Birth Chart
Calculator

A birth chart, or natal chart, records the sky for one minute at one place. It gives the position of the Sun, the Moon and each planet along the ecliptic, the path the Sun appears to trace through the year, and it fixes which degree of the ecliptic was rising in the east, which was setting in the west and which was crossing the meridian. Those last three points, the Ascendant, Descendant and Midheaven, turn with the Earth once a day, which is why a chart needs the clock time and the place as well as the date.

“Tropical” names the zodiac the positions are counted in. Each sign is a 30° slice of the ecliptic measured from the point where the Sun stands at the March equinox, so a tropical sign places a planet relative to the seasons rather than to a constellation. Most Western astrologers work in this zodiac, and every chart on this site uses it.

Sidereal astrology, the standard in India, counts the same 30° slices from a starting point tied to the stars. The gap between the two starting points widens by about 1° every 72 years. At Barack Obama's birth it was 23°19′ under the Lahiri convention (the value our ephemeris gives for that moment), so any body in the first 23°19′ of a tropical sign falls in the sign before it in a sidereal chart. In his chart that moves eight of the ten planets and the Ascendant:

Only Saturn and Uranus keep their signs, because each sits more than 23°19′ into its tropical sign. Neither zodiac corrects the other, and sign readings written for one don't carry over to the other.

The form sends our API the date, the clock time, the town's coordinates and the name of its time zone. The town list holds 2,292 cities, each stored with its IANA time zone. A place found through the wider search brings coordinates but no time zone, and its birth time is then read as Universal Time, so a listed city in the same zone is the safer choice.

The API converts the clock time to Universal Time with the IANA time zone database, which carries each place's past daylight-saving rules. Honolulu has kept standard time, ten hours behind UTC, since 1947, so 7:24 PM on August 4, 1961 there is 5:24 AM UTC on August 5, 1961. Times in the hour that repeats or is skipped when clocks change are handled as set out on the methodology page.

The API's ephemeris, which is built on NASA JPL's DE431, then gives each body's longitude as seen from the Earth's center, measured from the true equinox of the date. The chart carries the ten planets; the true lunar node, with the South Node 180° opposite; Chiron; Black Moon Lilith, taken as the mean lunar apogee; and Ceres, Pallas, Juno and Vesta. A body whose longitude was decreasing at the birth moment is marked ℞, retrograde.

The house calculation returns the Ascendant, Midheaven and Vertex along with the twelve cusps. Two more results depend on them: the chart counts as a day chart when the Sun is above the horizon, judged from the true Ascendant, and the Part of Fortune reverses its formula by night. From the API code:

Inside 1800 to 2399, the span the ephemeris covers at full precision, positions are good to well under an arc-second. The chart prints them cut to the whole arc-minute: Obama's Sun, at 12°32.87′ Leo, shows as 12°32′ Leo, where a program that rounds shows 12°33′ Leo.

Aspects and Orbs on the Wheel

The wheel and the aspect table use the API's orbs, which the methodology page lists. Each aspect has a base orb, and each pair of bodies scales it by the average of their two multipliers: wider for the Sun and Moon, narrower for Jupiter and Saturn, the asteroids, the outer planets and the points. In the worked example below, the Moon–Jupiter trine is allowed 7.4° and the Neptune–Pluto sextile 3.5°. Two bodies are in aspect when the angle between them is within that orb of the exact value; each pair gets at most one aspect. The minor aspects appear only when Minor Aspects is switched on in Chart Preferences.

The closer an aspect is to exact, against the orb its pair is allowed, the darker and thicker its line. Between any two bodies the wheel shows, it draws the aspect the API's own list gives them. The API also searches that list for T-squares, grand trines, yods and stelliums; the worked example below shows what it finds in one chart.

The houses divide the chart into twelve sectors counted from the Ascendant. The chart opens in Placidus, and Chart Preferences switches to Whole Sign or Equal, which asks the API for the chart again with the new cusps. The planets stay where they are; only the house lines move.

• Placidus divides the time each degree of the ecliptic takes to climb from the horizon to the meridian into thirds. Its 1st, 4th, 7th and 10th cusps are the Ascendant, IC, Descendant and Midheaven, and the houses come out unequal, more so the farther the birthplace is from the equator. Inside the polar circles, where some degrees never rise or set, Placidus can't be computed for some or all birth times.
• Whole Sign gives each house one whole sign: the rising sign is the 1st house, the sign after it the 2nd, through all twelve. Because the house lines would fall on the sign boundaries, the wheel leaves out the house ring and you count houses by sign from the rising sign. The Ascendant and Midheaven become points inside houses rather than cusps.
• Equal starts the 1st house at the Ascendant degree and adds 30° for each house after it. The Midheaven is then a separate point that rarely falls on the 10th cusp.

