How Big Is The Earth?

What is Earth's diameter and circumference?

According to NASA, Earth's average diameter is about 7,918 miles (12,742 km), and its circumference at the equator is about 24,901 miles (40,075 km). Earth's surface area is about 196.9 million square miles, of which roughly 71 percent is covered by water and 29 percent by land. Of all the rocky planets in our solar system, Earth is the largest. Among all planets, Earth ranks fifth behind Jupiter, Saturn, Uranus, and Neptune.

Is Earth a perfect sphere?

No. Earth is technically an oblate spheroid, meaning it's slightly squashed at the poles and slightly bulged at the equator. The equatorial diameter is about 7,926 miles, while the pole-to-pole diameter is about 7,900 miles. That's a difference of roughly 27 miles, or about 0.3 percent. The bulge is caused by Earth's rotation: the spinning motion creates a centrifugal effect that pushes the equator outward over billions of years.

How does Earth's size compare to other planets?

Earth is the largest of the rocky planets but tiny compared to the gas giants. Earth's diameter is about 95 percent of Venus's, but Jupiter's diameter is about 11 times Earth's, and you could fit roughly 1,300 Earths inside Jupiter by volume. Even Saturn could hold about 760 Earths. By contrast, Mercury is only 38 percent of Earth's size, and Mars is about 53 percent. Among the solar system's eight planets, Earth lands solidly in the middle.

How was Earth's size first measured?

Around 240 BCE, the Greek mathematician Eratosthenes calculated Earth's circumference by comparing the angles of shadows in two cities at noon on the same day. He came up with about 25,000 miles, remarkably close to the modern value of 24,901 miles. Eratosthenes pulled this off without telescopes, satellites, or even a precise unit of distance. Modern measurements use satellite ranging, GPS, and laser altimetry, but the basic answer hasn't changed much in over 2,200 years.