Final answer:
The rays of sunlight moving straight from the sun perpendicular to Earth are known as parallel rays, due to the ray model of light concept in geometric optics.
Step-by-step explanation:
The rays of sunlight that move straight from the sun and strike the Earth's surface perpendicularly are known as parallel rays. This is because the Sun is a distant light source, about 150 million kilometers away, causing the light rays that reach the Earth to be nearly parallel to each other. When viewed from different locations on Earth, these rays would appear almost perfectly aligned, and hence they are modeled as traveling along straight lines. In geometric optics, this conceptualization of light propagation is referred to as the ray model of light, which is a useful way to describe the behavior of light when it travels through empty space, various medias, or after being reflected from a mirror.