How we calculate

The astronomy behind your chart is checkable. The meaning attached to it is a symbolic system, covered on the About Human Design page.

Positions of the planets

We compute apparent geocentric ecliptic longitudes (true equinox of date) for the Sun, Moon and the eight planets with astronomy-engine version 2.1.19 (MIT license), running in your browser. The Earth position is the Sun plus 180 degrees. Your birth latitude and longitude are not used in the calculation, because every position is measured from the center of the Earth. They are used only to find your time zone.

The true node

The lunar node is the "true" (osculating) node: the ascending node of the Moon's instantaneous orbit, computed from the Moon's position and velocity in the ecliptic of date. We wrote this routine ourselves on top of astronomy-engine's lunar model. The South Node is the North Node plus 180 degrees. We tested a simpler published approximation and rejected it because its errors were large enough to change results.

The Personality side and the Design side

Personality (black) uses the positions at your birth moment. Design (red) uses the positions at the moment the Sun was exactly 88 degrees of ecliptic longitude earlier than at birth. That moment is found numerically, to about a ten-millionth of a degree, and falls roughly 84 to 93 days before birth. This is the Sun-arc method, not "88 days". We show the Design moment in UTC on your chart.

From longitude to gate and line

The zodiac wheel is divided into 64 gates of 5.625 degrees, each into 6 lines of 0.9375 degrees. Gate 41 begins at 2 degrees of Aquarius (302.000 degrees). We use integer arithmetic on 69,120 equal base units so a position exactly on a boundary lands the same way every time. Gates are combined into channels, centers, type, authority, definition, profile and cross using the system's published rules.

Time and time zones

Your local birth time becomes a UTC instant using the IANA time-zone database for the place you choose (the places come from GeoNames, bundled with this site, so searching is offline). We always show the UTC offset used and let you override it. We flag:

• local times that happened twice when clocks went back (you choose which one),
• local times that never existed when clocks went forward (we ask you to check rather than guess),
• births before 1970, where historical time-zone records are less reliable, and
• offsets that suggest local mean time.

If you do not know your birth time, we scan the whole local day and show which parts of your chart stay the same and which could change.

Accuracy

We compared our engine with the Swiss Ephemeris (data-file mode) on 20,000 random moments between 1930 and 2025. Swiss Ephemeris was used only for this test and is not part of the site.

• The Design moment differs from the reference by 14.6 seconds on average, and 84 seconds at most.
• Type, authority, profile and cross differed from the reference in 2 of 20,000 charts (0.01%). The set of channels differed in 0.09%.
• Gate numbers differ for 0.013% of individual activations and line numbers for 0.084%, so in about 2% of charts at least one line is on the edge of its neighbor.
• For colors, tones and bases (finer subdivisions), the difference is larger: about 12% of charts have a color on a boundary, and about 3% have a tone-based arrow that would point the other way. We therefore do not show colors, tones, bases or the "Variables" arrows.

We also compared 16 published reference charts of public figures. 14 matched on every published field and 83 of 87 individual fields matched. Both mismatches traced to the recorded birth time, not the calculation. The birth data for these tests was recalled from public records and has not all been verified at the source, so please treat that figure as encouraging rather than conclusive. A birth time that is off by a few minutes matters far more than the arcseconds above.

The full validation report and the test suite are available to reviewers on request.

Credits and licenses

• Planetary positions: astronomy-engine by Don Cross, MIT license.
• Time handling: Luxon, MIT license, with the IANA time-zone database.
• Places: GeoNames cities with population over 15,000, licensed under Creative Commons Attribution 4.0. We reformatted the data into a compact file.
• The chart drawing, the explanations and the site design are original to Orrery Lane. We are not affiliated with Jovian Archive and use no one else's artwork or text.