How Al-Biruni estimated Earth's circumference from a mountain

Al-Biruni estimated Earth's size from one mountain

Al-Biruni measured the height of a mountain and the angle down to the horizon from its top. With those measurements and geometry, he could estimate Earth's circumference from one place instead of making observations at two distant locations.

Roman culture outlasted imperial rule

The Western Roman Empire’s fall in 476 ended political unity and military control, but Roman culture did not disappear at once. Archaeological and cultural traces continued in some areas as late as the eleventh century.

The deep ocean stores far more heat

~50× the mixed layer’s heat capacity

The ocean’s deep layers have about 50 times the heat capacity of its mixed layer. They respond over millennia, delaying the effects of climate change. As the ocean warms, its expansion also contributes to sea-level rise.

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How Al-Biruni estimated Earth's circumference from a mountain

Al-Biruni estimated Earth's size from one mountain

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