Toowoomba, Australia, July 16th. A person asked a very interesting question. “I am puzzled why planets, stars, and moons are round (when) other sizeable objects such as asteroids and meteorites are irregular in shape.” -Lionel Young, 74, Launceston, Tasmania.
This is a great question, Lionel, and a good observation! When we observe the solar system, we see objects of all sizes, from tiny dust particles to huge planets and the sun. A common theme of these objects is that they are large (more or less) are round, and the small is irregular. but why? Gravity: The key to making large objects round. The answer to the question of why large objects are round lies in gravity. The attraction of an object always points to its center of mass. The larger the object, the greater its mass, and the greater its attractive force.
For solid objects, this force cancels out the force of the object itself. For example, the downward force you receive due to gravity will not push you towards the center of the earth. Because the ground also pushes you back, it has too much power to immerse you in it.
But when you consider that all objects tend to rotate or hover in space, the situation becomes more complicated. When an object rotates, a point on its equator (a point between the two poles) will receive a slightly reduced attraction. Compared with the place near the pole. The result is that the perfect sphere expected in the hydrostatic equilibrium becomes an “oblate sphere” in which the object at the equator is wider than the poles. This applies to our rotating Earth, which has an equatorial diameter of 12,756 kilometers and a pole diameter of 12,712 kilometers.
The faster an object rotates in space, the more pronounced the effect. Saturn is less dense than water, rotating around its axis every 10 and 1/2 hours (compared to the 24-hour cycle on Earth). As a result, it is spherical degree is much lower than that of the earth. But to put it simply, the reason why large celestial bodies are spherical (or almost spherical) is because their mass is large enough that their gravitational force can exceed the force of the material that composes them.