On July 28, 2018, we’re just one day past Mars opposition. In other words, yesterday Earth flew between Mars and the sun. What a wonderful event!
When Mars is at opposition, the red planet lies opposite the sun in Earth’s sky. At such times, Mars rises in the east around sunset, climbs highest up in the sky around midnight, and sets in the west around sunrise. If you look for Mars tonight, you’ll see that’s it’s still shining brilliantly and will continue to do for months to come. Mars is now ascending in the east as the sun is sinking below the western horizon.
Mars comes closest to Earth every other year, around the time of opposition. Around now, Mars shines at its brilliant best in our sky. Has Mars passed closest to us? Not yet. Mars actually comes closest some days following its July 27 opposition, on July 31.
Oppositions of Mars are far from equal. That’s because Mars’ eccentric (oblong) orbit carries this world about 26 million miles (43 million km) closer to the sun at perihelion (nearest point in its orbit) than when Mars swings out to aphelion (its farthest point).
Oppositions that closely coincide with Mars at perihelion are much brighter and spectacular than distant oppositions that coincide with Mars swinging out to aphelion. That makes sense. When we pass between Mars and the sun – and Mars is closest in its orbit to the sun – then Mars is closest to us.
This year’s opposition of Mars is a super one, with Mars coming to within 35.78 million miles (57.59 million km) of Earth on July 31, 2018.
The historically close opposition of Mars on August 28, 2003, found Mars at 34.65 million miles (55.76 million km) from Earth. This was the Earth’s closest approach to Mars since the Stone Age. The last time Mars came closer to Earth was nearly 60,000 years ago, on September 24, 57,617 B.C., when the red planet was 34.62 million miles (55.72 million km) distant.
In contrast, the very distant opposition of March 3, 2012, placed Mars at 62.62 million miles (100.78 million km) away.
Close (or distant) oppositions recur in periods of 15 to 17 years. So we’re now having another close opposition of Mars some 15 years after the historically close encounter on August 28, 2003. Mars will next present an extra-close opposition on September 15, 2035, though it won’t be as quite close as the opposition of August, 2003.
Very similar Martian oppositions take place every 79 years (15 + 17 + 15 + 17 + 15 = 79). These 79-year cycles repeat with only a delay of 2 to 5 calendar days. The super-close opposition of Mars in the year 2082 will fall on September 1, 2082. But once again, Earth and Mars won’t come as close as they had in August 2003.
There is a more exact cycle of 284 years (79 + 79 + 79 + 15 + 17 + 15 = 284). The Martian opposition that comes 284 years after August 28, 2003 will fall on August 29, 2287. This time around, Mars will actually come closer to Earth than it did during its historically close encounter with Earth in August 2003.
Because the Martian orbit is getting more eccentric (oblong), the closest oppositions will actually come closer to Earth, and the farthest oppositions will actually become more distant. The computational wizard Jean Meeus figures that from the years 0 to 3000, Mars will come closest to Earth on September 8, 2729 (55.65 million kilometers) and farthest away on March 6, 2832 (101.50 million kilometers).
Want to know more about close and far Martian oppositions? Click here.
While the time is at hand, enjoy the close appearance of Mars in Earth’s sky during July and August of 2018.
Bottom line: Oppositions of Mars are far from equal. This post explains why Mars has near and far oppositions and shows why the 2018 opposition is a particularly good one.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.