The Charts · The master chart
Your sun sign is one line of it. This is the whole page.
What is a birth chart?
A birth chart, or natal chart, is a map of the sky at the minute and place you were born: where the Sun, Moon and planets stood along the zodiac, which sign was rising in the east, and the angles between them. Astrologers have drawn them since the first known horoscopes of 410 BCE.
On your card: pages 2 and 3 Your birth chart, Your placements, Your aspects, The sky the day you arrived, Your generation
What it is
A birth chart is a snapshot. Freeze the sky at the minute you were born, as it looked from the town you were born in, and write down where everything was. That record, a list of positions usually drawn as a wheel, is the chart. Astrologers also call it a nativity, a natal chart or a horoscope. The last word comes from the Greek horoskopos, the "hour-watcher": the part of the zodiac rising on the eastern horizon at the moment of birth. 1
Nothing in the positions is made up. They are astronomy, the same numbers an astronomer would get for that minute. What astrology adds is interpretation: a tradition of meanings, built up over two and a half thousand years, for each planet, sign, house and angle.
Your sun sign is one line of the chart. A full chart has ten bodies (the Sun, the Moon, and Mercury through Pluto, which astrologers still count), each in a sign, plus the rising sign and the Midheaven. That is why two people with the same sun sign can turn out so different.
How a chart is made
Five steps. The machine does them the way an astronomer would, then a sixth no astronomer would: it reads them.
- Fix the moment. Your birth date, clock time and time zone give one exact instant in Universal Time. The local time on a birth certificate has to be converted with the clock rules in force that day, daylight saving included.
- Place the planets. For that instant, an ephemeris (once a printed table, now a program) gives each body's position along the ecliptic, the Sun's yearly path across the sky. Positions are measured in degrees from 0° Aries, the Sun's place at the March equinox, and every 30° is one sign. 2
- Find the horizon. Your birthplace's latitude and longitude, with the time, show which degree of the zodiac was crossing the eastern horizon (the Ascendant) and which was crossing the meridian overhead (the Midheaven). These are the chart's angles. 3
- Divide the houses. The circle is cut into twelve houses counted from the Ascendant, each one standing for an area of life in the tradition.
- Measure the aspects. Last, the angle between every pair of bodies is checked against the classical aspects: together, 60°, 90°, 120° and 180° apart. 4
How to read a chart wheel
An example of the structure only. No planets, no birthday, nobody's chart.
- The signs. The outer ring is the zodiac: twelve equal signs of 30°, running counter-clockwise from Aries.
- The houses. The numbers inside are the houses. This example has Aries rising, so with whole-sign houses Aries is the 1st house, Taurus the 2nd, and so on round to Pisces, the 12th.
- The angles. AC is the Ascendant, drawn on the left because that is east; DC, the Descendant, sits opposite. MC, the Midheaven, is near the top and IC near the bottom.
- The centre. In a real chart, planet symbols sit on the ring at their degrees, and lines across this disc join the pairs that make aspects. They are left out here on purpose.
Houses, and why the machine uses whole signs
Signs come from the Sun's yearly path and are the same for everyone born on a given day. Houses come from the Earth's daily spin: they depend on the minute and the place, and the whole set turns once a day. An old shorthand puts it this way: the sign says how a planet acts, the house says where in life it shows.
There are many ways to cut the houses. Whole-sign houses, probably the oldest system, make the entire rising sign the 1st house, the next sign the 2nd, and so on, so every house is exactly one sign. Quadrant systems such as Porphyry and Placidus start the 1st, 4th, 7th and 10th houses at the four angles and divide the space between, so their houses come out in uneven sizes. 3
Placidus is the most widely used system today, perhaps because its tables were printed in Raphael's Ephemeris; Koch tables were not published until 1971. The historian James Holden identified whole signs as the house system of Hellenistic astrology, and Robert Hand calls them probably the earliest. 3
The machine uses whole signs for three plain reasons. They are the oldest system on record. They work at every latitude, while some quadrant systems, Koch among them, break down near the poles. And anyone can check them by hand: if your rising sign is Virgo, your 7th house is Pisces, and that's that. 3
One side effect: with whole signs the Midheaven does not have to open the 10th house. Depending on the latitude and the time, it can land in the 8th, 9th, 10th or 11th. 3
Aspects: the angles between planets
An aspect is an angle. Ptolemy counted five: the conjunction (together), the sextile (60°), the square (90°), the trine (120°) and the opposition (180°). They are still the five major aspects. 4
Planets are seldom exactly 120° apart, so each aspect is given an orb, an allowance either side of exact. The machine uses a common modern set: 8° for conjunctions and oppositions, 7° for trines and squares, 5° for sextiles, and 2° more when the Sun or Moon is one of the pair.
