Natal Chart
A scientifically accurate mirror for self-reflection · natal charts, synastry and the Birth Explorer, checked against the Swiss Ephemeris
⚠ Before You Begin — Please Read Carefully
Astrology is a tool for self-reflection and symbolic exploration — not a predictive science, a diagnostic instrument, or a substitute for professional advice of any kind.
By using this calculator, you acknowledge and understand the following:
1. Self-Reflection, Not Prediction. The patterns described in a natal chart are symbolic frameworks drawn from a 2,000+ year interpretive tradition. They describe archetypal tendencies and themes for contemplation — they do not predict specific events, control outcomes, or determine your destiny. You always have full agency over your choices.
2. Not Professional Advice. Nothing generated by this application constitutes medical, psychological, psychiatric, financial, legal, or any other form of professional advice. Health themes are drawn from the medical astrology tradition and describe symbolic tendencies, not clinical diagnoses. Always consult qualified professionals for health, mental health, and life decisions.
3. Mental Health Awareness. Deep engagement with symbolic systems can occasionally trigger anxiety, obsessive checking, magical thinking, or distorted self-perception — especially in individuals prone to OCD, psychosis, or depersonalization. If you experience any of the following, please stop and consider speaking with a mental health professional:
• Feeling that the chart is controlling your life rather than offering reflection
• Difficulty distinguishing symbolic interpretation from literal reality
• Making major decisions based solely on astrological timing
• Feeling unable to stop checking planetary transits or positions
• Using astrology to avoid personal responsibility or justify harmful behavior
4. Astronomically Accurate, Symbolically Used. Positions of the planets, Moon, nodes and asteroids agree with the Swiss Ephemeris to within about one arcminute — but astronomical accuracy does not make astrological interpretation a science. A symbol system can resonate whether or not the placements are real; the value here is reflection, never mechanism. These positions are not meant for navigation or scientific work.
5. Not an Excuse. Your chart describes tendencies, not mandates. "My Mars is in Aries" is not an explanation for harmful behavior — it is an invitation to understand your energy and channel it consciously. Astrology at its best cultivates self-awareness, compassion, and growth. At its worst, it becomes a cage of self-fulfilling prophecy. Use it wisely.
🧘 Grounding Exercise — Before You Explore
Before generating your chart, take 30 seconds to ground yourself in the present moment.
Feet on the Floor: Press your feet firmly into the ground. Feel the solidity beneath you. Notice the weight of your body in the chair.
Three Breaths: Breathe in slowly for 4 counts. Hold for 4 counts. Breathe out for 4 counts. Repeat two more times.
Anchor Statement: Say to yourself (silently or aloud): "I am here, in this body, in this room. What I am about to explore is a symbolic framework for self-reflection. It does not control me. I have full agency over my life."
📋 Quick Verification — What Did You Just Agree To?
Please answer these questions to confirm your understanding. You must answer all correctly to proceed.
✦ For anyone who doesn’t know exactly when or where they were born
Records get lost or changed. Adoption, foster care, migration, or simply being born somewhere no one wrote it down can leave the most basic details uncertain. This page is for you.
Honest first: nothing in the sky records your birth, so this page can’t discover your birth time or place. What it can do is lay out every possibility that fits what you do know — which parts of your chart are the same in all of them, which depend on the missing details, and how the sky turned across those hours and places. Treat anything here as a possibility to reflect on, never as your confirmed birth details.
1 · What do you know?
Rough is fine. If a registered birthday might not be the real one, widen the range.
to
Memories like “at dawn”, “before the morning prayer” or “just after midnight” can go here.
Without a place, day/night and clock times can’t be applied — at every moment it is day somewhere on Earth.
Within of the point you tap on the globe
Rising sign at each place
Drag to spin · scroll or +/− to zoom · tap to choose a place. The bright spot is where the Sun is overhead; the shaded side is night.
Time Travel turns the globe: every moment shows which sign was rising where, and where it was day or night.
2 · Try one possibility as a chart
Open any single moment as a full chart on the natal page, to read it and see what resonates. It will be clearly marked as a possibility, not your birth details.
