Explaining The Universe on Instagram: "Refraction is the bending of light (or any wave) as it passes from one medium into another where its speed changes. For example, when light travels from air into water, it slows down because water is denser than air, causing the light ray to bend toward the normal (an imaginary line perpendicular to the surface). This effect explains why a straw looks “bent” in a glass of water, why lenses can focus light, and why rainbows form when sunlight refracts throug