Why do planets go retrograde?
No planet ever turns around. Retrograde motion is what a planet's path looks like from a moving Earth: when one of the two overtakes the other, the planet seems to stop, drift backward against the stars for weeks or months, stop again and carry on.
Mars's next loop: it stops and turns back on 10 Jan 2027 and turns forward again on 1 Apr 2027, with opposition on 19 Feb 2027.
Mars's real path against the stars, twice a day from the ephemeris: longitude across with east to the left, as the sky looks facing south, latitude up from the ecliptic. It drifts west to east, stops, backs up through the hatched shadow zone, stops again and moves on, tracing a loop because its latitude changes while it turns.
The overtaking lane
Earth and Mars both circle the Sun in the same direction, Earth on the inside track and faster. Once every lap Earth catches up and passes. For the weeks around the pass, the line from Earth to Mars swings backward across the stars, the way a slower car seems to slide back against distant hills as you overtake it.
Follow the nine numbered sight lines on the strip above the orbits, which magnifies their directions. They march east, bunch up, step back west, bunch up again and march east: that backward step is the retrograde.
Real heliocentric positions, one a day, from the ephemeris. The nine sight lines are evenly spaced through the window and run from Earth through Mars. The stars are so far away that only a sight line's direction counts, so each direction is carried out to the zodiac ring from the Sun by a faint ray, and the strip on top spreads the nine directions out, one row per date, east to the left.
Slowing to a stop
A station is a speed of zero.
Mars does not flip from forward to backward. Seen from Earth it slows over weeks, from up to 0.55° a day in this window, until its motion along the zodiac drops to zero on 10 Jan 2027. That standstill is the station retrograde.
Then it creeps backward, at most 0.40° a day, around the moment Earth passes it, slows to zero again at the station direct on 1 Apr 2027 and picks up speed. The shadow before and after is the stretch it spends crossing the same degrees forward: the shadow period.
How far Mars moves along the zodiac each day as seen from Earth, from the ephemeris. Above the line it moves forward (eastward), below it backward. The stations are the two days the speed passes through zero: the planet seems to stand still.
Loops, zigzags and S-curves
The shape is set by the tilt of the orbit.
If every orbit lay in one plane, a retrograde would be a planet backing up along a single line. Orbits are tilted slightly against Earth's, so while a planet turns it also drifts north or south of the ecliptic. During this retrograde Mars moves between 3.2° and 4.5° of latitude, enough to open its path into a loop.
Where in its tilted orbit the planet happens to be decides the shape: crossing the ecliptic mid-turn gives a zigzag or an S, sitting above or below it gives a loop. The slow outer planets back up only a few degrees (2.4° for Pluto on average); Venus and Mars back up about 16° and 16.4°.
Each path runs from the start of the pre-shadow to the end of the post-shadow, east to the left as on the sky, computed daily from the ephemeris. Every cell has its own scale: the arc is how many degrees of longitude the retrograde covers, and LAT ×N marks a cell whose latitude is stretched N times so the shape can be seen.
Mercury and Venus do it the other way round
For the inner planets, Earth is the one overtaken.
Mercury and Venus orbit inside Earth's orbit and faster. Their retrogrades happen when they catch up with Earth and pass between us and the Sun, at inferior conjunction. Venus does it next on 24 Oct 2026, at 0.27 AU, in the middle of its 3 Oct – 14 Nov 2026 retrograde.
That is why an inner planet's retrograde falls when it is lost in the Sun's glare, while an outer planet's falls at opposition, when it is opposite the Sun and at its brightest. The geometry is the same overtaking, seen from the other lane.
How often each planet turns back
Once per lap of Earth.
| Planet | Comes round every | Retrograde lasts | Arc retraced | Current or next |
|---|---|---|---|---|
| Mercury | 116 days | 22 days | 13.4° | 24 Oct 2026 |
| Venus | 584 days | 42 days | 16° | 3 Oct 2026 |
| Mars | 780 days | 74 days | 16.4° | 10 Jan 2027 |
| Jupiter | 399 days | 121 days | 9.9° | 13 Dec 2026 |
| Saturn | 378 days | 138 days | 6.8° | 26 Jul 2026 |
| Uranus | 370 days | 152 days | 4° | 10 Sep 2026 |
| Neptune | 368 days | 158 days | 2.8° | 7 Jul 2026 |
| Pluto | 367 days | 162 days | 2.4° | 6 May 2026 |
A planet turns retrograde once each time Earth laps it, or it laps Earth: its synodic period, computed from the two orbits. Lengths and arcs are averages over every retrograde from 1900 to 2100.
Beyond Mars the pattern is simple: the farther out a planet is, the closer its retrograde comes to once a year, the longer it lasts and the smaller the arc it backs up.
Two thousand years of explanations
The loop was the puzzle that moved the Earth.
For an Earth-centred sky, a planet that stops and backs up needs extra machinery. Ptolemy's Almagest, written in the second century, put each planet on a small circle, the epicycle, riding round a larger one, and the combined motion reproduced the loops well enough to predict them for centuries.
Copernicus's De revolutionibus (1543) gave the explanation used on this page: put the Sun in the middle and let Earth move, and the loops are what overtaking looks like. The texts behind that story are collected in Sources.
Retrograde motion, answered
Do planets actually move backward?
No. Every planet goes round the Sun in the same direction all the time. Retrograde motion is an effect of watching from Earth, which is moving too: when Earth overtakes an outer planet, or an inner planet overtakes Earth, the line of sight to the planet swings backward against the distant stars for a while.
Why does Mars go retrograde?
Earth is closer to the Sun and moves faster, so it laps Mars about every 780 days. For the weeks around the pass, Mars appears to drift backward against the stars. Its next retrograde runs from 10 Jan 2027 to 1 Apr 2027, 81 days, with opposition on 19 Feb 2027.
Why is Mars brightest during its retrograde?
Because the middle of the retrograde is when Earth passes Mars, and that is when the two are closest. At the 19 Feb 2027 opposition Mars is 0.68 AU from Earth, and it sits opposite the Sun, so it is up all night.
Why does a retrograde look like a loop?
Because the planet's orbit is tilted a little to Earth's. While the planet slows, backs up and moves on, its distance above or below the ecliptic also changes, so the path opens into a loop, flattens into a zigzag or bends into an S, depending on where in its tilted orbit the retrograde falls.
Which planet has the longest retrograde?
Among the retrogrades drawn on this page, Pluto's is the longest at 162 days and Mercury's the shortest at 20. The slower the planet, the longer it lingers: the outer planets spend months retrograde, Mercury about three weeks.
Do the Sun and the Moon go retrograde?
No. Seen from Earth, the Sun and the Moon always move eastward through the zodiac. Retrograde motion needs two bodies orbiting the Sun at different speeds, one watching the other, and the Moon orbits Earth itself.
Every position, date and speed on this page is computed from the ephemeris, in UTC.