Explaining The Universe on Instagram: "A circle is a perfectly round, two-dimensional shape where every point along its edge is the same distance from its center. This constant distance is called the radius, and the full distance across the circle through the center is the diameter, which is twice the radius. The line all the way around the circle is called the circumference. Circles are found everywhere in nature and human design—from planets and ripples in water to wheels and clocks. In math a