Uses the place chosen above (local time there). With no place, the time is read as UTC and the chart has no houses.
Finding your birth details
The sky can show possibilities; people and records hold the answers. Depending on where and how you were born, some of these may help — and if none of them exist for you, you are far from alone. Many people around the world were born at home, in a village, or somewhere no record was kept, and know their birthday only from what family remembers.
- Family and community memory. Parents, relatives, elders, neighbours, or the midwife or birth attendant who was there. Ask about anchors rather than clock times: the season or weather, a harvest, festival or religious holiday, a well-known event that year, the time of day (“at first light”, “after the evening meal”) or the Moon (“a full moon night”). This page can check those against the sky.
- Religious and community records. Baptism, christening or naming-ceremony records, and church, temple, mosque or village registers sometimes noted a date when nothing else did.
- Civil registration. National or local registry offices. Births are sometimes registered late, so a registered date can be the day of registration rather than the day of birth — worth keeping in mind.
- Medical records, where they exist. Hospital or clinic files, midwife notes, vaccination cards or early health booklets.
- Adoption, foster-care and children’s-home records. Agencies, courts and care organisations may hold files. In some countries and US states, adults who were adopted can request their original birth certificate or non-identifying information about their birth.
- School and early identity documents. First school enrolment, early passports or travel papers.
- DNA testing. It can connect you with biological relatives who may know your story. Consider cost, whether it’s available where you live, privacy, and your own readiness first.
- People who’ve walked this path. Groups led by adoptees and people who grew up in care can offer practical guidance and understanding.
Searching for where you come from can stir up a lot. Go at your own pace and lean on people you trust. Whatever you find or don’t find, what you already know about yourself counts.
Synastry is one of astrology’s core techniques: it lays two birth charts side by side to show the archetypal patterns between them — where energies harmonize, where they create friction, and what each person may draw out in the other. It describes potential relationship dynamics, not the outcome of a relationship.
Person 1
Person 2
✦ Discernment is the key
These patterns are archetypal potentials, not certainties. What makes synastry useful is your discernment: hold each description up against your lived experience of this relationship, and reflect honestly on what you notice in yourself and in the other person. Keep what genuinely rings true, set aside what doesn’t, and let the chart prompt conversation and self-reflection rather than replace them.
· Transit aspect lines to:
Time Travel visualizes orbits and aspects between the sky and both charts — a lens for reflection, not a forecast.
Aspect orbs: 6° for conjunctions, oppositions, squares and trines; 4.5° for sextiles — the same results as Astro-Seek’s synastry chart in testing. Other programs use other orbs, so an aspect near the limit may appear in one and not another.
🌍 Mundane Chart Lookup
Search for any country, US state, world city, California county or city to auto-fill its founding date, time, and coordinates into the natal chart form. This enables mundane astrology — the chart of a nation, city, or institution.
Selecting a location auto-fills the natal chart form with its founding date, time, coordinates, and UTC offset.
Your Natal Chart
│
Birth Location
Adds Ascendant, Midheaven, house cusps, and location-specific calculations.
Search 32,800 cities and towns worldwide (population 15,000+ plus all capitals) to fill coordinates and time zone automatically. Born somewhere smaller? Pick the nearest town, or enter exact latitude & longitude below.
│
▸ 📋 Saved Profiles & Locations
📋 Saved Profiles
No saved profiles yet. Fill in birth data below and save.
Click a profile chip to load it into the active form, or use the reference # for quick loading.
💾 Back up to your computer. Your profiles are stored only in this browser. Save a backup file so they survive clearing your browsing data, then restore it here anytime — on this or any device. You can also download a blank template to add people by hand in a spreadsheet.
📍 Saved Locations
No saved locations yet.
Save frequently used coordinates. Click to load into the active form.
✦ Exploring a possibility. This chart was opened from the Birth Explorer. It is one possible birth time and place — not confirmed birth details. Read it for what resonates, and compare it with other possibilities. Back to the Birth Explorer →
✦ A Tool for Self-Reflection ✦
This calculator shows you the sky exactly as it was at your moment of birth — a mirror for reflection, never a forecast. It makes no predictions and names no fixed fate. Even though there is a “Time Travel” area, this is to visualize orbits and aspects, not to see the future. Notice your own patterns, take what resonates, leave the rest, and stay the author of your own story.
