sir, we continue talk about planets and its orbit but my doubt is why every planet is a sphere and why it is not triangle,rectangleor any other shape.

because of gravity. All of the matter thats on a planet is being pulled to the core of that planet. The places where is less matter pulls more matter because it is closer to the core.

So at the places where there's more matter, it the opposite situation: there will be less matter attracted and therefore there stuff crumbles easier and that matter is being pulled to areas that are closer to the core. That process causes planets to become round.

There will be slight variation in shape if the planet has a weird gravitational field.

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regards

Ramesh