Across all wavelengths of light, the Sun is brighter than the Moon. Until we went to the highest energies and saw a gamma-ray surprise.
If you look at all the objects detectable in Earth’s skies, including both naturally occurring bodies as well as artificial satellites, it should come as no surprise that the Sun appears as the brightest object of all. The Sun, after all, produces its own light, sustainably powered by nuclear fusion in its core. That core-generated energy helps keep the Sun from contracting under its own gravitation, but also propagates to the Sun’s edge, the photosphere, where the Sun emits radiation over a wide range of wavelengths that correspond to a temperature of around 6000 K. Although the Moon is the second-brightest object in most wavelengths of light, it only appears so bright because of its very close proximity to Earth. From an intrinsic point of view, most of the Moon’s light is merely reflected light from the Sun.
Although this was first shown to be true in visible wavelengths of light, the 20th century revealed that the same physical process held true across a wide variety of other wavelengths. The Sun is the brightest object in Earth’s skies, followed distantly by the Moon in second place, as seen from…
