How does Kristen Lippincott explain the equation of time?

Kristen Lippincott said John Flamsteed, working at Greenwich in the 1670s, tested whether the Earth turns at a constant speed against an accurate clock. He found the sun runs fast or slow against a clock depending on the time of year. Around 4 November a sundial reads about 16 minutes ahead of a clock, and in February about 15 minutes behind. The equation of time is Flamsteed's table of that gap, telling you how far a clock and the sun disagree on any day.

• Ptolemy had assumed a constant rotation, but no clock had been good enough to check it.

Source: our own transcription of the episode. The full conversation is on In Our Time (2026-10-12). Read the whole episode summary →

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