A star pours out a fixed power, its luminosity L. By the time the light reaches us it has spread over a sphere of surface area 4πd², so the radiant flux we receive is F = L / (4πd²). Move the detector and watch the flux collapse as the distance grows: double the distance and only a quarter of the flux arrives.
MissionPush the detector far from the star and watch the flux collapse, then bring it close and watch it surge. Same power, spread thinner over 4πd².Streak 0Best 0
If you move the detector from d to 2d, the flux F it receives becomes:
distance d2.0 d₀
relative flux F / F₀0.250
received flux F = L / (4πd²)—
The luminosity sets how much light leaves the star; the distance sets how thinly it is spread. A standard candle has a known L, so measuring F reveals d.