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Birth charts: data, calculations and reading the wheel
A birth chart represents the positions of celestial bodies at a particular instant. Astronomical calculations should be distinguished from astrological interpretation.
Start with reliable family records
Create a family-tree branch and add the person. Transcribe birth date, time and place from family documents or relevant official records. Mark an approximate time as such: a few minutes can affect the ascendant and houses. Check branch visibility before sharing and avoid publishing living people’s details without their agreement.
Why do place and time zone matter?
Clock time is not necessarily UTC. A place may have changed its time zone or daylight saving rules over the years. Select the birth city to fill coordinates and the IANA time zone automatically, starting with the place saved in the profile. For duplicate city names, choose the correct country and region. You can review the coordinates and zone in advanced options. If the clock moved back and the time occurred twice, choose the correct occurrence. Nonexistent times are not silently converted. Historical time-zone data before 1970 may require additional documentary checks.
Reading the wheel
The outer ring shows twelve signs. Each dot marks the actual longitude of a body; a leader line connects it to its symbol to avoid overlapping labels. The table shows degrees and minutes within each sign. R indicates apparent retrograde motion as seen from Earth. Select a body from the table, hide houses or aspects, and download the chart as PNG or SVG.
Equal houses
The chart uses equal houses: twelve 30° sectors beginning at the ascendant, not Placidus houses. The midheaven is calculated separately and need not coincide with the 10th house cusp. Displayed aspects are conjunction, sextile, square, trine and opposition with a maximum 6° orb; this selection is an interpretive convention.
Calculation method
Tropical zodiac, apparent geocentric positions on the ecliptic of date, and 30° equal houses starting at the ascendant. The midheaven is calculated separately: it is not necessarily the 10th house cusp. Astronomy Engine 2.1.19, MIT license.
This version supports Gregorian dates from 1800 to 2100. At absolute latitudes of 66° or more, ascendant and houses are omitted because that case has not been validated. Displayed minutes are not a universal precision guarantee: accuracy also depends on the original birth records.
Astrology is an interpretive practice, not a scientific prediction. Accuracy depends on birth data. Historical time zones before 1970 may be uncertain; dates use the Gregorian calendar.
Astronomical calculations run in your browser without sending data to external astrology services. Personal charts are not indexed.