May 30th.


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.)

- See more at: http://www.space.com/3297...8fDwK.dpuf

When lighting conditions are exactly right, Olympus Mons can be spotted by keen-eyed observers on Earth, but the mighty Valles Marineris has never been seen from here (although the huge canyon complex has been mapped in detail by satellites in orbit around Mars).

Regular observers of Mars soon become familiar with the normal patterns of light and dark on its surface, known as "albedo markings." If you observe Mars over a few hours, you will see these markings appear to move slowly across the disk, as Mars rotates just slightly more slowly than Earth, a full rotation taking 24 hours, 37 minutes and 23 seconds. Because of Mars' slightly longer day, if you observe Mars at the same time on successive nights, the markings will seem to move.

- See more at: http://www.space.com/3297...8fDwK.dpuf