Reference · Astronomy
What is an ingress?
Kevin Blaxton — software builder; astrology student for 40+ years · figures computed by the OrbHeaven engine
Published · Last revised
An ingress is the moment a planet, the Sun or the Moon crosses from one zodiac sign into the next — the instant its apparent ecliptic longitude passes a sign boundary, a multiple of 30°. How often it happens depends only on how fast the body moves: the Moon changes sign every couple of days, the slow outer planets only once in many years.
What is an ingress?
It is a coordinate crossing. The zodiac is divided into twelve 30° signs, and a body is “in” whichever 30° slice of ecliptic longitude it currently occupies. When its longitude passes a boundary — 0°, 30°, 60°, and so on — it ingresses into the next sign. The four cardinal ingresses of the Sun (into Aries, Cancer, Libra and Capricorn, at 0°, 90°, 180° and 270°) are the equinoxes and solstices.
A verified example, from the engine
OrbHeaven finds an ingress by watching a body’s computed longitude cross a multiple of 30° and bisecting to the second. For example, after 1 January 2025 the Sun crossed from Capricorn into Aquarius — the 300° boundary — on 19 January 2025. A second before that instant the engine still places the Sun in Capricorn; at it and after, in Aquarius. The date and the degree are read from the same ephemeris the charts use, and the test suite re-derives them.
The figure shows the 360° circle of ecliptic longitude divided into the twelve signs; an ingress is simply the body’s longitude crossing one of those divisions.
How often each body ingresses
It follows from speed. The Moon moves about 13° a day and so ingresses roughly every two and a quarter days; the Sun about 1° a day, so once a month; Mars about every two months on average; Jupiter about once a year; Saturn about every two and a half years; and Pluto, slowest and on an eccentric orbit, only every eleven to thirty-two years.
That is why the Moon’s ingresses are a minor, frequent rhythm while the ingresses of the slow planets mark the turning of eras.
A short history
Tracking when a planet entered a new sign is among the oldest uses of astronomy: Babylonian astronomers tabulated the sign-entries of the Sun, Moon and planets, and Hellenistic astrology built the technique of the ingress chart — a chart cast for the Sun’s entry into Aries (the spring equinox), read in mundane astrology as a forecast of the year for a place. The crossings were watched and recorded long before any meaning was assigned to them.
What an ingress is read as
Interpretation, labelled as such: an ingress is read as a planet taking on the style of the sign it enters — a change of tone in how that planet acts. The slow-planet ingresses are treated as the big shifts of the collective mood, while the Moon’s frequent ingresses colour the texture of a day. The crossing itself is exact arithmetic; the meaning is tradition.
Common misconceptions
- Is an ingress a physical event?
- It is a coordinate crossing — a body’s ecliptic longitude passing a 30° sign boundary. Nothing happens to the body; it simply moves from one slice of the zodiac into the next.
- Why do some planets ingress so rarely?
- Because they move slowly. Pluto can take decades to cross a single sign, so its ingresses are rare, era-marking events, while the Moon ingresses every couple of days.
References & further reading
- [1] Meeus, J., Astronomical Algorithms, 2nd ed. (Willmann-Bell, 1998) — apparent longitude and the Sun’s cardinal ingresses (the seasons).
- [2] IAU / standard ephemerides — mean daily motion of the Moon and planets.
- [3] OrbHeaven engine (astronomy-engine) — the ingress instant from a longitude crossing; re-derived in ingress-demo.test.ts.
Suggested citation
Blaxton, K. (2026). What is an ingress. OrbHeaven Reference. https://orbheaven.com/reference/ingressesRevision history
- First build (concise). Reused degree-ruler figure; verified example (Sun into Aquarius, 300°, 19 Jan 2025) re-derived in ingress-demo.test.ts; rates by body and the seasonal cardinal ingresses; cross-links The Zodiac Signs, Transits and The Tropical Zodiac. No photo, no interactive.
About a minute. Birth time optional, and no account until after you have seen it.
More in the reference library
What are the twelve signs of the zodiac?
The twelve signs are equal 30° slices of the ecliptic, sorted by four elements and three modalities. This explains the structure, how a sign is determined, why the signs are not the constellations they are named for, and what the tradition reads into them.
What is a transit in astrology?
A transit is a planet’s ongoing motion meeting a point in your fixed birth chart. This explains how current positions are calculated, how a transit builds to exact and fades, and keeps the astronomy separate from the astrological reading.
What is the tropical zodiac, and why are the signs not the constellations?
The tropical zodiac measures the signs from the March equinox, not from the stars — which is why, after millennia of precession, the signs no longer line up with their constellations. With engine-computed tropical/sidereal/constellation comparisons.