Massive space mirrors could be 40 times brighter than the full moon, astronomers warn. 'It will be worse than big cities like London'

Astronomers have warned that the deployment of massive space mirrors could produce illumination up to 40 times brighter than the full moon, a level of night‑time brightness that would surpass the glow of large urban areas such as London. The scenario, described in a Space article, suggests a fundamental shift in the appearance of the night sky for observers worldwide. The brightness threat stems from commercial “sunlight on demand” concepts, including a California startup that secured approval earlier this year to launch a 59‑foot orbital mirror.

Proponents argue the mirrors could increase nighttime power generation by reflecting sunlight to ground‑based solar panels. MIT Technology Review cautions that the mirrors could jeopardize the night sky, but reporting stops short of quantifying mitigation strategies or regulatory oversight. The Telegraph‑Journal notes astronomers’ concerns without providing details on potential impact assessments.

What remains unclear is which agencies will govern brightness limits, how ecosystems might respond, and whether any mitigation technology is under development.