A looping animation of a stylized sunrise and sunset over a layered landscape. The scene uses several inline SVG gradients, including a radial gradient for the sky and two linear gradients for the terrain, each with animated `<stop>` color values. A circle representing the sun moves vertically via an SVG `<animate>` element on its `cy` attribute. All animations repeat indefinitely with a 15-second duration, with the code relying solely on native SVG and SMIL APIs, without any external JavaScript libraries.