Could a disco ball moon turn Earth's orbit into a hall of mirrors?
Imagine the Moon replaced by 3,012 massive, glass-tiled mirrors. As sunlight hits these thick, silvered surfaces, it creates intense concentrations of light called caustics. From low orbit, these reflections could act like tiny, secondary suns, fundamentally altering the light and radiation reaching our planet.
The hypothetical structure consists of 3,012 mirrored tiles, varying in size from 100 to 150 square kilometers. Each tile is composed of 10 km thick glass with an index of refraction of 1.56, featuring a silvered backing. Because the sunlight must first pass through this thick glass, the tiles act as a filter, significantly reducing the amount of ultraviolet radiation that reaches the Earth's surface.
The optical behavior of these tiles depends heavily on the observer's perspective and the angle of light. When viewed from a low altitude, such as the International Space Station—which sits roughly 420 km from the moon's surface in this scenario—the projection of a mirror tile appears larger than the sun. This creates 'caustics,' concentrated points of light that function effectively as tiny suns. However, from a great distance, the tiles appear smaller than the sun, resulting in less intense brightness.
The physics of these reflections are governed by Fresnel reflection. As the angle of incidence approaches 90 degrees, more light is reflected off the first surface of the glass rather than penetrating it. This reflected light remains full-spectrum. While these concentrated beams are incredibly bright, they would never exceed the surface temperature of the sun, which is approximately 6,000 degrees.
While this model assumes a 2.1-hour orbital period relative to Earth, the sheer scale of the construction is physically impractical. A real-world version of such a massive object would likely avoid heavy, thick rims in favor of lightweight girder work and Mylar films, rather than the over-engineered, 'Death Star' style structure described in this thought experiment.
Source: What if the Moon was a Disco Ball?
