Your birth chart is calculated from the exact time and place you were born. Planetary positions are calculated precisely. Sources and licences are listed on Credits.
Birth time and place
The date, time, and place you enter are the inputs. A one-minute clock error or a wrong town changes Rising and the houses more than any rounding in the positions.
Planetary positions
We calculate the Sun through Pluto, the lunar nodes, and True Lilith by default. Mean Lilith is available when you ask for it. Ceres, Pallas, Juno, Vesta, and Chiron are included for births from 1600-01-01 through 2500-12-31. Charts can be calculated for births from 1550-01-01 through 2650-01-24.
Times before 1972 use the historical civil time of that era. From 1972 we use UTC.
House systems
When a birth time is known, the free chart uses Placidus. The calculator can produce 22 house systems; they are listed on House systems. At high latitudes, Placidus and Koch fall back to Porphyry, and the chart names that fallback.
Not sure of your birth time? Choose Time unknown and you still get the planets in their signs. See Unknown birth time. You can choose a noon chart at 12:00 in the birth time zone. Rising and houses in that chart are for noon, so they are approximate.
Time zones
We use the historical civil time of the place you were born. If the record is in local mean time, the offset is taken from the birthplace longitude. If a zone name is missing, we resolve one from the coordinates.
Finding a birthplace
The place you type is used only to look up coordinates. It is never placed in a URL. When the place list is connected, we search a city gazetteer. If it is not connected, a bundled list of well-known cities is the fallback. If your birthplace is missing, pick a larger nearby city only if you understand the chart will use that city’s coordinates and time zone.
Published sample moments
Two published sample moments are used to check the calculated positions: Ulm, 14 March 1879, and London, 21 April 1926. The measured figures are listed on Credits.
