Pluto Transits to Natal Mercury: Two Kinds of Retrograde

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A Pluto transit to natal Mercury is the stretch of time in which moving Pluto reaches one of eight longitudes measured from Mercury in a birth chart. The longitudes and dates are arithmetic. What anyone makes of them is a separate, optional step: many astrologers treat Pluto against Mercury as a prompt to think about how you study things, which questions you keep returning to and how you put ideas into words. "Transformation" is the stock word for the theme. Here it stays a word for a theme, not a forecast.

This page has a narrow teaching job. Charts often mark Mercury with an R, and Pluto contacts often come in groups of three or five passes. The two facts look related, and they are not. The R describes Mercury's motion on the birth day. The repeated passes come from Pluto's own loops decades later. The example below keeps them apart.

Educational guide: Astrologist.com has no transit calculator, transit calendar or timing report, and the free birth chart works out natal positions only. The dates below were computed offline for an invented person. Your own dates need your natal Mercury and a Tropical ephemeris.

Targets, branches and a fixed degree

Add 0°, 60°, 90°, 120°, 180°, 240°, 270° and 300° to natal Mercury and reduce each sum below 360°. That gives the conjunction, a waxing and a waning sextile, two squares, two trines and the opposition. Waxing points lie up to 180° ahead of Mercury in zodiac order; waning points lie further round. Each is a separate target and is crossed on its own dates.

The target is the natal degree, fixed for life. Natal Mercury's direction at birth does not move it afterwards, and Mercury's later positions play no part. Only Pluto moves. Because Pluto's pace through the signs is very uneven, which targets it reaches in a window, and how many times, has to be found by scanning Pluto's dated path rather than estimated from an average speed.

Worked example: Bath, 8 April 1978, 14:20

The person is invented; the positions come from the code behind the free chart.

• Birth record: Bath, 14:20 on 8 April 1978, a recorded time treated as reliable. British Summer Time had begun on 19 March 1978, so the clocks were one hour ahead of UT and the birth fell at 13:20 UT. zoneinfo gives UT+1 for every minute of that date.
• Natal Mercury: 23°40' Aries, retrograde. At full precision it is 23.67173°; the chart's calculation output rounds that to 23.67°, and 23°40' read back as a number is 23.6667°. The dated table uses the full-precision value, and its degree-and-minute labels are shorthand. On the birth day it was moving backward at about 0.643° a day. Mercury had turned retrograde around 1 April 1978 near 26°07' Aries and turned direct around 25 April near 14°51' Aries (an hourly scan, so these two dates are approximate).
• Natal Pluto: 15°14' Libra (195.2373°), also retrograde. Mercury and Pluto are 171.57° apart. That is 8.43° from an exact opposition, just outside the natal calculator's fixed 8° orb, so the chart shows no natal Mercury-Pluto opposition. Natal aspects belong to the birth chart and have no dates; the transit opposition below is a different measurement.
• Code: commit fc9ebda6. Mercury comes from astronomia's VSOP87B theory through the chart's planetary routine. Pluto comes from the chart's own routine for Pluto, the series in chapter 37 of Meeus's Astronomical Algorithms, precessed to the date, reduced to the Earth with light-time and given the same apparent-place corrections as the planets; it is not a VSOP series.
• Window: from the birth to 00:00 UT on 31 December 2060. The cutoff is a choice for this example, inside the 1920 to 2060 span where the Mercury and Pluto checks overlap. It says nothing about anyone's lifespan.
• Method: Pluto sampled every six hours, crossings narrowed to under thirty seconds and stations to about a minute. That is bookkeeping, not a claim of accuracy. Each group was also scanned on both sides, back to 1920, so that a group cut by the window would be labelled clipped. Dates are UT.

The eight targets in this window

No group is clipped: every group of passes starts and ends inside the window, and none had a pass before the birth.

Two retrogrades that are easy to confuse

Mercury's retrograde is a birth fact. In April 1978 Mercury ran backward for about three and a half weeks, and the birth fell in the middle of that run. The chart's R records the direction Mercury was moving at 13:20 UT. It has no influence on how often Pluto later meets 23°40' Aries plus an offset. A direct Mercury at exactly the same degree would have produced exactly the same dates.

Pluto's loops make the repeated passes. Each year Pluto spends roughly five months moving backward. When a target sits inside one of those backward arcs, Pluto crosses it going forward, again going backward, and once more going forward: three passes. The opposition group shows this. Pluto turned retrograde on 26 January 1981 at 24°21' Libra, beyond the 23°40' target, then direct on 1 July 1981 at 21°31' Libra, short of it, so the target was crossed forward in December 1980, backward in March 1981 and forward in October 1981.

