Mars and Saturn Conjunctions

About this pairing

Mars and Saturn are similar in brightness much of the time, both around magnitude 1 to 0, though Mars brightens dramatically near its close approaches and can briefly far outshine Saturn. The contrast in color, the warm orange of Mars against the paler gold of Saturn, is the easiest way to tell them apart.

Both planets wander the full zodiac, so a Mars-Saturn conjunction can appear anywhere along the ecliptic and at any time of night. They line up about every two years on average; the table below gives the exact dates, the zodiac sign, and how close each pass runs.

A telescope shows Saturn's rings during any of these meetings, while Mars, much smaller in apparent size, shows little more than a tiny disk except near its closest approaches. For where every planet sits tonight, see the Today in the Sky dashboard.

Watching this pair

Think of this one as the connoisseur's conjunction. Nothing here dazzles; instead you get two similar points of roughly first-magnitude light, one warm orange, one pale gold, close enough to compare in a single glance. It is the best natural test of how well your eyes read star color, and a fine excuse to show someone that planets have colors at all.

The two-year rhythm belongs almost entirely to Mars. Saturn creeps through a single zodiac constellation for a year or more at a time, very nearly a fixed landmark, while Mars runs its whole orbit in under two years and sweeps past like a runner lapping a walker. Whether a given meeting is bright or modest depends on where Mars stands in its own cycle of approaches to Earth.

Photographing Mars and Saturn

This is a quiet pairing to photograph, and that is its charm. Neither planet is bright, so a tripod and a modest telephoto do the work, capturing the subtle color difference the eye can only just detect. There is no glare to fight and no twilight deadline; the meeting can fall high in a dark sky at any hour, so you can take your time over the exposure.

Because neither planet is bright, give the exposure a little longer, a second or two at a moderate ISO, to let the colors register, and keep the pair clear of the horizon haze that would mute them. Saturn's rings stay beyond the short lenses that frame a conjunction and take a very long lens or a telescope to show at all, so as with the other Saturn pairings the photograph records the meeting and the color contrast rather than planetary detail. A frame or two on successive nights shows the faster-moving Mars sliding past the near-stationary ringed planet.

Where the colors come from

The color difference this pair shows off has a physical cause worth knowing. Mars looks orange because its surface and airborne dust are rich in oxidized iron, rust in the literal sense, which reflects red light and soaks up blue. Saturn's paler gold comes from a deep atmosphere of hydrogen and helium capped by ammonia clouds and tinted by traces of other compounds, a whole cloud deck returning sunlight rather than a solid surface. Two very different worlds happen to land near the same modest brightness, which is what lets the eye weigh their tints against each other.

The roughly two-year gap between meetings comes down to the pace of Mars. Saturn, far out on a 29-year orbit, barely shifts against the stars from one year to the next, so the interval is set almost entirely by how long Mars needs to circle back to Saturn's slowly drifting position, a little over two years. The exact spacing wanders from one meeting to the next as both planets run through their yearly retrograde loops.

Which of the two looks brighter is itself worth watching, because it changes from meeting to meeting. Saturn holds fairly steady near first magnitude, dimming a little as its rings close toward edge-on and brightening as they open, while Mars swings far more widely with its distance from Earth. At a conjunction that lands within a year or so of a Mars opposition, the red planet can arrive clearly the brighter of the two; at one that falls when Mars is near the far side of its orbit, Saturn takes the lead and Mars is a modest ember beside it. Noting which wins, and by how much, is a simple way to sense where Mars stands in its cycle of approaches without any instrument at all.