What is computed, and what is not.

The stance

Astrology here is offered for reflection, contemplation, and entertainment only, and Charting Stars makes no claim of predictive accuracy (terms). The models below date and rank configurations of the sky. None of them says what will happen in a life.

When we say something is checked, we mean the astronomy: where a planet was, when it turned, when an eclipse happened. Those are compared with independent sources. What a configuration means is interpretation from the tradition, and nothing on this site tests it. Each section says which parts are computed, which are conventions chosen from the tradition, and which are words written about them.

The engine

Positions come from astronomia, an implementation of Meeus’s Astronomical Algorithms: VSOP87 for the Sun and Mercury through Neptune, Meeus’s lunar theory for the Moon, and Meeus’s Pluto series from 1885. Natal Pluto for births from 1801 to 1884 comes from a table of NASA JPL Horizons positions; there is no Pluto before 1801, and the Dial shows Pluto from 1885 to 2099. Chiron also comes from a JPL Horizons table: a point in birth charts from 1850 to 2100, and a moving body on the Dial. The zodiac is tropical; houses are whole-sign from the Rising sign; the Ascendant comes from sidereal time at the birthplace, with the birth time converted to Universal Time using the place’s own historical clock. Bodies are placed at Terrestrial Time, the uniform scale an ephemeris is a function of. From 1972, when Coordinated Universal Time began, that is the birth instant plus 32.184 seconds plus the leap seconds so far, exactly 69.184 seconds now, and the same 69.184 seconds for every later instant until another leap second is announced, as NASA JPL Horizons holds it (our copy of the IERS leap-second list is good until June 2027). Before 1972 a clock time is Universal Time and the Naval Observatory’s published ΔT is added instead, 13 seconds in 1800. A chart for a future date therefore carries no forecast of the Earth’s rotation; ΔT beyond the Naval Observatory’s data is a stated convention that only a birth before 1657 can reach. Sidereal time and so the Ascendant stay on the clock time read as Universal Time. The Moon gets nutation in longitude; the planets still leave out nutation and aberration (the Sun has both), and that is most of the small differences the checks below find for them. The live sky and the almanac have not moved to Terrestrial Time yet, so for the Moon a birth chart and the sky now can differ by up to about an arcminute. Delivered readings quote the engine’s degrees at the time they were written, and a fresh chart can differ by up to about a minute of arc after this release; no reading is regenerated.

How it is checked: seven Rodden-rated birth charts are cast in every build against published values, and their positions are frozen so that a change of more than 0.05° fails. Ten positions (seven Suns, plus Einstein’s Moon, Uranus and Neptune) agree with NASA JPL Horizons within 0.05°. A separate audit casts the Sun, Moon and planets at forty random instants from 1850 to 2100 (stated in Terrestrial Time, so the audit tests the ephemeris and not the Earth’s rotation) and requires the Sun within 1″ of JPL Horizons, the Moon within 10″ and each planet within 72″; Chiron and the early Pluto table are checked the same way at instants left out of their tables. Each of these is evidence for the cases checked, not a proof for every date, and the birth time is usually the larger uncertainty: four minutes moves the Rising degree by about one. The full pipeline is in how we calculate a birth chart, and the checks, sources and open data are in the birth chart calculation test set.

The almanac’s dates are compared in every build with saved answers from the US Naval Observatory and NASA JPL Horizons. Mercury’s and Venus’s turning points for 2026–27 fall within ten minutes of Horizons. New and full Moons, equinoxes and solstices come out up to two minutes later than the Naval Observatory’s times, mostly because the almanac still reads Universal Time as ephemeris time, about a minute off. The slow outer planets’ turning points can sit hours from Horizons, up to about seven for Pluto, because the almanac finds most of them without the small corrections for nutation and aberration. For those planets the date is the useful part, though for the slowest a time in the last several hours of the UTC day can belong to the next date.

Transits and the timeline

A transit is a moving planet in aspect to a point in a birth chart: a conjunction, sextile, square, trine or opposition, inside an orb. The orb depends on the moving body, tight for the slow planets because they stay in aspect for months. One table serves every contact on the site: the Dial’s bars, the tap text, the daily letter and the readings. The North Node is read by conjunction and opposition only.

The timeline finds each transit’s entering, exact and leaving moments across 1850–2100, from the engine’s daily samples interpolated within 0.0005°. A retrograde loop is one transit with one or several passes. Contacts between two planets are timed to within minutes for the Sun, Moon and inner planets and to within hours for the slow planets; contacts to the Rising sign or Midheaven are dated to the day, because they depend on the birth time. The method is written up in how we date a transit.

