Yes, all spheres are similar in geometry. In mathematical terms, two shapes are considered similar if they have the same shape but may differ in size. Spheres meet this criterion because every sphere is perfectly round and all points on its surface are equidistant from its center. The ratio of corresponding dimensions (like radii or diameters) between any two spheres is constant, regardless of their size.
This means a small marble and a giant planet, both of which are spherical, are similar in geometry. Their proportions remain consistent, differing only by scale. This property makes spheres unique and consistent in the realm of three-dimensional shapes.