disconnected fantasy worldbuilding detail:
a world that has a sun, but because magic it does not emit light, but rather some other thing. The moon converts that thing into light and it is bright enough to mostly function as a sun for daylight purposes. But it’s still a moon, with a lunar cycle, and so how much light there is varies over the month, making the new moon a time of extended darkness and the full moon _too_ bright
magical artefacts can function as mini-moons and also turn sunstuff into light, but of course they only work during sun-day.
The first satellite photographs of the far side of the Moon disproved the consensus view that the Moon was made of lightstone. The far side of the moon, beyond the area visible through libration, was dark. Only the parts of the Moon that Earth could see emitted light.
This resulted in some rather amusing theorization that perhaps the far side of the Moon was coated heavily with impact debris, which was blocking the light more thoroughly than impact debris on the near side. The Moon had to have debris on the near side; otherwise what was there to explain the patterns that appeared on its face?
The Luna and Surveyor programs showed capably that it was a material spread across the near side of the Moon — now colloquially termed “the light side” —that caused it to shed light on Earth.
When Apollo 11 landed on the Moon, astronauts Armstrong and Aldrin experienced difficulty walking on the Lunar surface. As the Surveyor cameras confirmed, the surface of the Moon was a near-uniform scattering of bowling-ball-sized lightstones, bigger than any stone seen on Earth. Almost perfectly spherical, as near as their instruments could determine. Of a uniform size. A uniform weight, too — in the light lunar gravity, an unassisted human could lift the bowling-ball-sized objects. They only weighed 40 pounds.
With a density near 20 grams per cubic centimeter, they would’ve been impossible to lift on Earth. The sample return mass budget was blown; Apollo 11 left a large amount of hastily-assessed nonessential equipment behind on the Lunar surface, including the Hasselblad 70mm EDC and the 16mm Maurer Data Acquisition Camera. They brought the film back from the Moon; it was uniformly overexposed.
A detail not seen by the Surveyor cameras was that the lightstones had serial numbers.
A crash program was instituted to send a probe into Solar orbit; it was shortly discovered that the light of the Sun was intercepted at the Earth-Sun L1 point by a parasol of simply gargantuan size. Beyond the parasol’s shade was light of a frequency that matched spectral lines seen from other stars. The Garden hypothesis was confirmed: the Solar system was special.
Since light from the other planets did not reveal the characteristic spectral patterns seen in trans-parasol sunlight (later termed “direct sunlight”), a telescopic survey was undertaken of other planets’ L1 points; these revealed similar parasols, though not every planet had a corresponding moon. The asteroid belt was revealed to be even stranger: each individual asteroid had its own parasol.
Direct sunlight was found to have spectra before only seen in laboratory conditions.
Seven decades later, Moon-worshipping terrorists landed on the Earth Parasol and demanded a ransom; the ransom negotiations broke down when a Sun-worshipper embedded in the Moonist cult prematurely detonated the explosives. The parasol was unmoved.
Shortly after the first human-crewed probe left the shade of Earth’s parasol; the crew and instruments observed the arrival of an independent parasol that kept pace with their ship. It remained synchronized during several trajectory adjustment burns, and disappeared once the ship entered the shadow of the Martian parasol.
Unlike the Earth parasol, this lesser parasol allowed such light to penetrate as is emitted by lightstones. This light did not charge lightstones brought by the crew, nor did exposure to the light shed by the parasol covering Mars. These lesser parasols appear to filter raw sunlight to only those frequencies emitted by lightstones. Only exposure to the shadow of the Earth parasol charges lightstones.
When mirrors were put in orbit around Mars to attempt to lighten its nights with sunlight, the parasol grew to shade them.
Centuries passed before the distance conjecture was disproven: A human-crewed ship sent to the planets of Alpha Centauri was accompanied by a parasol during its entire mission, and the parasol split and grew as necessary to shade all human population. A cautious test determined that any single human was enough to warrant a parasol; this was true of any Terran biota.
To this day we still do not know why parasols shield us from the light of the Sun, or how. Only photons coming directly from the Sun are absorbed by the parasols; every other source of photon is passed with complete transparency. Excepting Earth, every planet’s parasol is a Lesser parasol. A whole-sky survey with lightstone-derived telescopic cameras has revealed no Greater parasols.
Lightstones cannot be manufactured by any art or science known to humanity; their quantity appears to be finite. The serial numbers follow no obvious pattern in no known language.
It seems, therefore, that the spread of humanity into space was the proximate cause of the death of magic as a discipline warranting serious study. Its practice is effectively limited to Earth and the Moon, as there are no supplies of lightstones or their power source yet discovered in the galaxy.
By leaving Earth, we left behind an old science and developed a new.