The Human Archives
Orbital diagram from the 1676 publication of Ole Rømer’s measurement
Rømer's Diagram, 8 of 10 in TimeIdea 1 of 3: The Hesitation of Light
Time 007—008

Rømer's Diagram

1676 CE

From the archiveTime10 artifacts
From the record · 01 / 03

The Hesitation of Light

For most of history, light was assumed to be instantaneous. If you opened your eyes, you saw the world as it was right now. In 1676, Ole Rømer noticed a glitch in the clockwork of the solar system. The eclipses of Jupiter's moon Io happened 'late' when Earth was far from Jupiter, and 'early' when Earth was close.

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For most of history, light was assumed to be instantaneous. If you opened your eyes, you saw the world as it was right now. In 1676, Ole Rømer noticed a glitch in the clockwork of the solar system. The eclipses of Jupiter's moon Io happened 'late' when Earth was far from Jupiter, and 'early' when Earth was close.

He realized this wasn't an irregularity in the moon's orbit, but a delay in the signal itself. Light took time to cross the extra distance. The universe was not a single, simultaneous 'now', but a patchwork of delayed signals.