▸ Overlay on Your astro.com Chart — work in progress, kinda crap at the moment
⚠ Work in progress — kinda crap at the moment. Alignment can be finicky.Upload your chart image from astro.com (or any wheel with the Ascendant on the left). Your image stays exactly as it is — this simply lays invisible, clickable points over it, computed from the chart you just calculated, so you can tap any body for the same reading. You line it up once by marking the wheel's center and outer edge.
astro.com nudges crowded glyphs apart to keep them legible, so in dense clusters a point lands at the exact degree on the ring rather than on the shifted glyph. Keep “spread crowded points” on to fan those out with leader lines.
astro.com nudges crowded glyphs apart to keep them legible, so in dense clusters a point lands at the exact degree on the ring rather than on the shifted glyph. Keep “spread crowded points” on to fan those out with leader lines.
Choose what to include
The report prints in black on white to save ink. Pick any extras you'd like added to the basics.
Basics
Add if you'd like
▸ Bodies & Precision
The Sun, Moon, and planets are computed with astronomy-engine — a JPL Horizons-validated implementation of VSOP87/ELP2000 — and agree with the Swiss Ephemeris to within about a third of an arcminute. The lunar nodes use the true (osculating) node. Chiron, Ceres, Pallas, Juno, Vesta, Pholus, Eris, Sedna and 48 further asteroids, centaurs and trans-Neptunian objects use orbit tables built from the Swiss Ephemeris asteroid files, matching it to within about one arcminute from 1800 to 2200. Black Moon Lilith is the mean lunar apogee. The main chart shows the Core Chart: the ten planets, the lunar nodes, Chiron, Black Moon Lilith, the four classical asteroids (Ceres, Pallas, Juno, Vesta), the distant bodies Eris and Sedna, and six more of the larger, long-known main-belt asteroids (Hygiea, Psyche, Fortuna, Nemesis, Lachesis, Minerva). Nearly 19,000 further asteroids can be added by number or name in Extended Chart Options, beneath the chart wheel.
The Extended Chart groups everything else — the smaller named asteroids, five centaurs, the trans-Neptunian objects, the calculated points, and the fixed stars. Only bodies whose positions are verified against the Swiss Ephemeris are included, and you can pick which of them appear in Extended Chart Options. It is kept for those who wish to keep the observational side of astrology alive, but it is held back from the main chart on purpose.
The Extended Chart is now folded in. A word of honesty: with this many bodies and aspect types, the chart generates hundreds of "exact" hits by pure chance — the multiple-comparisons problem. Treat these placements as an evocative exhibit, not as added signal. Click again to return to the Core Chart.
▸ Extended Chart — Additional Asteroids, Points & Stars
Expand your chart with 38 additional asteroids and trans-Neptunian objects, five centaurs, calculated points (Part of Fortune, Vertex, Mean Node, prenatal solar and lunar eclipses), nine fixed stars and the Galactic Center. Select categories or individual bodies below, then click "Calculate Extended Bodies" to add them to your reading. Only bodies with verified positions are offered: every asteroid and trans-Neptunian object here is computed from the Swiss Ephemeris asteroid files, and together with the points and stars all match astro.com to within 1′.
The named groups follow the myths behind the bodies’ names; your library does not interpret most of these bodies, so their pop-ups give the facts only.
🧘 Grounding Reminder
This quiz tests your understanding of your own chart. Remember: these are symbolic patterns for self-reflection. If any question triggers strong emotions, use the STOP skill — Stop, Take a step back, Observe, and Proceed mindfully. There are no wrong answers in self-understanding, only in the quiz.
▾ Chart Wheel
▾ Time Travel
—
startend
Tap any planet, sign, or angle on the wheel to learn what it represents.
