The Federation, Mercury.
Mercury was one of the planets in the Solar System with a very thin atmosphere. As a result, light shone directly on the planet with only a slight degree of deflection and dissipation. Therefore, Mercury's skies weren't as blue as the skies of Earth. It was completely pitch-black, aside from the light from the sun and other stars.
It was akin to a streetlamp in the middle of the night. The lamp itself was a bright, luminous entity, casting a bright light over whichever spot it shone on, but that didn't mean that the sky wasn't still dark.
There had been plenty of artificial lighting on the former Mercury. As the designated location for the construction of the array formation, the Federation had made a series of complex and complicated modifications to the planet. It had an artificial sun and the protection of the Solar System Array Formation. Mercury had gradually developed into a Federation base throughout the years!