why all planets and stars are round shaped and?

Question

not in other shape say, triangle?

Answer 1

Mass drawn to it's center of gravity is most easily evenly distributed when it's a sphere. A triangle or square would produce areas of high potential energy (falling), so the mass would tend to shape itself into the lowest energy state (round, where all points of it's surface are equi-distant from the center of mass).

Answer 2

Once an object has accreted sufficient mass its gravity acts to pull it into a spherical shape.

Water droplets are round because of the surface tension of water. Gravity is such a weak force it plays very little role in the determining the shape of a water droplet. But even in interstellar space two atomic nuclei will tend to be attracted to one another--ever so slightly.

Clouds of interstellar gas tend to be inelastic. Their collapse is generally precipitated either through collision with another cloud--stars will form along the boundaries, or through a shock wave, such as a supernova, or through penetration by some mass. A black hole orbitting a galaxy will precipitate stellar formation as it passes through interstellar clouds.

For a typical star, gravitational collapse causes it to heat up, and shine. A star may glow a million years or so as a protosun before internal pressure and temperature rises high enough for fusion to occur.

In conclusion--gravity pulls moons, planets, and stars into round shapes. Ceres, largest of the asteroids, is fairly round due to its gravity. Deimos, smaller of the martian moons, is not all that round.

Answer 3

It is the most natural shape for something that accretes (collects together) from smaller pieces under the influence of gravity. It forms the lowest potential energy. There would have to be some intervention to get corners on objects that large.

Answer 4

because of the force gravity all the matter comes in the center and the all are not spheres but they are flattened at the poles the shapes are known as geoid

Answer 5

because an electron is shaped like that (spherical actually).