Final answer:
Explaining that light from the Sun takes about 8 minutes and 20 seconds to reach Earth offers the correct understanding of the distance at the speed of light.
Step-by-step explanation:
When it is stated that Earth is an average of only 8 minutes and 20 seconds from the Sun at the speed of light, this refers to the fact that light from the Sun takes this amount of time to reach Earth (Option C). This does not suggest that Earth travels around the Sun at the speed of light, nor does it imply that the Sun's gravity does not affect the speed of light or the duration of Earth's rotation.
Rather, it is a measure of light's travel time from the Sun to Earth. To further explain, the Earth is approximately 150 million kilometers away from the Sun. This distance is also known as one Astronomical Unit (AU). During its orbit, Earth travels at an average speed of about 110,000 kilometers per hour, which equals approximately 66,000 miles per hour after conversion.
The speed of light is a universal constant in a vacuum, calculated to be roughly 299,792 kilometers per second. Early astronomers like Ole Roemer and later Albert Michelson made significant progress in measuring this value accurately. Michelson's method, for instance, involved a set of rotating mirrors that determined the time taken for light to reflect and return over a set distance. Gravity can affect the perception of time and the propagation of light, as mentioned by Einstein's theory of general relativity, which notes the curvature of spacetime around massive bodies like the Sun.