▾ Aspect & Distribution Grids
▸ ⊕ Extended Chart Options & Add Asteroids — asteroid entry is a work in progress
➕ Add asteroids or special points — work in progress
⚠ Work in progress — this feature is still being developed. If something doesn’t look right, please compare against your astro.com chart.
Type one or more asteroid numbers or names, separated by commas — for example 42, 433, Isis. Special points use Swiss Ephemeris codes: h13 osculating Lilith, h21 interpolated Lilith, h22 Priapus, h40–h54 Uranian and hypothetical points. Nearly 19,000 asteroids are available, each checked against the Swiss Ephemeris to within 1′. Each body’s data loads from the site the first time you add it, so this needs an internet connection; your additions are remembered on this device.
Press Enter to add · Shift+Enter for a new line
Your core chart already carries the ten planets, both lunar nodes, Chiron, Black Moon Lilith, the four classical asteroids, the distant bodies Eris and Sedna, and six larger main-belt asteroids (Hygiea, Psyche, Fortuna, Nemesis, Lachesis, Minerva). Fold in additional bodies by category below, then refresh to plot them on the wheel, grids, and tables. A word of honesty: with this many bodies, aspects multiply by chance (the multiple-comparisons problem) — treat the extended set as an evocative exhibit, not added signal.
Your theme lists · from your reference workbook
Tick a list to fold in every body in it that has position data. The one-button fold-in above still adds only the original Extended Chart. Bodies without position data are listed under “list” and in the Glossary.
▸ ☉ Today's Sky & Your Potential
▸ Planetary Positions
▸ Chart Angles & Moon Phase
▸ Houses
▸ Aspects
▸ Chart Patterns
♡ Chart Comparison (Synastry) — open the synastry page →
Everything on this page is offered as a tool for self-reflection within the astrological tradition. None of it is medical, psychological, psychiatric, or other professional advice. The body correspondences in Rulerships come from the symbolic tradition of medical astrology and should never replace qualified healthcare. Challenging placements and aspects describe potential themes and sensitivities — not fixed destiny.
▸ Astrological Glossary — Interactive Reference
▸ Sources & Research — Your Library and the Data Behind the Chart
How the sources are used: every interpretive reading in this app is drawn from the books in your library listed below, or from a few web articles and a reference workbook you supplied (each marked as such), and a source line under each reading gives the book or article and its pages, chapter or date; where the source has a website, an author page or a publisher page, its title links there (↗). Where your library does not interpret something — a newly discovered body, a modern system such as the Destiny Matrix — the app gives the facts and says so. The astronomy and data sources compute positions, times and places; they make no astrological claims. Astrology is a symbolic and interpretive tradition, not an empirical science, so read every source with discernment. The DBT skills that appear beside some readings come from Marsha Linehan’s Dialectical Behavior Therapy, a skills framework rather than an astrological source.
▸ Destiny Matrix — Tarot Numerology of Your Birth Date
▸ Symbol Reference — Every Glyph Explained
▸ Rulerships — What the Planets & Signs Govern
Rulership ties each planet and sign to things held to share its nature. The entries below are taken from Rex E. Bills’s The Rulership Book, a directory of astrological correspondences, with each planet’s keywords and the sign–body table from Margaret Hone’s The Modern Text-Book of Astrology. Bills himself warns that there is wide disagreement on many rulerships — specific stones, colours, trees and herbs especially — and that many lists have simply been copied since ancient times; Hone strongly cautions against using the body correspondences in more than broad outline.
