Why the Erath is called an oblate sphere or a spheroid?

 The Earth is often referred to as an "oblate spheroid" or "spheroid" because its shape is not a perfect sphere but rather slightly flattened at the poles and slightly bulging at the equator. This shape is the result of the planet's rotation and the forces acting on it.

Here's why Earth is considered an oblate spheroid:

1.      Centrifugal Force: The Earth rotates on its axis, causing the equator to experience a centrifugal force due to the planet's rotation. This force causes material to be pushed away from the axis of rotation and toward the equator, resulting in a bulging at the equator.

 

2.      Equatorial Bulge: Because of the centrifugal force, the Earth is wider at the equator than it is at the poles. This bulging is relatively subtle, with the equatorial diameter being a few kilometers larger than the polar diameter.

 

3.      Measurements and Observations: Measurements of Earth's shape, obtained through techniques such as satellite observations, geodesy, and precise measurements of Earth's gravitational field, have confirmed that its shape is indeed slightly flattened at the poles and slightly bulging at the equator.

 

The term "oblate spheroid" or "spheroid" accurately describes this non-perfect spherical shape. It's important to note that while the Earth's shape is not a perfect sphere, the difference between its equatorial and polar diameters is relatively small compared to its overall size. This slightly flattened shape has implications for various geophysical and navigational calculations and has been well-documented through scientific observations and measurements.