No, it is not accurate to say that every planet, moon, and star has a spherical shape. While many astronomical objects, such as planets and stars, tend to have a roughly spherical shape, this is not true for all celestial bodies.
The process by which astronomical objects acquire a spherical shape is primarily due to gravitational forces acting on them over long periods of time. Under the influence of gravity, objects in space tend to collapse inward and settle into a state of hydrostatic equilibrium, where the gravitational forces pulling inward are balanced by the pressure pushing outward. This equilibrium configuration often leads to a roughly spherical shape.
However, it's important to note that not all celestial bodies start with a non-spherical shape and gradually become spherical. The initial shape of an astronomical object can depend on various factors, such as its formation mechanism, composition, and history of collisions or tidal interactions.
For example, during the formation of a planet or moon, collisions of smaller bodies and the subsequent merging and accretion processes can lead to the development of a roughly spherical shape. Similarly, stars form from collapsing clouds of gas and dust, which can also result in a spherical shape due to gravitational collapse.
That being said, there are celestial bodies that deviate significantly from a perfect sphere due to factors like rotation, tidal forces, or the presence of prominent surface features such as mountains or valleys. Moons with irregular shapes or asteroids with non-spherical forms are examples of such celestial bodies.
In summary, while many astronomical objects tend to have a roughly spherical shape due to the influence of gravity, the specific shape of each object depends on its individual history, formation processes, and external influences. Not all objects necessarily undergo a process of being shaped from a non-spherical form to a sphere over billions of years.