Tradition calls trines and sextiles easy angles and squares and oppositions hard ones. Drawn on a wheel, the two kinds usually get different colours or line styles so you can tell them apart at a glance.
Why the time and place matter
The Sun moves about a degree a day, so the date almost always settles your sun sign. The Moon goes round the Earth in about 27 days, roughly 13° a day, and changes sign every two to three days, so for many birthdays the date leaves it open. The rising sign changes about every two hours, and the houses with it, so with no time there is no rising sign and no houses at all. 5
Place matters for the same reason. At a single instant the sign rising in Toronto is not the sign rising in London. The planets' signs are the same all over the world; the angles and houses are not.
Ptolemy was already worried about this in the 2nd century. A birth hour is hard to pin down, he wrote: sundials shift and water clocks clog, and only an astrolabe can give the minute. He set out a method for estimating the rising degree when the time was uncertain. 6
Without a time, the machine works the chart out for noon on your birth date, flags any planet that changed sign that day, leaves the rising sign, angles and houses off, and says so on the card. With a time and a town, the whole chart opens up.
The sky that day, and your generation
Beside the chart proper, the machine notes things an astronomer would recognise: the phase of the Moon, which planets were retrograde, and whether an eclipse fell near your birthday. Retrograde motion is a trick of viewpoint. Earth overtakes a slower outer planet on the inside track, and for a few weeks the planet seems to drift backwards against the stars. 7
The slowest planets take a lifetime or more to go round the Sun: Uranus about 84 years, Neptune about 165 and Pluto about 248. Each stays in one sign for years, so everyone born within a few years of you shares those signs. Astrologers read them as markers of a generation rather than of a person. 8,9,10
Where the birth chart comes from
Era by era, with sources. More in the Reading Room.
- Babylonearly 7th century BCEIn Assyria a specialist class of diviner, the Scribe of Enuma Anu Enlil, reads the sky for the king from a series of about 70 tablets of celestial omens. The omens warn the court about war, the ruler and his family, not about private people. 11,12
- Babylonc. 450 BCEAfter a thousand years of development the zodiac settles into twelve equal signs along the path of the Moon and planets, each divided into 30 units, our degrees. 11,1
- Babylon410 BCEThe earliest known horoscopes, from Babylon and Nippur. Most surviving Babylonian horoscope tablets list a birth date and the signs of the Sun, Moon and five planets, and almost never a reading. 11,1
- Hellenistic1st century BCEGreek astrologers in Egypt take up Babylonian horoscopy and add the horoskopos, the rising point, which gives the horoscope its name. About 200 Greek horoscopes survive, mostly papyri, worked out from tables rather than by watching the sky. 1
- Roman Egypt2nd century CEPtolemy, in Alexandria, writes the Tetrabiblos: the five aspects, the planets' rulerships, and an argument for why the sky should matter at all. 13,4
- Roman Egypt152–162 CEVettius Valens, born in Antioch in 120 CE and working in Alexandria, writes most of his Anthologies: nine books with about 130 example horoscopes, the largest practical astrology manual to survive from antiquity. 14
- Islamic golden age9th centuryThe Persian astrologer Abu Ma'shar (died 886) writes an introduction to astrology that is later translated into Latin and read across Europe. The University of Edinburgh holds a 12th-century Latin copy. 15
- England1647William Lilly publishes Christian Astrology in London, a three-book manual in English that covers using an ephemeris, setting up a chart, the signs and planets, and judging nativities. 16
- Victorian1890Alan Leo's Astrologer's Magazine first goes on sale. Annual subscribers get a free horoscope: birth charts by post, for ordinary readers. 17
- Psychological turn1936Dane Rudhyar's The Astrology of Personality joins astrology to Carl Jung's psychology and reads the chart as a picture of character rather than a list of predictions. 18
- Computers1972Neil Michelsen, after seventeen years at IBM, founds Astro Computing Services and prints computer-calculated charts at low prices. His American Ephemeris volumes later cover a century at a time. 19
- Computers1980–1996Astrodienst in Zürich starts selling colour birth charts in 1980 and goes online in 1996: a chart in seconds, for anyone with a modem. 20
- Today2025A Pew Research Center survey finds that 30% of US adults consult astrology, tarot or a fortune teller at least once a year, mostly for fun. 21
Asked at the booth
Do I need my birth time for a birth chart?
For part of it. The date gives the signs of the Sun and of every planet from Mercury to Pluto, and often the Moon. The rising sign, the Midheaven and the houses need the time and the place, because they turn once round the whole zodiac every day.
What if I don't know my birth time?
Look for it on a long-form birth certificate, a hospital record or a baby book. Without it, the machine works from noon on your birth date, tells you which parts it cannot be sure of, and leaves the rising sign and houses off rather than guessing.
