How the dates are computed

Position. For each planet the site computes the apparent geocentric ecliptic longitude: where the planet appears from the centre of the Earth, corrected for light travel time and aberration, measured along the ecliptic from the true equinox of date. That is the tropical zodiac, and the same quantity JPL Horizons reports as ObsEcLon. Positions come from astronomy-engine 2.1.19, an open-source library built on VSOP87, with Pluto by numerical integration.

Stations. A planet is retrograde while that longitude decreases. The site samples the planet's daily motion, every 6 hours for Mercury and up to every 2 days for Uranus, Neptune and Pluto, and wherever the motion changes sign it bisects the interval down to the instant the planet stands still. Forward to backward is the station retrograde; backward to forward is the station direct.

Shadows. The pre-shadow begins when the planet, still moving forward, first reaches the longitude where it will later station direct. The post-shadow ends when, moving forward again, it returns to the longitude where it stationed retrograde. Both crossings are found the same way, by bisection.

Sign. The sign of a retrograde is the sign at the station-retrograde longitude, in 30° tropical signs. When a retrograde crosses a sign boundary, its degree range names both signs.

Every day. Pages recompute the ephemeris daily, so today's answer, the next station and the countdowns move with the sky. No retrograde date on the site is typed by hand: tables, calendar feeds, alerts and the data files all come from this one calculation.

On 15 Oct 2026 every station from 2020 to 2030 was compared with NASA JPL Horizons. The largest timing difference was 2.0 h; the largest difference in position, 16.1″ of arc. 197 of 201 stations fall on the same UTC date in both; the other 4 sit within 2.0 h of midnight UTC and are listed under the table.

Neptune station direct: this site 2022-12-04 00:20 UTC, Horizons 2022-12-03 23:13 UTC.
Neptune station retrograde: this site 2027-07-09 22:49 UTC, Horizons 2027-07-10 00:23 UTC.
Pluto station direct: this site 2023-10-11 00:58 UTC, Horizons 2023-10-10 23:54 UTC.
Pluto station retrograde: this site 2030-05-12 23:10 UTC, Horizons 2030-05-13 01:10 UTC.

How the comparison works: the site’s station instant comes from the method above. Horizons is asked for the planet’s apparent ecliptic longitude around it, and Horizons’ station is the turning point of a parabola fitted to those samples. Near a station the slow outer planets move only arcseconds a day, so their station instant is soft by nature: sources that agree on the position can still differ by hours, and now and then by a calendar day. The check is the script verify:horizons in the site’s source, re-run whenever the calculation changes.

Times are UTC. Dates on the site are UTC calendar days. Mercury's next station retrograde is at 07:15 UTC on 24 Oct 2026; far enough east or west of Greenwich, that instant falls on a neighbouring date.

Tropical zodiac. Signs are measured from the equinox, as in Western astrology. Sidereal (Vedic) placements sit about 24° earlier, so the same retrograde can carry a different sign there.

Astronomy and meaning. Retrograde is an effect of the line of sight: Earth overtakes, or is overtaken by, another planet. The dates are astronomy; the meanings on the site are astrological tradition, offered for entertainment.

Before ephemerides. How people watched and computed the stations before modern tables, from Babylonian tablets on, is collected in 44 checked sources.

Times UTC; longitudes in degrees, apparent geocentric, ecliptic of date.