Sidereal Vedic chart using Lahiri Ayanamsha and whole-sign houses. Here's the detail behind that one line.
Solar and lunar positions use the Meeus solar/lunar series; the other planets use Standish J2000 planetary elements. In practice this is accurate to about 1 arc-minute for the Sun and Moon, and a few arc-minutes for the other planets — genuinely good for everyday chart reading, dashas, yogas, and most Muhurta work.
It is not (yet) precise enough for birth-time rectification or the most exacting, minute-level Muhurta timing, where a few arc-minutes of drift can matter. We're upfront about this rather than overselling the tool's precision — a future upgrade to Swiss-Ephemeris-grade precision is on our roadmap for exactly those use cases.
We use Lahiri (Chitrapaksha) ayanamsha, the standard reference point for modern Vedic astrology, to convert tropical positions to sidereal.
Rahu and Ketu are calculated using the mean node by default.
Whole-sign houses (Bhava) — the sign containing the Ascendant is the whole 1st house, the next sign is the whole 2nd house, and so on. No house interceptions.
Your birth time is converted to UTC using your birth city's real historical timezone rules — including daylight saving, resolved for your exact birth date, not a single fixed offset. This matters: a city's UTC offset can differ by an hour or more between summer and winter, and using the wrong one shifts your Ascendant and every house. If you entered your city by searching for it, this is handled automatically; if you entered raw latitude/longitude and a manual UTC offset instead, that value is not automatically DST-corrected, and you're responsible for entering the correct historical offset for your exact birth date.
Sunrise is calculated for a sea-level horizon using the standard atmospheric refraction value of 34 arc-minutes. That value dates from Newton, and it does not account for how refraction actually varies with temperature, pressure, season or latitude — so observed sunrise can differ from any calculated sunrise by roughly two to five minutes. This is true of every astrology program, ours included; it is a limit of the physics, not of the software.
It matters because a handful of points are derived from sunrise rather than from planetary positions, and the fastest of them amplify the error. A five-minute shift in sunrise moves Bhāva Lagna about 1.25°, Ghāṭikā Lagna about 6°, and Prāṇapada Lagna about 25° — very nearly a whole sign. Gulika and the other upagrahas move too. Treat sunrise-derived points as approximate whenever they fall near a sign boundary, and be especially wary of building an interpretation on Prāṇapada's exact position.
Everything else is unaffected: planetary longitudes, the Ascendant, all sixteen divisional charts, every dasha system, ashtakavarga and the yogas are computed from positions and sidereal time, not from sunrise.
For a birth on a ridge or coast, where the land genuinely falls away to the east, the horizon sits below the astronomical horizon and the Sun clears it earlier. Rohshan offers an optional elevation correction for exactly that case. It is off by default and deliberately not automatic, because most high-altitude cities sit on plateaus or in valleys where the surrounding land is as high or higher — applying an elevation correction there would move sunrise several minutes in the wrong direction.
Prashna (horary astrology), birth-time rectification, and the highest-precision Muhurta timing all wait on a future ephemeris upgrade — we'd rather ship these once they can be genuinely precise than ship an approximate version now.
See our FAQ, or contact us directly.