Five passes need two loops. The waning sextile target, 323.67173°, is caught by two neighbouring backward arcs. Pluto turned retrograde on 25 May 2038 at 24°15' Aquarius and direct on 4 November 2038 at 21°55' Aquarius, crossing the target three times, and then turned retrograde again on 26 May 2039 at 25°42' Aquarius and direct on 6 November 2039 at 323.3860°, about 0.2858° short of the target, so it crossed back once more and forward a final time. With the target exactly at that turning longitude, Pluto would touch it at the station without crossing it: three crossings plus a touch. Any lower, and the second loop turns before reaching it, for three crossings in all.

Birth time with Mercury moving backward

Mercury's backward motion has one practical consequence for the dates, and it runs the opposite way from most charts. A later birth time gives a slightly lower natal Mercury, not a higher one:

With the target lower, Pluto reaches it slightly sooner on its forward passes and slightly later on its backward ones. One hour later moved the opposition dates by about 24 hours earlier, 26 hours later and 16 hours earlier respectively. One hour earlier moved them by about the same amounts the other way. For the waning sextile the shifts reached about 45 hours, because Pluto creeps near its turning points. For a direct Mercury the signs would be reversed. Neither is a rule of thumb: the size of each shift depends on how fast Pluto happens to be moving at that crossing.

The recorded time is not doubted here, but it is worth knowing how far it could move before anything changes. Across the whole local birth date Mercury ran from 24.0453° at 00:00 to 23.4085° at 23:59, and every count in the table stays the same over that range. The waning sextile's five passes would only drop to three if natal Mercury were more than about 0.2858° lower than its full-precision value. Mercury falls to that value, 23.3860°, at about 00:48 local time on 9 April, outside the birth date; a birth at that moment would give the touch described above.

Rounding moves Mercury far less than an hour of birth time does, but not by nothing. Rerunning the scan with 23.67° changed no count and moved crossings by up to 2.8 hours; with 23.6667°, the value 23°40' gives, no count changed either but crossings moved by up to 8.3 hours, most near Pluto's turns. The second waning trine pass moves from 25 to 26 May 2005 with either value, and with 23.6667° the first waning square pass moves from 9 to 8 February 2020. The margin at the 2039 station shrinks from 0.2858° to 0.2807°, so the five passes stand.

Ideas, attention and inquiry: optional reflection

Begin with Mercury's sign and natal aspects; bring in its house only if the birth time is reliable. These prompts are optional.

• Opposition. Whose way of thinking or speaking do you find yourself answering most often, and what do you learn about your own position when you put it beside theirs?
• Squares. A friction between the way you like to study a question and what your current commitments allow. Which one habit of research or writing would you change if you could change only one?
• Trines and sextiles. Often read as workable times to take up a demanding subject, to edit something thoroughly or to have a frank conversation at your own pace.

These contacts do not reveal secrets, uncover hidden facts, signal deception, measure intelligence or point to any mental-health condition, obsession or trauma. They do not predict news, a diagnosis or the outcome of any conversation. Pluto does not cause anything, and a square is not a sign that something is wrong. For natal Mercury-Pluto contacts see Mercury conjunct Pluto (natal) and Mercury opposite Pluto (natal).

Finding your own Mercury contacts

1. Read Mercury from the free birth chart and turn it into a longitude, adding the minutes as sixtieths. The minutes shown are truncated; if a result sits close to a Pluto station, redo it with a more precise value.
2. Add the eight offsets and reduce below 360.
3. Pick a window. From a Tropical ephemeris, list every exact Pluto crossing of each target and every Pluto station whose longitude falls inside a possible target range. Look past both ends of the window so a cut group can be labelled clipped.
4. If the birth time is uncertain, find the whole range Mercury covered during the possible interval: its values at the start and end, plus any Mercury station inside the interval, because a station is an extreme in its own right. Mercury stations several times a year. Then check every Pluto station inside each target range and work out the stretch of birth times on each side of it.

The repository checks each body separately against the Swiss Ephemeris. Pluto is compared at 12:00 UT on every day from 25 December 1919 to 8 January 2061 (51,516 days); in the run for this batch the largest difference was 1.78 arc-seconds and the root mean square 0.58, and all 281 stations paired, the worst 0.28 hours apart. A wider 1885 to 2099 scan checks longitudes and retrograde flags without pairing stations. Mercury has its own daily check over the same 1920 to 2060 span (largest difference 3.50 arc-seconds, 888 stations paired). The test limits are allowances, not the error on any date above. For this chart an independent Swiss Ephemeris run put natal Mercury within 0.07 arc-seconds of the site's value, and at every crossing in the table Swiss Pluto sat within 1 arc-second of the target, whether the target was built from the site's full-precision Mercury or from the Swiss one, which moves no crossing by more than about 0.4 hours. Outside 1920 to 2060, take both bodies from a single outside ephemeris.

For the general workflow see how to read transits without a transit tool, and for Mercury's own retrograde periods how to see retrograde on your chart. Ask the Astrologist can talk through your natal Mercury or Pluto dates you have looked up; it does not calculate transit dates.

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• Uranus, Neptune and Pluto Transits Through the Houses