The Planets & What They Rule
☉ Sun · rules Leo
Keywords (Hone): power, vitality, self-expression
Body: heart, spine • Metal: gold • Day: Sunday • Colours: full spectromatic tones
People: kings, royalty, leaders, those in authority
Places: palaces, theaters
Body: heart, spine • Metal: gold • Day: Sunday • Colours: full spectromatic tones
People: kings, royalty, leaders, those in authority
Places: palaces, theaters
☽ Moon · rules Cancer
Keywords (Hone): response, fluctuation
Body: breasts, stomach • Metal: silver • Day: Monday • Colours: iridescent and opalescent hues
People: the common people, one’s mother, nurses
Places: the sea, harbors, kitchens, wells
Body: breasts, stomach • Metal: silver • Day: Monday • Colours: iridescent and opalescent hues
People: the common people, one’s mother, nurses
Places: the sea, harbors, kitchens, wells
☿ Mercury · rules Gemini & Virgo
Keywords (Hone): communication (mentally and by transport)
Body: nervous system, hands, organs of speech • Metal: mercury • Day: Wednesday • Colours: dark indefinite colors
People: writers, merchants, messengers, students, clerks
Places: schools, post offices
Body: nervous system, hands, organs of speech • Metal: mercury • Day: Wednesday • Colours: dark indefinite colors
People: writers, merchants, messengers, students, clerks
Places: schools, post offices
♀ Venus · rules Taurus & Libra
Keywords (Hone): harmony, unison, relatedness
Body: throat, kidneys, ovaries, complexion • Metal: copper • Day: Friday • Colours: pastel tints
People: artists of all kinds, lovers, opera singers
Places: gardens, bedrooms, beauty parlors
Body: throat, kidneys, ovaries, complexion • Metal: copper • Day: Friday • Colours: pastel tints
People: artists of all kinds, lovers, opera singers
Places: gardens, bedrooms, beauty parlors
♂ Mars · rules Aries (and, traditionally, Scorpio)
Keywords (Hone): energy, heat, activation
Body: head, muscles, adrenal glands • Metal: iron, steel • Day: Tuesday • Colours: flaming and somewhat discordant hues
People: soldiers, athletes, butchers, mechanics
Places: forges, foundries
Body: head, muscles, adrenal glands • Metal: iron, steel • Day: Tuesday • Colours: flaming and somewhat discordant hues
People: soldiers, athletes, butchers, mechanics
Places: forges, foundries
♃ Jupiter · rules Sagittarius (and, traditionally, Pisces)
Keywords (Hone): expansion, preservation
Body: liver, thighs • Metal: tin • Day: Thursday • Colours: rich, full hues
People: judges, priests, professors, bankers
Places: courts of law, temples, universities
Body: liver, thighs • Metal: tin • Day: Thursday • Colours: rich, full hues
People: judges, priests, professors, bankers
Places: courts of law, temples, universities
♄ Saturn · rules Capricorn (and, traditionally, Aquarius)
Keywords (Hone): limitation, cold
Body: bones, teeth, joints • Metal: lead • Day: Saturday • Colours: lifeless, flat or dark values
People: farmers, coal miners, old people
Places: mountains, ruins, prisons
Body: bones, teeth, joints • Metal: lead • Day: Saturday • Colours: lifeless, flat or dark values
People: farmers, coal miners, old people
Places: mountains, ruins, prisons
♅ Uranus · rules Aquarius (modern)
Keywords (Hone): change — revolutionary, disruptive, dictatorial
Body: ankles, calves, electricity in the body • Metal: uranium • Colours: electric, mixed, changeable colors
People: inventors, astrologers, aviators, eccentric persons
Body: ankles, calves, electricity in the body • Metal: uranium • Colours: electric, mixed, changeable colors
People: inventors, astrologers, aviators, eccentric persons
♆ Neptune · rules Pisces (modern)
Keywords (Hone): nebulousness, impressionability
Body: feet, pineal gland • Metal: neptunium • Colours: deep values or white
People: mystics, dreamers, healers, addicts
Places: oceans, hospitals, cinemas
Body: feet, pineal gland • Metal: neptunium • Colours: deep values or white
People: mystics, dreamers, healers, addicts
Places: oceans, hospitals, cinemas
♇ Pluto · rules Scorpio (modern)
Keywords (Hone): elimination, renewal, regeneration
Body: reproductive organs, organs of elimination • Metal: plutonium • Colours: murky, angry and luminous shades
People: detectives, gangsters
Places: the underworld, sewers
Body: reproductive organs, organs of elimination • Metal: plutonium • Colours: murky, angry and luminous shades
