Jocelyn Bell Burnell's 1967 pulsar signal was first dismissed as man-made interference before confirmation as PSR B1919+21

In 1967, Cambridge postgraduate Jocelyn Bell Burnell noticed an anomalous, precisely periodic radio signal in her chart-recorder traces — "a bit of scruff" — which turned out to be the first detected pulsar. The signal first appeared in survey data recorded in August 1967, but because the chart-recorder paper had to be checked by hand, finding and pinning it down took roughly three months — the pulsations were captured on a fast recording only at the end of November 1967. Her supervisor Antony Hewish initially treated the source as man-made interference; the object briefly carried the tongue-in-cheek designation LGM-1 ("Little Green Man 1") before being confirmed as a natural rotating neutron star, catalogued as PSR B1919+21.

The episode is a canonical instance of a real signal nearly filed as instrument noise: the anomaly is only recognizable as a discovery after someone declines to attribute it to interference. That is the same signal-versus-instrument-error judgment call that governed the Antarctic ozone data eighteen years later — claim-antarctic-ozone-hole-first-reported-from-ground-dobson-readings-1985 and the correction of its own tidy legend, myth-nasa-software-discarded-the-ozone-hole. Across a completely different field (radio astronomy versus atmospheric chemistry), the shape recurs: the point where a true signal is separated from noise is exactly where discoveries hide or get lost.