convert longitude to date

[arumdyaharum]

is it possible to convert from longitude to date?

for context, human design uses two astrology charts. the first chart is from our birthtime, the second chart is 88° backward from birthtime sun longitude. I get sun correctly but I need sun date in order to know the rest of the second chart.

[cosinekitty]

Sorry, I don't understand this question. I keep re-reading this but I can't figure out what you mean.

[arumdyaharum]

So I'm trying to create human design chart that looks like below. It uses 2 astronomical position, design side and personality side. personality side is created from the time when we born. design side is created from 88° backward or around 85-95 days before we born.

my approach is I get the longitude of whole planetary position of the personality side from birthtime first. and then I get design sun by subtract personality sun by 88. in order to know the rest planetary position of the design side, I need to know the date of the design side.

I asked people from human design community and they said I can search manually around 85-95 days before birthtime and look at the closest longitude with accuracy of 5 decimal places.

here's my code.

function geoVectorToDegree (date, planet) {
  const vector = Astronomy.GeoVector(PLANETS[planet], Astronomy.MakeTime(date), true);
  let longitude = Astronomy.Ecliptic(vector).elon;
  // Convert 180 format to 360 format
  if (longitude < 0) longitude = longitude + 360;
  return longitude;
}

function hdCreation (date, isDesign = false) {
  const sunDegree = geoVectorToDegree(date, "sun");
  const sun = degreeToHdGates(isDesign ? sunDegree - 88 : sunDegree);
  const earth = degreeToHdGates(isDesign ? sunDegree - 88 + 180 : sunDegree + 180);
}

[cosinekitty]

OK, that explanation helps. I recommend calling SunPosition to find the Sun's longitude at the birth date. It returns type EclipticCoordinates, which contains the Sun's ecliptic longitude in the variable elon.

Once you have that, subtract 88 degrees, and pass the result to SearchSunLongitude. The resulting code could look something like this:

const birth = Astronomy.MakeTime(new Date('2023-06-12T00:00:00Z'));
const sun = Astronomy.SunPosition(birth);
const target = ((sun.elon - 88) + 360) % 360;
const design = Astronomy.SearchSunLongitude(target, birth.AddDays(-100), 100);
console.log(design.date);    //  2023-03-13T16:03:31.528Z

[arumdyaharum]

Thank you @cosinekitty. I have one more question regarding lunar nodes. astrology and human design treat lunar nodes as a planetary position so it's important to know the longitude of lunar nodes through time. am I need to create another discussion or create new issue?

[cosinekitty]

Yes, please start a new discussion. We keep the discussions around so other people can read them later, so it helps to keep the topics organized. Thank you!