The speed of light in a vacuum is approximately 299,792,458 meters per second (or about 186,282 miles per second). This value is often rounded to approximately 300,000 kilometers per second for simplicity.
To determine how long it takes for a beam of light to reach us from Mars, we need to know the distance between Earth and Mars at a given time because the distance varies due to the elliptical nature of the planets' orbits around the Sun. On average, Mars is about 225 million kilometers (about 140 million miles) away from Earth.
Using the speed of light, we can calculate the time it takes for light to travel from Mars to Earth or vice versa by dividing the distance by the speed of light. Let's use the average distance of 225 million kilometers as an example:
Time = Distance / Speed
Time = 225,000,000 kilometers / 300,000 kilometers per second
Time ≈ 750 seconds
So, it takes approximately 750 seconds, or 12.5 minutes, for light to travel from Mars to Earth (or vice versa) when the distance is about 225 million kilometers. However, it's important to note that this value can vary depending on the positions of Earth and Mars in their respective orbits around the Sun.