. In the context of astronomy, luminosity can also refer to the intrinsic brightness of stars and is often expressed in units relative to the Sun, known as solar luminosities (L☉). Understanding luminosity is essential in fields such as astrophysics, where it helps determine the properties and distance of celestial bodies.