How a Chart Is Calculated
A chart is computed from two snapshots of the sky: your birth moment and a point about 88 days before it. Planet positions map onto 64 gates, and the pattern they activate becomes your bodygraph.
Under the imagery, chart calculation is astronomy. An ephemeris, the same math used by observatories, gives the exact ecliptic longitude of the Sun, Moon, both lunar nodes, and the planets at your moment of birth. Syora runs these figures with Swiss Ephemeris precision rather than lookup tables.
Human Design's addition is a second calculation. Step the Sun back 88 degrees of arc from its birth position, roughly three months earlier in time, and take a full second snapshot there. That prenatal moment is your Design; the birth moment is your Personality. Two sets of thirteen positions, twenty-six activations in all.
Each longitude then lands somewhere on a 360-degree wheel divided into 64 gates of 5.625 degrees, each split again into six lines. Which gates catch your planets, and which of those gates join into channels, determines every defined center, your Type, your Authority, and your Profile.
Two snapshots, one chart
The Personality calculation, from birth, describes the self you consciously identify with; in the chart it's drawn in black. The Design calculation, from 88 solar degrees earlier, is drawn in red and describes machinery you don't watch yourself operate: it shows up in your body language, your reflexes, the way you are when you're not composing yourself. The interplay of the two is why people sometimes feel like a passenger and a driver sharing one vehicle.
From longitude to gate and line
The zodiac wheel is carved into 64 equal gates, and every planetary longitude falls inside exactly one of them. Within its gate, the position falls into one of six lines, each a sixth of the gate's arc. The gate gives an activation its theme; the line gives it a style. Your Profile, for instance, is simply the line of your Personality Sun over the line of your Design Sun.
Why the birth time matters
The Moon crosses a whole gate in about ten hours, and a line in well under two. An uncertain birth time can therefore move activations, occasionally flipping a center from defined to open or shifting your Profile. If your time is approximate, hold the fine details lightly and lean on the parts of the chart that stay stable across the plausible window. The broad strokes usually survive; the decimals may not.
Keep exploring
The conscious side of your chart, calculated from your birth moment. The part of you that you recognize.
The unconscious side, calculated about 88 days before birth. It runs through your body more than your mind.
One of 64 positions in the chart, each a specific flavor of energy. Gates activated at birth are yours for life.
The fine-grained position (1 to 6) within a gate. Lines add a distinct style to a gate's theme.
Human Design is a map of how your energy naturally works, drawn from the time and place you were born. It doesn't tell you who to become. It describes how you already operate when nothing is in the way.