The Earth is a sphere with a radius of 6,371 km and, multiplying this value by 2, a diameter of 12,742 km. These values, however, consider the planet a perfect sphere, ignoring variations in relief.
The fact that the globe is actually slightly flattened at the poles — similar to an orange. This flattening is almost not noticeable: there are only 40 km of difference in the diameters measured in the direction of the Equator and in the North-South direction.
Humanity has known these measurements for more than two thousand years, thanks to the calculations performed by the mathematician Eratosthenes, born in Cyrene, present-day Libya. Current satellites show that the scholar got the circumference value wrong — whose formula is 2π times the radius — by just 500 km, something impressive considering the limitations of the time.
To get an idea of the size of the planet, we can compare the distance to the center of the Earth with distances on the surface. The 6,371 km of terrestrial radius would be equivalent to approximately 15 trips from São Paulo to Rio de Janeiro. In addition, the measurement is more than twice the distance between the closest points in Brazil and Africa: it is 2,839 km to the continent on the other side of the Atlantic.
What about the radius of other planets?
Earth is already immense with its radius of just over 6,000 km, but other measurements in the solar system are even larger. Uranus (25,362 km) has a radius four times greater, while Saturn is nine times Earth’s (58,232 km) . Jupiter, the largest planet in our system, has a radius of almost 70,000 km — 11 times that of Earth.
Our planet, however, is ahead of Venus, Mars and Mercury when it comes to size. Venus is only 300 km less in radius (6,052 km), but that of Mars is almost half (3,390 km) of ours, while that of Mercury is approximately one third (2,440 km). The radius of the dwarf planet Pluto is about 1/5 that of Earth.