Is a birth chart the same as a horoscope?
Originally, yes. Horoscope comes from the Greek name for the rising point of the chart, and for centuries it meant the whole birth chart. The newspaper horoscope, which uses only the sun sign, is a 20th-century offshoot.
Why does my chart look different on another website?
Usually the house system. Many websites default to Placidus houses; the machine uses whole signs, so a planet can sit one house over. The signs and degrees of the planets should match to within a fraction of a degree. A sidereal (Vedic) chart will differ by about 24°, because it measures from the stars rather than the equinox.
Which planets does the machine use?
The Sun, the Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto, plus the Ascendant and Midheaven when it has a birth time and place. Positions come from astronomy-engine, an open-source astronomy library, in the tropical zodiac Western astrology uses.
Is astrology a science?
No. The positions in a chart are astronomy and anyone can check them; the meanings given to them are tradition. In Shawn Carlson's double-blind test, published in Nature in 1985, astrologers matched charts to personality profiles no better than chance. The card is for entertainment and self-reflection.
Go deeper
- Moon SignWhat is your moon sign, and how is it worked out?
- Rising SignWhat is a rising sign, and why does it need a birth time?
- Love ChartWhat is a love chart in astrology?
- Sun SignsAll twelve sun signs, with dates and history
- Returns and CyclesWhat are planetary returns and numerology's turning points?
- GenerationsWho names the generations, and why do the years disagree?
- AspectWhat is an aspect in astrology?
- ElementWhat is an element in astrology?
- Ruling planetWhat is a ruling planet?
That's how it works for everyone. Your card works it out for you.
This page explains the method and where it comes from. What it says about you is sealed on your card, worked out from the day, the minute and the place you were born.
What your card covers
See all six pages, sealedFold the pages back
1 Who you are
2 The machine says
3 Your sky
4 Love & your people
5 Work & money
6 Your year ahead
Sources
- Alexander Jones, The Horoscope Casters (Archaeology Odyssey 3.6, 2000), New York University Faculty Digital Archive. Read on .
- Constellations and the Calendar, NASA (from NASA Space Place), 20 September 2016. Read on .
- The Astronomy of Houses, The Urania Trust (Graham Bates, 2013–2014; posted 13 June 2016). Read on .
- Ptolemy, Tetrabiblos, Book I, chapters 10–19 (aspects, houses of the planets, triplicities), LacusCurtius, University of Chicago (Loeb Classical Library translation by F. E. Robbins, 1940). Read on .
- Moon Facts, NASA Science. Read on .
- Ptolemy, Tetrabiblos, Book III, chapters 1–9 (chapter 2: Of the Degree of the Horoscopic Point), LacusCurtius, University of Chicago (Loeb Classical Library translation by F. E. Robbins, 1940). Read on .
- January's Night Sky Notes: The Red Planet, NASA Science, Night Sky Network (Kat Troche, 1 January 2025). Read on .
- Uranus: Facts, NASA Science. Read on .
- Neptune: Facts, NASA Science. Read on .
- Pluto: Facts, NASA Science. Read on .
- Review of Francesca Rochberg, The Heavenly Writing: Divination, Horoscopy, and Astronomy in Mesopotamian Culture (reviewed by Eleanor Robson), BMCR 2005.06.29, Bryn Mawr Classical Review. Read on .
- Astrology, Encyclopaedia Britannica. Read on .
- Ptolemy (by Alexander Raymond Jones), Encyclopaedia Britannica. Read on .
- The Logic of Planetary Combination in Vettius Valens, ISAW Papers 24 (2023), NYU Ancient World Digital Library (Claire Hall and Liam P. Shaw, Oxford University). Read on .
- 'Dicta Albumassar' by Abu Ma'shar, a Latin version of his Introduction to Astrology, 12th century, University of Edinburgh Archives and Manuscript Collections. Read on .
- William Lilly, Christian Astrology: Modestly Treated of in Three Books (London, 1647), Wellcome Collection (electronic reproduction of the Library of Congress copy, Early English Books Online). Read on .
- The Life and Work of Alan Leo, Theosophist, Astrologer, Mason, Internet Archive (digitised book: Bessie Leo and others, London, 1919). Read on .
- Dane Rudhyar (1895–1985), Skyscript (Mari Garcia and Joy Usher, March 2012). Read on .
- Neil Michelsen (1931–1990), The Urania Trust, 28 February 2016. Read on .
- About Astrodienst, Astrodienst AG (company history). Read on .
- 30% of Americans Consult Astrology, Tarot Cards or Fortune Tellers, Pew Research Center, 21 May 2025 (Chip Rotolo). Read on .