By: Jeremy Sun
Earth is not a perfect sphere but an oblate spheroid, meaning it is slightly flattened at the poles and bulges at the equator due to its rotation. This was first noted by ancient Greek philosophers and confirmed by scientists like Isaac Newton, becoming widely accepted in the 18th century. The shape can be observed through satellite data and precise measurements.
Geographer Bill Carstensen from Virginia Tech in Blacksburg explains that long before Columbus sailed, ancient Greek scholars like Aristotle suggested the Earth was round. They observed that ships sailing away appeared smaller and eventually vanished at the horizon, a phenomenon consistent with a spherical Earth.
Isaac Newton was the first to propose that Earth is not perfectly round but rather an oblate spheroid. Because of this bulge, the distance from Earth’s center to sea level is approximately 21 kilometers greater at the equator compared to the poles.
Our planet, however, isn’t shaped like an ideal oblate spheroid because its mass is distributed unevenly. Geologist Joe Meert from the University of Florida in Gainesville explains that areas with higher concentrations of mass exert stronger gravitational pull, leading to irregularities or “bumps” observed across the globe.
Earth’s shape evolves over time due to a range of dynamic factors. Internal shifts in mass alter gravitational anomalies, while mountains and valleys form and disappear through plate tectonics.
Occasional meteor impacts create craters on the surface. Moreover, the gravitational forces of the moon and sun not only produce oceanic and atmospheric tides but also influence tides within the Earth itself.
In addition, the changing weight of the oceans and atmosphere can cause deformations of the crust. To even out Earth’s imbalanced distribution of mass and stabilize its spin, the entire surface of the Earth will rotate and try to redistribute mass along the equator, a process called true polar wander.
Scientists use high tech methods to monitor the shape of Earth. They put thousands of GPS receivers on the ground to measure tiny changes in height. Another method, satellite laser ranging, uses lasers from ground stations to track satellites. This reveals variations in their orbits, showing where there are differences in gravity and how mass is spread within Earth.
Very long baseline interferometry uses radio telescopes on the ground to track distant radio waves, which helps detect movements in the positions of ground stations. Even though we know Earth isn’t perfectly round, figuring out its exact shape is complex and needs a lot of advanced technology.
Image Credit by Pixabay