This past weekend marked Mars opposition, the midpoint in a 26-month cycle where Earth races towards and then away from the red planet.
Opposition is the point where Mars and the sun are opposite each other with Earth directly in the middle. This was most evident on Saturday as Mars rose in the east just as the sun set in the west.
Additionally, at noon Monday, Earth and Mars were at their closest since January 2010, a mere 62.6 million miles apart.
Astronomers usually skip the big numbers and refer to planetary distances in more manageable astronomical units or AU. 1 AU is the average distance of the Earth to the sun. That 62.6 million-mile distance to Mars equates to 0.67 AU. At this distance, the light hitting your eyeball as you gaze upon Mars Tuesday night will take 5.6 minutes to travel to the Earth.
In mid-April 2013, Mars will be in conjunction with the Earth. This is the other point where Mars and Earth line up, but this time the sun is the middle, blocking our view. This is also where Mars is at its furthest point from Earth, a distance of 2.43 AU. Light will take just over 20 minutes to reach Earth and Mars will appear about one quarter as large in our night sky as it does this month.
This conjunction point starts the whole 26-month cycle, called apparition, all over again. The next opposition will occur in April 2014.
The exact point in time of Mars opposition has passed. The planet is only getting further away as Earth speeds around the sun like a faster runner lapping an opponent. But don't let that discourage you from going out an enjoying the beautiful sight of the reddish orange planet. It will look pretty much the same either with the naked eye or with a backyard telescope and will be visible all night will be for the next four weeks. It's very bright and easy to spot not just because it's close but also because the full disk of the planet is lit by the sun.
All this positioning information is more than just interesting trivia.
Space agencies like NASA plan launches of exploration missions around these points in the celestial calendar. Last November's launch of the Mars Science Laboratory was timed to take advantage of this week's opposition. The relative positions of Mars and Earth help improve mission efficiency and success.
Why launch three months ahead of this event? Why not launch to Mars at the moment the planets are closest? It takes nine months to reach Mars, even when the planets are relatively close. It's also not a matter of pointing the rocket to the red dot in the sky and pressing the button. Wayne Gretzky put it better than any mission planner could have: “Skate to where the puck is going to be, not where it has been.”
For more information about events along Mars orbit, see http://spider.seds.org/spider/Mars/mars2012.html