Tabby's Star: The Flickering Sun That Made Astronomers Say the A-Word

2026-07-26 · Signals & Sounds · 8 min read

Between 2009 and 2013, NASA's Kepler space telescope held a single patch of sky under continuous watch. Its field covered roughly 150,000 stars near the constellation Cygnus, and its task was to catch the faint, regular winks that betray a planet crossing in front of its sun. The dimming involved is minuscule. Even a giant the size of Jupiter blocks only about one percent of its star's light, and the instrument was built to measure changes far smaller than that. The volume of data was too large for the mission team to inspect by eye, so a citizen science project called Planet Hunters invited the public to scan the light curves. It was these volunteers, ordinary people at their keyboards, who kept circling one star in the archive and leaving the same baffled notes beside it. The star was KIC 8462852, an F-type main sequence star about 1,470 light-years away, slightly hotter and larger than the Sun and in every other respect unremarkable.

Its light did not behave like anything else in the catalogue. Instead of a shallow dip repeating on a fixed schedule, the brightness collapsed in ragged, asymmetric plunges. Around day 792 of the mission the star lost about 15 percent of its light. Around day 1519 it lost a staggering 22 percent. Around and between those events came a cluster of smaller irregular dips, some lasting a few days, others stretching over weeks, arriving at intervals with no discernible rhythm. Some fell steeply and recovered slowly, others did the reverse. A planet produces the same tidy dip on the same rigid schedule because it is a sphere on a fixed orbit. Whatever crossed this star was blocking close to a quarter of its light, at unpredictable times, in shapes no orbiting sphere could make.

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