People: detectives, gangsters
Places: the underworld, sewers
The Signs & the Body
Hone’s table of the part of the body and the bodily system linked with each sign, from head (Aries) to feet (Pisces) — the scheme medieval writers drew as the “Zodiac Man” (Wedeck):
♈Ariesthe head
♉Taurusthe throat
♊Geminithe hands, arms and lungs; the nervous system
♋Cancerthe breasts and stomach; the alimentary system
♌Leothe heart and back; the cardiac system
♍Virgothe intestines; the alimentary system
♎Librathe kidneys
♏Scorpiothe sexual organs; the generative system
♐Sagittariusthe hips, thighs and liver; the hepatic system
♑Capricornthe knees; the bony system
♒Aquariusthe calves and ankles; the circulatory system
♓Piscesthe feet; the lymphatic system
Which Planet Rules Which Sign
Hone: of the seven planets the ancients could see, the Sun and Moon ruled one sign each and the rest ruled two — a scheme that stayed tidy until Herschel discovered Uranus in 1781:
Sun → Leo · Moon → Cancer · Mercury → Gemini & Virgo · Venus → Taurus & Libra
Mars → Aries & Scorpio · Jupiter → Sagittarius & Pisces · Saturn → Capricorn & Aquarius
For the outer planets Hone advises the beginner to take Uranus as the main ruler of Aquarius and Neptune of Pisces, and finds that the deep-working forcefulness of Pluto seems to accord with Scorpio. This app’s dignity readings use the traditional rulers for the seven classical planets and the modern rulers for the outer three; you can see a planet’s dignity in its own pop-up and in the Planetary Dignities list under Aspect & Distribution Grids.
Sun → Leo · Moon → Cancer · Mercury → Gemini & Virgo · Venus → Taurus & Libra
Mars → Aries & Scorpio · Jupiter → Sagittarius & Pisces · Saturn → Capricorn & Aquarius
For the outer planets Hone advises the beginner to take Uranus as the main ruler of Aquarius and Neptune of Pisces, and finds that the deep-working forcefulness of Pluto seems to accord with Scorpio. This app’s dignity readings use the traditional rulers for the seven classical planets and the modern rulers for the outer three; you can see a planet’s dignity in its own pop-up and in the Planetary Dignities list under Aspect & Distribution Grids.
▸ The Mathematics — How a Chart Is Calculated
A natal chart is a snapshot of the sky from one place at one moment, written in the language of angles. Turning a birth date, time, and place into that snapshot is pure astronomy — spherical trigonometry applied to a rotating Earth and orbiting planets. Below is the actual pipeline this app runs, and at the end every step is worked through with your own chart’s numbers. None of it asks for belief; it is public-domain astronomy you can check with a calculator.
Step 1 · The Julian Date
Calendars are awkward for arithmetic — leap years, months of unequal length. Astronomers replace them with one continuous count, the Julian Date (JD): the number of days since noon on 1 January 4713 BC. Any instant becomes a single number, and the time of day is just the fractional part. From a Gregorian date it is computed directly:
if month ≤ 2: year −= 1, month += 12
A = ⌊year / 100⌋ B = 2 − A + ⌊A / 4⌋
JD = ⌊365.25 × (year+4716)⌋ + ⌊30.6001 × (month+1)⌋ + day + B − 1524.5
A = ⌊year / 100⌋ B = 2 − A + ⌊A / 4⌋
JD = ⌊365.25 × (year+4716)⌋ + ⌊30.6001 × (month+1)⌋ + day + B − 1524.5
Step 2 · Universal Time
Your birth time is local clock time. To place it against the sky it must first become Universal Time (UT) — Greenwich time — by subtracting your time-zone offset (including any daylight-saving hour). This calculator looks that offset up for you: it identifies the time zone from the birthplace’s coordinates and reads the offset in force on that date from the official IANA time zone database built into your browser, so historical daylight-saving rules are applied automatically. Before standard time zones existed, clocks ran on Local Mean Time, set by the Sun at each town’s own longitude; for those births the offset is simply longitude ÷ 15, as astro.com also does. A second, tiny correction called ΔT converts UT into the perfectly uniform “Terrestrial Time” the planetary tables assume; it is about a minute today and arises from the slow, slightly irregular drift in Earth’s rotation. Small as it is, it matters for fast-moving asteroids passing close to Earth.