The headline over the free Dial is sign-level: the nearest ingress, station or new or full Moon, and the fastest planet in the same sign as your Sun, Moon or Rising or two, three, four or six signs away. It is shared by everyone with that placement. The reading of a transit on your own chart adds the house it falls in, the rulers, dignity and the lords of the time, and ranks transits by tightness of orb, times a weight for the planet, times a multiplier that starts at one and adds a half for each time-lord technique naming the planet, and another half when two or more name it. Only the bands the page draws count, with Zodiacal Releasing from the lot shown. Those overlaps come mostly from how long the periods run: in 2,000 simulated births (born at random times from 1900 to 1999, between 60°S and 60°N), the profection, Zodiacal Releasing from Spirit and the Vimshottari dasha all name the same planet in about 4 of every 62 adult years with their subdivisions drawn (about 1 with the main periods alone), Saturn most often. The reading’s Method line gives the figure for the techniques it names beside any overlap. The weights are set by hand, not fitted to anything:

Under every Dial, the echoes name the last and next time each slow planet passed through its current sign. Eclipses come from Meeus’s eclipse solution and are checked against NASA’s Five Millennium Canon from 1850 to 2100. The aspects the planets make to one another right now, with the wider orbs a chart’s own aspects use (conjunction 8°, sextile 4°, square 7°, trine 7°, opposition 8°, wider with the Sun or Moon), are in the aspects table on /sky-now.

Fixed stars and Algol

A short table holds 8 bright stars named in the tradition (Regulus, Algol, Spica, Aldebaran, Antares, Fomalhaut, Alcyone and Sirius), with positions for the year 2000 taken from astro.com’s fixed-star catalog. Each position is moved to the chart’s date for precession at a steady rate of about 50″ a year. When a planet on a celebrity chart, or the Sun’s degree on a birthday page, falls within 1° of a star’s longitude, the star is named with its magnitude and the nature the tradition gives it. The match is by longitude along the zodiac only: Algol sits 22° and Sirius about 40° from the ecliptic, so a contact does not mean the two were close in the sky. The nature is the tradition’s word, not something computed.

Algol also fades every 2 days, 20 hours and 49 minutes, when the fainter star of the pair passes in front of the brighter. The next fade on /sky-now comes from a timetable fitted to twenty eclipses measured by NASA’s TESS satellite in 2019, 2022 and 2024. Each of those years is predicted from the other two within 20 minutes, and the timetable is given to about 20 minutes through 2028. It does not say whether Algol is above your horizon or the sky is dark enough to see it, and it gives the fade no meaning.

Time-lord bands

Four timing techniques from three traditions, each computed from the birth data by a fixed rule and each a convention, not a measurement. Calculators disagree on some of them, so the convention is named.

• Annual profections. One sign per year of life from the Rising sign; the sign’s ruler is the lord of the year. The year turns at the solar return. Needs a birth time.
• Zodiacal Releasing from the Lots of Fortune and Spirit, after Valens, in 360-day years. Peak periods are the signs angular to the Lot of Fortune, for both lots. Needs a birth time.
• Vimshottari dasha from the Moon’s nakshatra in the sidereal zodiac (Lahiri ayanamsa, a straight-line approximation checked against its published 1956 definition), with years of 365.2425 days. Another ayanamsa moves every date, and so does the birth time: every date after birth moves together, by about five days a minute when the first period is Venus (near a nakshatra boundary the first lord can change, but the later dates still move together). The Vedic chart shows that window for each chart, split into birth time, the choice of Lahiri variant and the engine’s measured error.
• BaZi pillars. The four pillars, the annual pillar from Li Chun to Li Chun, and the ten-year luck pillars, which need the pillar direction. Civil time; no true-solar-time correction, and no favourable-element or clash analysis.

Turning points against ordinary days

On the celebrity timelines, each slow planet’s share of a life’s dated events in orb sits beside its share of the life’s ordinary days, with the chance of doing at least as well at random. The claim is only that every contact comes with the rate it has to beat; across all the lives the numbers sit near chance. The count of comparisons that look 1 in 20 is set beside what chance alone gives with so few events a life, which is no more than one in twenty of them, and beside the same count adjusted for every comparison at once. The page also states its limits: the events were chosen after the fact by people who knew the life, the ordinary days include childhood, when none of those events could happen, and the arithmetic treats events as independent although a slow planet’s contact lasts months.

Horoscopes

The sign horoscopes are sign-level. Computed from the day’s ephemeris: the Moon’s sign and its aspect to the sign, the heaviest planet in aspect to the sign, the planets that are retrograde, and the live positions. Chosen from fixed lists, varied by date: the wording, and the mood, lucky number and lucky colour, which are for fun and say so.

The personalized daily letter reads the day’s transits against your own chart: the tightest contacts inside the orb table above. The paid month-ahead section samples the next thirty days at noon and dates each slow-planet contact’s closest approach to the day, not to the minute.

Compatibility

The sign compatibility scores are Sun-sign only: a short table of classic pairings, and for every other pair the average of an element score and a modality score, with small fixed adjustments per category. They use no ruling planets, birth charts or live sky. Comparing two birth charts is what synastry does: every planet of one chart in aspect to every planet of the other, with house overlays. A composite chart takes the midpoint of each pair of planets and angles.

Readings

Written readings are drafted by a language model from the computed facts of your chart, with instructions to quote the values given and invent none. The prose is interpretation and is not validated. Forward-looking sections anchor the year on the techniques that have dates (the profection birthday, the solar return, releasing periods, the BaZi year and decade); the transits in a reading are the sky at the moment it was written, and the reading may not give a transit a future date. A reading’s own Dial is where transits are dated.

Corrections

If a number here, or anywhere on the site, disagrees with an ephemeris you trust, write to hello@chartingstars.com. More about the practice is on the about page.