< Mentor Note -- thread moved to Astro forum from the Sci-Fi Fantasy forum > I apologise in advance if this comes across as hopelessly esoteric, but here goes: picture a 250 metre diameter sphere suspended in space (okay, in orbit round the Sun) with a surface temperature of 8,000 K. Now I'm aware that the brightness (light-signature?) of such an object would fall away quite rapidly over a given distance. Even so, I'd appreciate it very much if someone knowledgeable on the subject of optics could reveal to me how close an observer would need to be in order to perceive this radiant sphere as a naked-eye object. Also, if convention requires the answer to be in lux, lumens, watts, candle-power etc., is there some way to translate such metrics into absolute magnitude? Or is this like asking what the absolute magnitude might be of Piccadilly Circus or Times Square? Many thanks.