Why isn't Everest's summit the farthest point from Earth's centre?

Everest's summit is not the farthest point from Earth's centre because the Earth is not a perfect ball. Its spin makes it bulge at the Equator, and a mountain sitting on that bulge starts from a higher base. The winner is Chimborazo, a volcano in Ecuador just one degree south of the Equator. It is only 6,263 metres high, about 2,600 metres lower than Everest, yet its summit is 6,384.4 kilometres from Earth's centre, 2.1 kilometres farther out than the top of Everest, which sits nearly 28° north.

The bulge is small but real. Earth is about 43 kilometres wider at the Equator than from pole to pole, so someone standing at sea level at a pole is 21 kilometres closer to the centre than someone at sea level on the Equator. Shrink the Earth to a globe one metre across and the difference would be just 3.3 millimetres, too small to see. So why doesn't Chimborazo count as the highest mountain? Because heights are measured from sea level, and the oceans bulge too.

People once argued fiercely about this shape. In the 18th century, the astronomer Jacques Cassini believed Earth was stretched toward the poles. France sent two expeditions to measure it, one to Lapland and one to the Equator in what is now Ecuador. They proved the opposite: Earth is flattened at the poles. Those measurements later helped create the metre.