The phenomenon in the atmosphere that can cause rainbows is known as refraction of light. When sunlight passes through water droplets in the air, it bends and splits into a spectrum of colors. This process occurs due to the varying speeds of light in different media, resulting in the formation of a circular arc displaying the colors red, orange, yellow, green, blue, indigo, and violet. Rainbows typically occur when sunlight strikes water droplets after rainfall. Understanding this optical phenomenon involves principles of physics and atmospheric conditions.