The brightness of an astronomical object is typically measured using its apparent magnitude. The apparent magnitude is a measure of how bright an object appears from Earth, and it takes into account the object's distance from Earth and its intrinsic brightness.

The sun has an apparent magnitude of -26.74, which means it is incredibly bright. The moon's average apparent magnitude is -12.6, making it the second-brightest object in the night sky, after the sun.

However, the moon's brightness can vary depending on its phase. At its full phase, the moon has an apparent magnitude of -12.74, making it nearly as bright as the sun. However, at its new phase, the moon is not visible from Earth, so its apparent magnitude is undefined.

The moon's brightness is also affected by the Earth's atmosphere. The atmosphere can scatter and absorb sunlight, which can reduce the moon's apparent brightness. This effect is particularly noticeable when the moon is near the horizon, as the sunlight has to travel through more atmosphere to reach our eyes.

Overall, the moon is a very bright object in the night sky, and its brightness can vary depending on its phase and the Earth's atmosphere.