Final answer:
When light passes from space into the atmosphere, it changes speed, which is a process known as refraction. This physical phenomenon occurs due to the variation in indices of refraction between different media.
Step-by-step explanation:
When light passes from space into the atmosphere, it changes speed in a process known as refraction. This occurs because as light moves from a medium with one index of refraction (such as the vacuum of space) into another medium with a different index of refraction (such as Earth's atmosphere), its speed changes. This change in speed is accompanied by a change in direction, because the path of the light bends at the boundary between the two media. Refraction is a fundamental concept in physics and is responsible for a variety of phenomena, including the bending of light as it passes through lenses and the underwater distortion of objects viewed from above the surface.