# Just How Far Is It From Earth To Mars?

Alan McStravick for redOrbit.com - Your Universe Online

If you´ve ever had an inquisitive child ask you how far Mars is from Earth and you were unsure how to answer then, you are not alone.

On their individual courses around our Sun, Mars and Earth follow an elliptical orbit. Imagine two race cars traveling on two different tracks at differing speeds. This analogy helps you visualize how sometimes these two planets are close together while at other times they are, quite literally, on opposite sides of the Sun. As a result of these celestial trajectories, the distance between Earth and Mars is ever changing, minute to minute, second to second.

This fact makes the efforts of scientists and engineers all the more fascinating. Take into consideration the numerous Mars study and exploration missions of late. The timing and precision required to launch a vehicle into space and aim it at another traveling planet is, at times, mind boggling. A mission like this can only be undertaken because scientists can trace and predict the exact distance between Earth and Mars at any given time.

As just mentioned, the planets´ orbits are not circular and travel instead in an elliptical, oval-like orbit. When any orbiting body is at its closest point to its sun, it is said to be at its perihelion. The outer reaches of a planet´s orbit, farthest from the Sun, is called the aphelion. For space mission experts, the optimal timing for missions occurs when both Earth and Mars are on the same side of the Sun, with Mars at its perihelion and Earth at its aphelion.

When Earth and Mars are at the point at which they are closest to one another, it is known as opposition. For the Earth-bound observer, opposition has been reached when Mars appears as a bright red star in the sky. Mars becomes one of the brightest objects in the heavens during this time, with its luminescence rivaling that of both Venus and Jupiter.

When Mars and Earth are at opposition and Mars is visible to the naked eye, the distance between the two planets is theoretically 34 million miles. Of course the use of the term "theoretical" is not an accident, as the planets have never actually been that close to one another in recorded history. We have to go back to 2003 to see the last known closest approach. This took place in the 2003 opposition, during which Mars was the closest to Earth it had been in some 50,000 years.

While scientists have compiled the next several Mars oppositions through the year 2020, the one this author is looking forward to will take place in 2018. On July 27 of that year, Mars will be at its closest point since its 2003 opposition. On that day, Mars is expected to shine bright red in our sky.