Step 3 · Sidereal Time
A Sun-based day is 24 hours, but the Earth turns once against the stars in about 23h 56m — the extra four minutes come from the Earth also moving along its orbit. To know which degree of the zodiac is rising, we need the sky’s own clock, sidereal time. Greenwich Mean Sidereal Time follows straight from the Julian Date; add your longitude and you get Local Sidereal Time, which equals the Right Ascension crossing your meridian — the RAMC.
T = (JD − 2451545.0) ÷ 36525
GMST = 280.46061837 + 360.98564736629 × (JD − 2451545.0)
+ 0.000387933 × T² − T³ ÷ 38 710 000 (mod 360)
RAMC = LST = GMST + longitude // east positive
GMST = 280.46061837 + 360.98564736629 × (JD − 2451545.0)
+ 0.000387933 × T² − T³ ÷ 38 710 000 (mod 360)
RAMC = LST = GMST + longitude // east positive
Step 4 · The Obliquity of the Ecliptic
The zodiac (the ecliptic — the Sun’s yearly path) is tilted against the celestial equator (Earth’s equator projected outward). That tilt, the obliquity ε, is about 23.44°; it is what gives us seasons, and it shrinks by roughly 0.013° per century. Every conversion between equatorial and zodiacal coordinates uses it.
ε = 23.4392911° − 0.0130042° × T − 1.64e−7 × T² + 5.04e−7 × T³
Step 5 · Planetary Positions
Each planet’s place comes from its orbit. Kepler’s laws give where a body sits on its ellipse at a given time; that Sun-centred (heliocentric) position is shifted to be seen from Earth (geocentric), then projected onto the ecliptic to give the zodiac longitude in the chart. High-precision work sums long trigonometric series — VSOP87 for the planets uses hundreds of periodic terms, and the Moon needs its own detailed theory because its orbit is so heavily perturbed. This calculator evaluates such series for the Sun, Moon and planets. Asteroids, centaurs and the distant dwarf planets are handled differently: their orbits are sampled from the Swiss Ephemeris (the engine astro.com uses) at regular intervals, and each position is projected forward from the nearest sample with Kepler’s laws, then corrected for light travel time and aberration. Fixed stars come from the Swiss Ephemeris star catalogue, with each star’s own slow drift across the sky. Every body has been checked against the Swiss Ephemeris, and all agree to within an arcminute from 1800 to 2200.
Step 6 · The Ascendant & Midheaven
Two angles anchor the whole chart. The Midheaven (MC) is where the ecliptic crosses the meridian — the highest point of the zodiac; the Ascendant (ASC) is where the ecliptic crosses the eastern horizon — the rising degree. Both are built from the RAMC, the obliquity, and — for the Ascendant — your latitude φ:
MC = atan2( sin RAMC, cos RAMC × cos ε )
ASC = atan2( cos RAMC, −(sin RAMC × cos ε + tan φ × sin ε) )
ASC = atan2( cos RAMC, −(sin RAMC × cos ε + tan φ × sin ε) )
Using atan2 (rather than plain arctangent) keeps each answer in the correct quadrant of the circle. The Ascendant needs your latitude because the horizon tilts differently the further north or south you stand — and because the RAMC sweeps a full 360° every day, the rising sign changes roughly every two hours. That is why an accurate birth time matters so much: a few minutes can move the Ascendant a whole degree. One subtlety: inside the polar circle the formula can return the setting point instead of the rising one, so the calculator checks which side of the Midheaven it landed on and flips it by 180° when needed, the same rule the Swiss Ephemeris uses.
Step 7 · Dividing the Houses
With the ASC and MC fixed, the twelve houses subdivide the space between them — and here astrologers genuinely disagree, because there is no single “correct” way to slice a tilted circle seen from a spinning sphere. The main systems differ in what they divide:
• Whole Sign (the oldest): the entire sign containing the Ascendant becomes the 1st house, the next sign the 2nd, and so on. Houses simply are signs — each a clean 30°, no trigonometry required.
