The earliest known mentions of spheres appear in the work of the ancient Greek mathematicians. Bubbles such as soap bubbles take a spherical shape in equilibrium. The Earth is often approximated as a sphere in geography, and the celestial sphere is an important concept in astronomy. Spheres roll smoothly in any direction. Since it was believed that the fixed stars did not change their positions relative to one another, it was argued that they must be on the surface of a single starry sphere. A logical conclusion of Togi, Togi Serif aims to function both in display and text size.