When viewed from outer space, celestial bodies such as the Earth, Sun, and other planets appear to be circular in shape due to several factors:
Gravity and rotation: Massive celestial bodies like the Earth and the Sun have enough gravity to pull their matter toward the center, resulting in a roughly spherical shape. The force of gravity acts equally in all directions, causing matter to settle into a shape that minimizes its potential energy. Additionally, the rotation of these bodies contributes to the overall spherical appearance.
Centrifugal force: The rotation of celestial bodies creates a centrifugal force that counteracts the force of gravity at the equator. This effect leads to a slight bulging at the equatorial regions and a flattening at the poles, making the overall shape more oblate spheroid (slightly flattened sphere) than a perfect sphere.
Hydrostatic equilibrium: Celestial bodies with sufficient mass and internal pressure achieve hydrostatic equilibrium. Gravity compresses the material toward the center, while the pressure generated by the internal heat counteracts gravity. This balance results in a spherical shape.
Lack of significant atmosphere: When viewing celestial bodies from space, there is typically no significant atmosphere to scatter or distort light. In the absence of atmospheric effects, the true shape of the celestial body becomes more apparent, appearing as a circle or a spherical shape.
It's worth noting that while celestial bodies generally appear circular when observed from space, close-up observations and measurements can reveal variations and irregularities on their surfaces, such as mountains, valleys, and other geological features.