CAPE CANAVERAL, Florida - Mars, Earth and the sun will align on May 22, 2016 - an event that only occurs once every 26 months. This alignment is called "Mars Opposition" because Mars and the sun are on directly opposite sides of Earth. Eight days later on May 30, 2016, Mars and Earth will be nearest to each other in their orbits around the sun.
Mars Opposition on May 22
To viewers on Earth, Mars will rise in the east just as the sun sets in the west. Then, after staying up in the sky the entire night, Mars sets in the west just as the sun rises in the east.
An opposition can occur anywhere along Mars' orbit. When it happens while the red planet is closest to the sun (called "perihelic opposition"), Mars is particularly close to Earth. If Earth and Mars both had perfectly stable orbits, then each perihelic opposition would bring the two planets as close as they could be. Also, the orbits of Earth and Mars don't lie in quite the same plane. The paths the planets take around the sun are slightly tilted with respect to each other.
Mars' orbit is more elliptical than Earth's, so the difference between perihelion and aphelion is greater. Over the past centuries, Mars' orbit has been getting more and more elongated, carrying the planet even nearer to the sun at perihelion and even farther away at aphelion. So future perihelic oppositions will bring Earth and Mars even closer.
Some perihelic oppositions brings the two planets closer together than others. The 2003 opposition was the closest approach in almost 60,000 years that won't be seen again until August 28, 2287.
Mars Closest To Earth On May 30
Mars is over half a million miles closer to Earth at closest approach than at opposition. But you won't see much change in the diameter and brightness between these two dates. As Mars comes closer to Earth in its orbit, it appears larger and larger and brighter and brighter.
The best time to see Mars at its brightest is when it is highest in the sky, around midnight local time in May and a little earlier in June. Through a telescope you can make out some of the dark features on the planet, some of the lighter features and sometimes polar ice and dust storm-obscured areas showing very little detail.
After close approach, Earth sweeps past Mars quickly. So the planet appears large and bright for only a couple weeks. But don't worry if you miss 2016's close approach that brings the red planet just 46.8 million miles away from Earth. 2018's will be even closer at 35.8 million miles.
Photo and video credit: NASA/JPL