On October 19th a once in a lifetime event will happen. Comet Siding Spring (C/2013 A1) will pass very close to Mars, one tenth the distance of the closest Earth-comet pass. While there is no chance of impact, NASA has moved some of its Mars orbiting satellite to be behind the planet is it passes through the comet’s dust tail in order to protect the equipment.
At predicted magnitude 11, it will be limited to large telescopes with camera or CCD. But its close proximity to Mars will make it an easy target to locate. Unfortunately for North America, the closest approach will take place 2:28pm EDT.