Pluto Transits to Natal Sun: Not the Same as Pluto Square Pluto

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A Pluto transit to the natal Sun is a stretch of time in which moving Pluto reaches one of eight degrees measured from the Sun in a birth chart. It is easy to mix up with a different measurement that often falls in the same decade of life: Pluto reaching a square to its own natal position. This page dates both for one invented chart and shows why they stay separate.

Two kinds of statement are involved. Dates are calculated: given a natal Sun, a window and an ephemeris, anyone can list Pluto's exact crossings and check them. Meaning is interpretive: many astrologers read Pluto against the Sun as a time to reflect on direction and on what feels essential to who you are. "Transformation" is the usual word for that theme. It is an interpretive theme, not an event the dates predict and not something anyone is required to go through.

Educational guide: the site has no transit calculator, transit calendar or timing report, and the free birth chart produces the natal chart only. Everything below was worked out offline for a fictitious birth. For your own dates you need your natal Sun and a Tropical ephemeris.

How the chart calculates Pluto

Pluto is not handled like the other planets. Mercury to Neptune come from the VSOP87B planetary theory; Pluto comes from astronomia's version of the series in chapter 37 of Jean Meeus's Astronomical Algorithms. The chart takes that heliocentric position, referred to the J2000 equinox, precesses it to the date, subtracts the Earth's position with a light-time correction and then applies the same apparent-place corrections as the other planets. The chart shows Pluto for birth dates from 1 January 1885 to 31 December 2099 and leaves it out otherwise.

The repository's Pluto test compares this routine with the Swiss Ephemeris at 12:00 UT on every day from 25 December 1919 to 8 January 2061. In this run that was 51,516 days, the largest difference was 1.78 arc-seconds and the root mean square 0.58. Retrograde flags agreed on every day outside the half-hour windows around stations; one flip, on 12 December 1961, fell inside such a window, 1.1 minutes from the Swiss station. All 281 stations in that span paired one to one with Swiss stations, the worst 0.28 hours apart and the average 0.06 hours. A second daily scan, 1 January 1885 to 31 December 2099 (78,527 days, largest difference 3.43 arc-seconds), applies the same longitude limit and the retrograde check outside near-station windows, but does not pair stations. The test limits themselves, 0.05° and half an hour, are allowances, not measured errors. The half-hour limit applies to station times, not to the moment Pluto crosses a target.

Worked example: Edinburgh, 29 December 1974, 10:25

The birth is invented. The positions come from the code the free chart uses.

• Birth record: Edinburgh, 10:25 on 29 December 1974. Britain was on Greenwich Mean Time, so the birth was at 10:25 UT and the local date matched the UT date; zoneinfo shows UT+0 for every minute.
• Natal Sun: 7°19' Capricorn, 277.3269° unrounded (two decimals 277.33°; degree and minute 277.3167°).
• Natal Pluto: 9°12' Libra, 189.2046°, at the same recorded time. The Sun is 88.12° ahead of Pluto, so the chart has a natal Sun-Pluto square 1.88° from exact. That is a birth feature with no dates; see Sun square Pluto (natal).
• Code: commit 0cca75ca. The Sun comes from astronomia's apparent solar longitude, a compact solar theory; Pluto from the routine described above.
• Window: from the birth to 00:00 UT on 31 December 2060, a cutoff chosen for this example inside the 1920 to 2060 range where the Pluto and Sun checks overlap. It is not a limit of the method and not a statement about anyone's lifespan.
• Method: Pluto every six hours; crossings narrowed below thirty seconds, stations to about a minute, which is bookkeeping rather than accuracy. The years around each group of passes, back to 1920, were scanned so a group cut short by the window could be labelled. Dates are UT.

Results for the eight targets

The waning square began before the window: Pluto crossed 187.3269° on 16 October 1974, ten weeks before the birth, and again in April and August 1975. Its 1974 loop had turned back on 9 January 1974 at 186.8284°, 0.50° short of the degree, so that loop added nothing.

The waning sextile shows how close to a station a pair of passes can sit. Pluto turned retrograde on 8 February 1986 at 217.3628°, just 0.036° beyond the 217.3269° target, so the January and February 1986 crossings came only three weeks apart, one each side of the turn. Dates like these are the most fragile in the table, as the section on calculation models shows.

Pluto to your Sun is not Pluto to Pluto

Pluto square natal Pluto measures moving Pluto against natal Pluto. This page measures it against the natal Sun. Both natal points below were computed for the recorded 10:25 GMT:

Both sequences run through 2012, and in that year the passes even alternate: Sun on 1 January, Pluto's own square on 4 March and 19 May, Sun again on 9 August and 26 October, Pluto's square on 28 December. That shared year is a consequence of this chart's natal Sun-Pluto square, which puts the two targets 1.88° apart. It does not make them one measurement. The degrees differ, the dates differ, and in a chart without that natal square these two contacts would usually fall years apart. Neither contact implies the other.

