The declared direct day-for-year rule
Secondary progression uses a symbolic correspondence: a day after birth represents a year of life. For the Atlas first method, symbolic age uses UT1 Julian dates: (targetJD − natalJD) ÷ 365.25 and progressedJD is natalJD + age. The 365.25-day year divisor is an Atlas convention that must travel with the result; it is not a claim that every practitioner or program uses that same elapsed-age key.
The calculator is direct only: the target must be at or after birth. It returns geocentric, apparent tropical planetary positions at the mapped epoch. The mapped epoch is an ephemeris date selected by the rule, not the person’s present astronomical sky.
Astrodienst: chart types and progression conventions ↗Astropy: Julian epoch and Julian year ↗
Worked arithmetic example
For synthetic inputs natalJD 2451512.5 and targetJD 2463200.5, elapsed time is 11,688 days. Dividing by 365.25 gives age 32 exactly. The direct progressed epoch is 2451512.5 + 32 = JD 2451544.5: 32 ephemeris days after the natal epoch. This verifies the time mapping only; it is not a claim about any individual or a validated forecast.
Retain the unrounded Julian day for the planetary calculation. A rounded displayed civil timestamp must not be converted back into the engine as though it were the original epoch.
Do not merge different direction methods
Secondary planetary progressions select positions from days after birth. A solar-arc direction instead applies a selected solar motion as an arc to chart factors. Primary directions concern diurnal geometry and require their own geometric definitions and time key. Results from these constructions are not interchangeable merely because each may be described as a direction or progression.
Houses and angles require a separately declared progression treatment. Astrodienst documents alternative approaches for progressed angles, so an ordinary chart calculated at the mapped epoch must not be silently presented as the default progressed-house method. The first Atlas planetary scope intentionally does not calculate progressed houses, Ascendant, Midheaven, or angle contacts.
Read a stated symbolic method as a stated symbolic method
Practitioner reading rules belong to named Western schools or authors. A calculated sign placement or longitude contact is a reproducible result under the displayed conventions; an interpretation is a further symbolic proposal. Compare it with lived experience without treating it as a necessary event, diagnosis, or causal explanation.
The workspace provides scoped planetary comparisons and selected source-linked reading material. It does not calculate exact sign-ingress dates, judge all possible progressed aspects, or supply an independent-engine parity claim. Exact ingress timing needs a separately specified crossing calculation and validation.
Word origin · etymology
The ordinary English words secondary and progression: secondary denotes a second order or stage, while progression denotes advancing or a connected sequence.
Merriam-Webster establishes those general English senses, not the historical naming of the astrological technique. Available method documentation distinguishes secondary progressions from primary directions and solar arcs, but it does not establish why this method acquired the label “secondary.” This entry therefore makes no founding-author, first-use, or derivation claim for the technical name.
Merriam-Webster Dictionary: secondary ↗Merriam-Webster Dictionary: progression ↗
How we know · epistemology
A stated symbolic time-mapping convention plus calculated ephemeris positions
The day-for-year correspondence is an adopted astrological analogy. Arithmetic can reproduce the mapped epoch under a named key, and an ephemeris can describe positions at that epoch; neither establishes that the mapping predicts events or personal traits.
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