Final answer:
Light can travel from a source to Earth through empty space, through a medium, or by reflecting off an object. Light is modeled as traveling in straight lines called rays.
Step-by-step explanation:
Light can travel from a source to Earth in three ways. The first is by traveling through empty space directly, such as light from the Sun reaching the Earth's upper atmosphere. The second way is by traveling through a medium like air or glass, typically transitioning from one medium to another. The third way is by reflecting off an object, like a mirror. Light is modeled as traveling in straight lines called rays, which may change direction when encountering objects or transitioning between materials, but it continues in a straight line or as a ray throughout its path.