Ved Astra: Designing an Offline-First Astrological Chart Engine

March 30, 2026

Re-thinking Astrological Software

Most astrological services require sending coordinates, birth dates, and exact times to remote servers to generate birth charts. This data is deeply personal and easily linkable to individual profiles.

Ved Astra was built to solve this privacy gap by running all astronomical planetary calculations entirely inside the user's browser.

Celestial Mathematics: The Julian Date

To calculate precise planetary coordinates, the engine must first convert standard Gregorian calendar dates and times (in UTC) into a continuous astronomical scale known as the Julian Date (JD).

The Julian Date represents the number of days elapsed since January 1, 4713 BC. Below is the mathematical calculation algorithm implemented in Ved Astra to compute the Julian Date:

Given year Y, month M, day D, and fractional hour H:

1. If M is less than or equal to 2, set Y = Y - 1 and M = M + 12.
2. Calculate the century adjustment factor A: A = Math.floor(Y / 100) B = 2 - A + Math.floor(A / 4)
3. Calculate the Julian Day number: JD = Math.floor(365.25 * (Y + 4716)) + Math.floor(30.6001 * (M + 1)) + D + B - 1524.5 + (H / 24)

Here is our clean TypeScript implementation of this calculation:

// Calculate Julian Date from UTC calendar values
export function getJulianDate(year: number, month: number, day: number, hoursUtc: number): number {
let Y = year;
let M = month;

if (M <= 2) {
Y = Y - 1;
M = M + 12;
}

const A = Math.floor(Y / 100);
const B = 2 - A + Math.floor(A / 4);

const julianDay = Math.floor(365.25 * (Y + 4716)) + 
Math.floor(30.6001 * (M + 1)) + 
day + B - 1524.5 + (hoursUtc / 24);

return julianDay;
}

Calculating the Ascendant & House Cusps

Once the Julian Date is computed, the engine calculates the Local Sidereal Time (LST) using the user's local longitude. LST represents the orientation of the local meridian relative to distant stars.

Using the LST and the local latitude (lat), we calculate the Ascendant coordinate (the point of the ecliptic rising on the eastern horizon) using spherical trigonometry:

Let e be the obliquity of the ecliptic (approximately 23.44 degrees): Ascendant = Math.atan(Math.sin(LST) / (Math.cos(LST) * Math.cos(e) - Math.tan(lat) * Math.sin(e)))

Ved Astra supports both the Equal House System (where each house is exactly 30 degrees wide starting from the Ascendant coordinate) and the Placidus House System (which divides the sky based on time periods of celestial ascent). By keeping the math in the client, these conversions run instantaneously.

Vector Layout Drawing: Dynamic SVG Renderers

To render the charts (e.g. North Indian or South Indian styles) on mobile and desktop screens, Ved Astra parses coordinates directly into vector graphics.

Instead of downloading heavy static images or loading canvas pixels, our layout engines translate the raw house degrees directly into inline SVG polygons. This layout method keeps the DOM footprint small and guarantees crisp charts at any screen magnification.