Birth time, calculation models and precision

On 29 December 1974 the Sun moved from 6°52' to 7°54' Capricorn (276.8846° to 277.9031°) between the first and last local minute. The Sun never stations, so those two minutes bound it.

Three of the contacts change count across that day, each where a target meets the longitude of a Pluto station inside its possible range. By the site's routines, at about these local times:

• Conjunction: three passes before about 01:39, five from about 01:39 to about 14:40, three after.
• Waxing sextile: three passes before about 06:44, five after.
• Waning sextile: three passes before about 06:14, five from about 06:14 to about 11:16, three after.
• Waning square: two passes inside the window all day, the first pass always before the birth.

The recorded 10:25 is about 51 minutes before the nearest edge.

An independent Swiss Ephemeris comparison agrees on Pluto: natal Pluto within 0.2 arc-seconds and the relevant Pluto stations within 1.2. It does not agree as closely on the natal Sun. The Swiss value is 277.3203°, 24 arc-seconds (0.0067°) below the site's 277.3269°, which is about nine and a half minutes of the Sun's motion. With the Swiss Sun every edge above moves about nine minutes later (01:48, 14:50, 06:52, 06:23 and 11:25), and the counts at 10:25 are the same. Rerunning the crossings with Swiss values throughout gives the same seventeen passes, but eight of the UT dates move to a neighbouring day, by up to about 24 hours for the 1986 pair beside the station. The Swiss scan gives 13 March and 31 December 2011 and 10 August 2012 for three of the conjunction passes, 24 October and 16 December 2049 for two waxing-sextile passes, and 20 February 1986, 23 June 1987 and 11 August 1987 for three waning-sextile passes. Both sets are reported here: one comes from the site's calculation model and one from an independent reference. They differ because two calculation routines give slightly different results for the natal Sun, the site's compact apparent solar routine and the Swiss Ephemeris, although both give an apparent Tropical longitude. The 24 arc-second gap therefore limits precision: dates next to a slow station cannot be stated more finely than that difference allows.

The displayed degree has the same effect on a larger scale. The truncated 7°19' (277.3167°) moved crossings by up to about 36 hours and changed ten dates; the two-decimal 277.33° moved them by up to about 12 hours and changed four. No count changed in either case.

Direction and what feels essential: optional reflection

Begin with the Sun's sign and natal aspects; include its house only if the birth time is dependable. The prompts are there to use or ignore.

• Conjunction. Which aims still feel like your own, and which have you kept mainly out of habit?
• Squares. Pressure between an established role and something you would like to rebuild. What small change would you test first?
• Sextiles and trines. Often read as workable times for deliberate change, at whatever pace suits you.

None of these contacts points to a crisis, a loss, a death, a health problem or a struggle over power, and none requires anything of you. Pluto does not cause events. Other natal Sun-Pluto aspects: Sun conjunct Pluto (natal). Other slow cycles to the Sun: Neptune transits to natal Sun and Uranus transits to natal Sun.

Working out your own Sun dates

1. Read the Sun on the free birth chart and turn it into a longitude, with the minutes as sixtieths of a degree; the minutes shown are truncated.
2. Add the eight offsets, reducing below 360.
3. Choose a window and note from a Tropical ephemeris every exact Pluto crossing of each target, plus every Pluto station whose longitude falls inside a possible target range. Look past the window's ends and call a cut group clipped.
4. With an uncertain birth time, bound each target by the Sun at the start and end of the possible interval, then work out the stretch of birth time on each side of every station inside those bounds, as with the conjunction's three, five and three passes above.
5. Write dates beside a near station as approximate, and name the ephemeris you used.

The Sun is not part of the Pluto test. It has its own check against 52 fixture charts dated 1920 to 2066, each within 0.05°; this birth and every tabled date fall inside both checks. For Pluto to the Sun outside 1920 to 2060, use one outside ephemeris and one time standard for both bodies.

For the general procedure see how to read transits without a transit tool. Ask the Astrologist can talk through your natal Sun or Pluto dates you looked up yourself; it does not calculate transit dates.

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• Pluto Transits to Natal Venus
• Pluto Transits to Natal Mars
• Neptune Transits to Natal Mercury
• Uranus, Neptune and Pluto Transits Through the Houses
• Pluto in Libra
• Pluto Transits to Natal Mercury