On August 27th, around 12 am. The distance between Mars and Earth will be 56 mill km. Bringing the Planet closest to our orbit, It will be visible with the naked eye!
Much has been made of the fact that the August 27th encounter with Mars is the closest in some 60,000 years. Neanderthals were the last to observe Mars so favorably placed. This is true. It’s also a bit of hype. Mars and Earth have been almost this close many times in recent history.
Some examples: Aug. 23, 1924; Aug. 18, 1845; Aug. 13, 1766. In each case Mars and Earth were approximately 56 million km apart.
Astronomers call these close encounters “perihelic oppositions.” Perihelic means Mars is near perihelion – its closest approach to the sun. (The orbit of Mars, like that of all planets, is an ellipse, so the distance between the sun and Mars varies.) Opposition means that the sun, Earth and Mars are in a straight line with Earth in the middle. Mars and the sun are on opposite sides of the sky. When Mars is at opposition and at perihelion – at the same time – it is very close to Earth.
August 27 is indeed the best perihelic opposition since the days of the Neanderthals, but it scarcely differs from other more recent ones. That’s fine because all perihelic oppositions of Mars are spectacular.
http://www.nasa.gov/vision/universe/watchtheskies/18jun_approachingmars.html