When, exactly, did the astronaut set foot on the moon? No one knows. //

And yet for all that precision, no one can say with absolute certainty when, exactly, Neil Armstrong first set foot on the moon. //

The night of the moon landing, NASA told the press that Armstrong had stepped onto the lunar surface at 10:56:20 p.m., and The New York Times reported that same time stamp on its front page the next morning. The real-time transcription of the mission’s air-to-ground voice transmission suggests that Armstrong took the step sometime between 10:56:43 and 10:56:48. And when NASA’s official Apollo 11 mission report went public in November 1969, it pinpointed first contact at five seconds earlier, at 10:56:15. //

Heiko Küffen, a German software engineer and space enthusiast, first came across this discrepancy in 2009, while trying to design a homemade real-time tracker that he could use to relive the moon landing for its 40th anniversary. //

To synchronize the transcripts and the recordings, Küffen made what he calls “reasonable assumptions,” which nearly a decade later he has yet to see contradicted. Armstrong, he found, first set foot on the moon at 10:56:25—closer, in other words, to the almost universally dismissed time given to the press that night than to the time produced by the mission report’s months-long analysis.