• Equal House: begin at the exact Ascendant degree and mark every 30° around the ecliptic. It keeps the ASC as the 1st cusp, but the MC no longer lands on the 10th cusp.
• Porphyry: take the ecliptic arcs between ASC and MC and cut each into three equal parts — the earliest “quadrant” system, dividing space evenly.
• Placidus (the most popular today): a time-based system. It follows how long each degree of the ecliptic takes to climb from the horizon to the meridian, and places the intermediate cusps where a degree has completed one-third and two-thirds of that journey. It has no simple closed form — it must be solved by iteration.
• Koch, Campanus, Regiomontanus: these divide different great circles altogether — the prime vertical, or the celestial equator — rather than the ecliptic or time.
• Equal House: begin at the exact Ascendant degree and mark every 30° around the ecliptic. It keeps the ASC as the 1st cusp, but the MC no longer lands on the 10th cusp.
• Porphyry: take the ecliptic arcs between ASC and MC and cut each into three equal parts — the earliest “quadrant” system, dividing space evenly.
• Placidus (the most popular today): a time-based system. It follows how long each degree of the ecliptic takes to climb from the horizon to the meridian, and places the intermediate cusps where a degree has completed one-third and two-thirds of that journey. It has no simple closed form — it must be solved by iteration.
• Koch, Campanus, Regiomontanus: these divide different great circles altogether — the prime vertical, or the celestial equator — rather than the ecliptic or time.
Because each system carves a different circle, the very same planet can fall in different houses under different methods — most dramatically near the poles, where time-based systems like Placidus break down completely (a degree there may never rise at all). This calculator uses Placidus, and inside the polar circle (latitude above about 66.6°) it switches to Porphyry, as astro.com does, with a note in the Houses section when that happens. That geometric ambiguity, not dogma, is the honest reason astrologers argue about house systems: the sky offers several defensible answers, and you choose the lens.
▸ Planetary Longitudes, Visualized — From Orbits to the Zodiac
Where do the planets’ positions come from? Step through the real pipeline this app runs — birth moment → Julian Date → the VSOP87 orbital series → a geocentric shift → an ecliptic longitude for every body. The Sun example is evaluated from genuine VSOP coefficients and lands on your chart’s Sun to under an arcminute. (Orbit diagram is schematic, not to scale.)
Calculate a chart to begin the walk-through.
▸ Ascendant & Midheaven, Visualized — Watch the Angles Emerge
Before houses can be divided, two anchors come from the sky’s rotation and its tilt. Step through the spherical trigonometry that turns sidereal time into your Ascendant and Midheaven — each formula unfolds with your numbers as the meridian and horizon appear on the wheel.
Calculate a chart to begin the walk-through.
▸ House Division, Visualized — Watch the Formula Unfold
Pick a house system, then step through it. The formula unfolds line by line with your numbers, and each cusp is drawn onto the wheel as it is calculated. The angles (ASC / MC) are pink; the cusp being solved glows gold.
Calculate a chart to begin the walk-through.
▸ Learning Center — Quiz & Self-Reflection
⚠ Important — Please Read Before Proceeding
Astrology is a tool for self-reflection and learning, not prediction or excuse-making. The patterns described in a natal chart are symbolic frameworks, not deterministic forces. You always have agency over your choices.
Mental health awareness: Deep engagement with symbolic systems like astrology can occasionally trigger dissociative states, magical thinking, or distorted self-perception — especially in individuals prone to anxiety, OCD, psychosis, or depersonalization. If you notice any of the following, please stop, ground yourself, and consider speaking with a mental health professional:
• Feeling that the chart is controlling your life rather than describing tendencies
• Difficulty distinguishing between symbolic interpretation and literal reality
• Making major life decisions based solely on astrological timing
• Feeling overwhelmed, paranoid, or unable to stop checking planetary transits
• Believing you have special cosmic powers or are uniquely destined
• Using astrological explanations to avoid personal responsibility
This quiz integrates DBT (Dialectical Behavior Therapy) grounding skills at regular intervals to help you stay present, balanced, and connected to reality while learning. These are evidence-based techniques used in clinical practice.