Last Sunday morning (May 22), Mars reached opposition with the sun, meaning the Red Planet, Earth and the sun were all arrayed in a straight line. But the moment did not mark Mars' closest approach to Earth. This Monday evening (May 30) at 5:35 p.m. EDT (2135 GMT), Mars will be the closest it has been to Earth since Oct. 5, 2005: 0.50321377 astronomical units (AU), or 46,762,695 miles (75,279,709 kilometers). (One AU is the average distance from Earth to the sun — about 93 million miles, or 150 million km.) Opposition and closest Earth approach occur on different days because the orbit of Mars is elliptical. When opposition occurred May 22, Mars was still approaching Earth on its orbital track, and will not reach minimum distance to Earth until May 30. After 5:35 p.m. EDT on that date, Mars will begin to recede from Earth. The graphic shows how Mars would appear viewed with a superb telescope at the exact instant of closest approach. The landing site of NASA's Opportunity rover is