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Space

The Speed Of Light Is Not Instant

The Speed Of Light Is Not Instant

Until 1676, people believed light traveled across the universe instantly. Astronomer Ole Rømer shattered this idea by observing that eclipses of Jupiter’s moons happened later than expected as Earth moved away.

Rømer noticed the timing of Io's orbit around Jupiter shifted depending on Earth's distance from the planet. He realized this delay occurred because light takes longer to cover the extra space when the two planets are further apart. This simple observation proved light has a finite, measurable speed rather than being infinite. It was a massive leap forward that fundamentally changed our understanding of the cosmos.

Source: Rømer's determination of the speed of light

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