How we calculate your astrocartography map

Planetary positions and sky time

When you enter your birth details, your browser first converts that local calendar date and wall-clock time into Coordinated Universal Time (UTC). From UTC, it computes the true sidereal time at Greenwich. Sidereal time measures the rotation of the Earth relative to distant stars rather than the Sun, tracking the precise angle of the sky above the globe.

Next, we calculate apparent geocentric right ascension and declination of date for ten bodies: the Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. These coordinates describe the planet's real position in the sky, a method called in mundo. Some mapping tools instead use its zodiac degree with zero planetary latitude, known as in zodiaco. The choice can move lines for bodies such as Pluto, Venus, and the Moon; for the Sun, the comparison gives no difference.

The meanings attached to planets and angles come from astrological tradition. The exact part is the geographic calculation, checked to under half a mile (0.7 km) for a supplied birth moment.

The geometry of the four angles

Astrocartography maps track forty lines in total: ten bodies multiplied by four cardinal angles. The angles are MC (Midheaven, where it was highest), IC (Imum Coeli, where it was lowest, underfoot), AC (Ascendant, where a planet was rising), and DC (Descendant, where it was setting).

These lines belong to two distinct geometric families. Upper and lower culminations produce the MC and IC lines. At any given moment, a planet crosses the meridian along a single north–south line of longitude, running straight from pole to pole. The IC line sits on the opposite meridian, exactly 180° of longitude away, where the body reached its lowest point below the feet.

Rising and setting create the curved AC and DC lines. At your birth moment, the planet stood directly overhead (at the zenith) above one exact coordinate on Earth. The geographical horizon is simply a great circle drawn on the globe exactly 90° away in every direction from that overhead spot. Half of this circle marks where the planet appeared on the eastern horizon (the AC line), and the other half marks where it dipped below the western horizon (the DC line). Projected onto a flat map, this continuous circle wraps around the globe in characteristic S-curves and domes.

Polar loops and turning latitudes

Because AC and DC lines form a single continuous circle tilted across the globe, they do not run through every latitude. Near the poles, rising and setting lines meet, curve around, and head back toward the equator.

The turning boundary depends on the planet's declination; beyond it, the planet doesn't rise or set that day. In our Lisbon reference chart, born June 23, 1990, the turning latitudes are Sun 66.6°, Moon 65.8°, Venus 71.8°, Mars 85.2°, and Pluto 88.7°. The Sun's June boundary is near the Arctic Circle. Depending on the day, the Moon's turning latitude can fall anywhere from about 61.4° to the pole.

Shortest-path distances on a sphere

When you click a city, the site shows your distance to nearby lines in miles and kilometers. We measure this distance along a great circle: the shortest curved path across the Earth's surface between your selected city and the nearest point on the line.

Some distance readouts measure purely east–west along a city's parallel of latitude. For straight, vertical MC and IC meridians, both methods yield similar numbers. For slanted AC and DC curves, measuring along the parallel grossly overstates how far away you are.

Consider our sample chart. Measuring from Reykjavik to the Venus DC line along the city's parallel produces an apparent gap of 449 miles (723 km). By the true shortest path over the curved globe, Reykjavik is only 274 miles (441 km) from the line. Similarly, London sits 42 miles (68 km) from the Neptune AC line by the shortest path, compared to 53 miles (85 km) along the parallel.

Time zones, daylight saving, and birth-time sensitivity

A birth chart is only as reliable as its time zone offset. Our calculation applies the time zone database for your birth city and date, accounting for regional shifts, wartime daylight saving quirks, and local clock changes. If your birth occurred during an autumn transition where clocks moved back and an hour occurred twice, our search form asks you to pick the earlier or later instance.

Precision matters because the Earth rotates swiftly. Every hour of birth time shifts the entire planetary map westward by 15° of longitude. That means just 1 minute of birth-time error slides every line by 15 arcminutes of longitude—about 17 miles (28 km) at the equator, and about 13 miles (21 km) at New York's latitude.

A birth-time error of 15 minutes moves your lines by roughly 3.75° of longitude, which translates to about 260 miles (420 km) at the equator. In our sample chart, Lisbon is 69 miles (112 km) from the Jupiter DC line; a ±15-minute window swings that distance anywhere from 0 to 249 miles (0 to 401 km). If you do not have a birth time at all, calculation stops: over a 24-hour day, every MC line sweeps across every single longitude on Earth.

Accuracy benchmarks

We checked our core browser engine against a reference ephemeris used by professional astrology software. Across an automated test suite of 5,000 birth moments spanning from 1900 to 2050, our coordinates align closely with the benchmark.

Every line falls within under half a mile (0.7 km) of the reference coordinates. Straight MC and IC lines match within 22 arcseconds of longitude, and city-to-line shortest-path distances agree within 0.7 km. These figures measure agreement between calculations for known inputs; uncertainty in your birth time remains a separate source of variation.

What we model and what we omit

We use a geometric horizon. We do not apply atmospheric refraction, which bends light near the horizon by about 34 arcminutes (roughly 40 miles (64 km) for AC/DC lines) depending on local temperature and air pressure.

We also bypass topocentric lunar parallax. Viewing the Moon from the surface of the Earth instead of the planet's center introduces a shift of roughly 1° (an estimated 60–70 miles (97–113 km) on the ground). Standard astrocartography omits parallax and refraction to preserve an objective, geocentric model of the sky.

House systems don't alter astrocartography lines. They divide a chart into houses, but changing that setting leaves the rising, setting, highest, and lowest conditions in place. A relocation chart is a related calculation using the same birth moment for another city; changing the location changes its angles and houses.

Data sources and privacy

Our interface uses open geographic data. City search uses GeoNames under CC BY 4.0. The world map uses public-domain Natural Earth data in a Miller projection, and airport codes use OurAirports, also public domain.

The map calculation runs locally in your browser. Your birth details are not sent to a server for processing.