The choice matters more than it may seem. In Obama's chart, eight of the ten planets sit in a different house under Whole Sign than under Placidus. Jupiter at 0°51′ Aquarius is the clearest case: it lies 17° before the Ascendant, so Placidus puts it in the 12th house, while Whole Sign puts it in the 1st, because it shares the Ascendant's sign. The full comparison is in the worked example below.

This guide reads one chart the way the calculator draws it: Barack Obama's, born at 7:24 PM Hawaii time on August 4, 1961, in Honolulu; the time is from his birth certificate. Entered in the form with Honolulu picked from the list, the chart opens in Placidus houses with the values below, which come from our production API. The example is here to show how to read the chart, so it makes no claims about his life.

The Wheel

1. Find the Ascendant. In the default Ascendant-aligned view, the Ascendant (18°03′ Aquarius) sits at 9 o'clock and the houses run counterclockwise from it: the 1st just below the left end of the horizon, the 7th from 3 o'clock, and the 10th from the Midheaven (28°53′ Scorpio) near the top. Switching to Zodiac-Aligned puts 0° Aries at 9 o'clock instead.
2. Read the horizon. The line from the Ascendant to the Descendant is the horizon: houses 7 to 12 are above it and 1 to 6 below. Here six planets are above (Mars, Jupiter, Saturn, Uranus, Neptune and Pluto) and four below (Sun, Moon, Mercury and Venus).
3. Day or night. The Sun is in the 6th house, 5°30′ short of the Descendant: it had already set, so the API labels this a night chart, and the Part of Fortune uses the night formula.
4. The Big Three. Sun 12°32′ Leo in the 6th house, Moon 3°21′ Gemini in the 4th, Aquarius rising. The report card prints all three at the top left, with the AC and MC degrees under them, and lists the planets and points with their degrees and any ℞ mark down the right side.

The Aspect Table

The triangle at the bottom left of the report lists the ten planets down the side and along the bottom. Find one planet's row and another's column: the symbol where they meet is the aspect between them, blue for sextiles and trines, red for squares and oppositions, purple for the quincunx and green for conjunctions. This chart has 11 among the ten planets:

• The closest is Saturn quincunx Uranus, 0.06° from exact.
• Jupiter and Saturn are conjunct though they sit in different signs, 0°51′ Aquarius and 25°19′ Capricorn: aspects are measured in degrees, so a conjunction can cross a sign boundary when the bodies are 5.53° apart.
• The widest, Mercury opposition Saturn at 7.00°, still counts because that pair is allowed 7.4°: the 8° base orb times the average of 1 for Mercury and 0.85 for Saturn. A program with one orb per aspect for every planet may list a different set.
• The wheel draws 34 lines, many more than the table, because it also joins the node, Chiron and the four asteroids it shows.

Element and Mode Balance

Counting the ten planets by the element of their sign gives 3 fire, 3 earth, 2 air and 2 water; by mode, 5 fixed, 3 mutable and 2 cardinal. The report card counts all 20 bodies the API returns, the node, Chiron, Lilith, the asteroids, the Part of Fortune and the Vertex included, so its figures are larger: F:7 E:6 A:3 W:4 and C:4 F:10 M:6. Compare like with like when you check a balance against another source.

Shape and Configurations

The ten planets span 238° of the zodiac, leaving an empty arc of 122° from Jupiter at 0°51′ Aquarius round to the Moon at 3°21′ Gemini. The Chart Pattern Analyzer, which classifies charts by Marc Edmund Jones's shapes, calls this a Bucket: Saturn and Jupiter, 5.5° apart, form the handle on the far side of a 77° gap, and the other 8 planets fall within 155°.

Among the ten planets alone there is no T-square, grand trine, yod or stellium. The API's configuration search, which also counts the angles, the points and the asteroids, reports 13 (8 T-squares, 3 grand trines and 2 yods), and every one of them needs at least one of those extra bodies. Programs disagree about patterns mostly because they disagree about which bodies to include.

Retrograde Planets

Jupiter and Saturn carry the ℞ mark. Each was within 18° of opposition to the Sun, the stretch of an outer planet's cycle when the Earth overtakes it and its longitude runs backward for a few months.