Supernovae — stellar explosions that briefly outshine their galaxies — act as cosmic beacons for astronomers: by knowing their true brightness, we can calculate distances. But the light from these beacons gets redder and dimmer as it passes through interstellar dust — a cosmic fog. Previously, it was unclear whether this redness was tied to the explosion itself or solely to the dust.

Analysis of nearly a thousand supernovae using spectroscopy (splitting light into colors) and precise brightness measurements (photometry) revealed that the explosions of white dwarfs — ultra-dense stellar remnants — always have the same color. All the observed redness comes from dust.

Now it's clear: correcting for dust makes supernovae ideal "standard candles." Astronomers can more accurately track the expansion of the universe and refine the parameters of dark energy.