Retrograde Tracker (行星逆行)

Is Mercury Retrograde? The Ephemeris Answers

Overview

No astrological question is asked more often, or answered more sloppily, than 'is Mercury retrograde?' The internet answers with memes; askTIAN answers with the ephemeris. A planet stations when its apparent longitude reverses — the moment its speed against the zodiac crosses zero — and the tracker computes those stations to the minute: every planet's current motion and speed, the upcoming stations across a configurable horizon, and for Mercury (or any planet you choose) the full window modern astrologers actually track — station-retrograde to station-direct, wrapped in the pre- and post-shadow zones where the planet walks the same degrees three times. The 2026 Mercury calendar this engine computes matches the published almanac dates exactly, station signs included, and those anchors are locked in the test suite.

Origin & history

Retrograde motion puzzled every geocentric astronomer and decorated every astrology since: the wandering stars periodically stop, back up, and resume — because Earth and planet overtake one another on their orbits, a geometry of viewpoints that heliocentrism dissolved and astrology kept as symbol. Mercury's three-to-four annual reversals became modern astrology's favorite scapegoat — the communication planet 'moving backward' through contracts, commutes and inboxes — and the practice grew its own refinements: the shadow zones (the degrees the planet crosses before and after the reversal, walked three times in total) and the station days themselves, held to be the sharpest moments of the cycle. The tracker computes all of it and labels the interpretive layer what it is: modern astrological convention around an apparent-motion fact.

The engineering follows the electional suite's standard set by the void-Moon endpoint: dense scanning on the shared Meeus ephemeris with bisection to the minute, external anchoring before shipping, and honesty about precision. The three 2026 Mercury retrogrades — February 26 to March 20 in Pisces, June 29 to July 23 in Cancer, October 24 to November 13 in Scorpio — reproduce the published Britannica and almanac dates exactly, and the test suite locks both the dates and the station signs. One disclosure matters near the edges: a stationing planet moves at a few arcseconds per day, so different tables can differ by hours on the exact station minute — the method string says so rather than implying false precision.

How it works

Give a UTC date. The tracker reports all eight planets' apparent motion (direct or retrograde), their speed in degrees per day, and their zodiac positions. For the focus planet — Mercury unless you choose another — it finds every station in the horizon by scanning the speed for sign changes and bisecting each crossing to the minute, then assembles the consumer window: the station-retrograde and station-direct moments with their sign positions, the retro zone between their degrees, the pre-shadow beginning when the still-direct planet first enters that zone, and the post-shadow ending when it finally re-passes the station-retrograde degree. The status field says where the date stands — before the window, pre-shadow, or retrograde — and the upcoming-stations list covers the horizon. Everything is deterministic, UTC, and reproducible.

Good for

Use cases

The Mercury Banner

One call powers 'Mercury is retrograde until Nov 13' — or 'pre-shadow began Oct 4' for the readers who track the zone — with dates that match every published calendar.

Astro-Weather Dashboard

Void-Moon windows and retrograde status on one scheduling surface — the two modern electional signals, both ephemeris-computed, both externally verified.

Retrograde Season Planner

The upcoming-stations list across 400 days renders a full retrograde calendar for any planet — content teams schedule the season's posts from one response.

Practitioner Detail

Station positions to the tenth of a degree let horary and electional workers see exactly which natal points a station sits on — the layer the meme sites never carry.

Key terms

Station
The moment a planet's apparent longitudinal speed crosses zero — station-retrograde begins the backward arc, station-direct ends it. Found by scan and bisection, to the minute, UTC.
Retrograde
Apparent backward motion against the zodiac — viewpoint geometry from overtaking orbits, kept by astrology as symbol and labelled convention here.
The Retro Zone
The degrees between the two stations — walked three times per cycle, forward, backward, forward.
Pre-Shadow
From the direct planet's first entry into the retro zone until station-retrograde — the approach practitioners begin watching.
Post-Shadow
From station-direct until the planet re-passes its station-retrograde degree — the cycle's true exit.
Station Days
The days around the zero crossing, when the planet barely moves — held by the practice to be the cycle's sharpest moments, and the hardest for tables to time (disclosed).
Calendar-Verified
The 2026 Mercury dates reproduce the published almanac calendars exactly, dates and signs, locked in the test suite.
Focus Planet
Mercury by default; any of the eight planets can take the detailed window — Venus and Mars retrogrades matter to practitioners too.

API

The askTIAN Retrograde API computes planetary stations from the shared ephemeris — all eight planets' current motion and speed, upcoming stations across up to 400 days, and the focus planet's full consumer window with both shadow zones by actual degree crossings — externally anchored (the three 2026 Mercury retrogrades match the published calendars exactly, dates and signs test-locked), with apparent-motion honesty and edge-precision disclosure in every response. Pure deterministic compute, no LLM, 2 TIAN. Pairs with moon.voidOfCourse as the modern astro-weather suite.

Endpoint: POST /trpc/retrograde.track — 2 TIAN Points. See the API documentation and Playground.