The black dot is not a sphere, but a plane circle \ x0d \ x0d \ Extension: \x0d\ x0d \ 1. Definition of a circle: \ x0d \ A circle is a geometric figure. When a line segment rotates around one endpoint on a plane, the trajectory of the other endpoint is called a circle. By definition, compasses are usually used to draw circles. The radius length of the inner circle of the same circle is always the same, and the circle has countless radii and diameters. A circle is a figure with axial symmetry and central symmetry. The axis of symmetry is the straight line where the diameter lies. At the same time, the circle is a "positive infinite polygon" and "infinity" is just a concept. The more sides a polygon has, the closer it is to a circle in shape, perimeter and area (that's why people call a circle a regular polygon). So there is no real circle in the world, and the circle is actually just a conceptual figure. \x0d\\x0d\2。 Definition of Sphere \x0d\ Definition: A figure composed of all points whose distance from a fixed point in space is less than or equal to a fixed length is called a sphere, and the figure shown above is a sphere. \x0d\ Sphere is a three-dimensional figure with continuous surface, and the geometric figure surrounded by sphere is called sphere. \x0d\ There is no absolute sphere in the world. Absolute spheres exist only in theory. \x0d\ But in weightless environment (such as space), droplets will automatically form an absolute sphere. \x0d\\x0d\ To sum up, the black spot is not a sphere, but a plane circle.