In astronomy, luminosity is not quite the same thing as brightness. Luminosity measures the total amount of energy emitted&lt;/u/l&gt; by a star or other astronomical object in SI units of joules per second, which are watts. A watt is one unit of power, and just as a light bulb is measured in watts, so is the Sun, which has a total power output of 3.846×1026 W. This number is the basic metric used in astronomy: it is known as 1 solar luminosity, the symbol for which is formula_1.
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