AboutJames Gort Expertise Questions on observational astronomy, optics, and astrophysics. Specializing in the evolution of stars, variable stars, supernovae, neuton stars/pulsars, black holes, quasars, and cosmology.
Experience I was a professional astronomer (University of Texas, McDonald Observatory), lecturer at the Adler Planetarium, professor of astrophysics, and amateur astronomer for 42 years. I have made numerous telescopes, and I am currently building one of the largest private observatories in Canada.
Publications StarDate, University of Texas, numerous Journal Publications
Question Hi James. How long would it take, on average (considering that Earth and Mars might be in different stages of orbit), to travel to Mars at the speed of light?
Answer Hello Lee,
This is a very difficult question to answer "correctly", and much depends on what you mean by "on average". First, the quick (and dirty) answer: The earth is an average of 8.3 light-minutes from the sun (take an average distance of 93 million miles, divided by 186,000 miles per second). Mars is an average of 1.5 times further from the sun than earth is. So at its closest approach to earth (neglecting the fact that the orbits are not circles, since we're talking averages), Mars is 1.5 - 1.0 = 0.5 times the distance of earth to the sun, or 4.15 light-minutes. At its farthest approach to earth, Mars is 1.5 + 1.0 = 2.5 times the distance of earth to sun, or 20.8 light-minutes. The answer is someplace in between. The simplistic approach is to take the average of 20.8 and 4.1 and you'll get 12.5 light-minutes. So it will take you, "on average", 12.5 minutes to reach Mars travelling at the speed of light.
But the trick is, we can't take a simple numerical average! Because both planets are in orbit, their relative spacing does not vary linearly. We need to take a "time average" and come up with a more accurate answer.
As I said, that's not easy, but I welcome you to try. You'll have to use some calculus and (if you really want a good answer), the exact orbital elements of both planets. Have fun!
