About
Astrology can be soft. The astronomy shouldn’t be.
AstroSiddhant exists because most free chart sites get the hard part wrong. Nobody can tell, because a wrong chart still looks like a chart.
01 · Why this exists
Why we built it
Ask three free astrology sites for the same chart. You will often get three different Ascendants. That is not because astrology is vague. It is because the arithmetic underneath was done carelessly. Timezones are the usual culprit. A birth in Mumbai in 1950 was recorded on a city clock running 39 minutes behind Indian Standard Time. A site that ignores that puts your Ascendant about 10° out. Often in the wrong house. Sometimes in the wrong sign.
That kind of error is invisible. The chart still renders. The glyphs still look convincing. You would only catch it by checking the working, and almost nobody publishes theirs.
So we built the opposite. The engine is tested against outside references. The site tells you what it does not know.
02 · Method
How we work
Compute it, don’t look it up
Every position comes from an ephemeris at request time. No pre-baked tables, no rounded sun-sign approximations, no text written in advance and swapped around.
Say when we don’t know
No birth time means no Ascendant and no houses. We tell you that. The other option is to assume noon and hand you a chart that looks complete but is not.
Show the working
The method page lists the ephemeris, the ayanamsa, the timezone handling and the tests. Every chart links to its own JSON with the exact UTC instant we resolved.
Both traditions, honestly
Vedic and Western are the same sky counted from different zero points. We build both properly and never imply one is the real one.
03 · State of play
Where we stand today
Accuracy
≈1 arcminute
VSOP87 and Brown lunar theory
Bodies
12
Sun through Pluto, plus Rahu and Ketu
Calculators
18
All free, no account
Birth places
70k
Every Indian town, and world cities over 5,000
04 · Our limits
What we won’t do
This industry has a fear problem. A frightening reading followed by a paid remedy is a reliable business model and a bad thing to do to people. So, plainly:
- Sell remedies, gemstones or pujas to “fix” a bad reading.
- Put a percentage on relationship compatibility.
- Predict death, disease, pregnancy or the outcome of a medical decision.
- Invent testimonials, ratings or user counts we don’t have.
- Ask for your email before showing you your own chart.
05 · Known gaps
What we’re still missing
A site that asks you to trust its accuracy should be equally clear about its gaps:
- We do not publish festival and vrat dates. They change from region to region. They also change with whether your family counts a month from the new moon (amanta) or the full moon (purnimanta). One national answer would be wrong for most readers.
- Only the Lahiri ayanamsa is offered. Raman and KP practitioners are not served yet.
- Interpretation is thin. We compute far more than we currently explain.
- Shadbala is not computed — the six-fold strength score. The sixteen divisional charts and Ashtakavarga are in. The varshphal also leaves out the Sahams and the Tajika aspects.
06 · Sources
What this is built on
Two open datasets do the heavy lifting. We credit both here. Their licences ask for it, and you should be able to check our sources.
astronomy-engine
Planetary and lunar positions, from VSOP87 and Brown’s lunar theory. MIT licensed.
github.com/cosinekitty/astronomy →GeoNames
Birth places — 70,167 cities and towns with their coordinates and timezones, licensed CC BY 4.0.
geonames.org →
Judge it yourself
Read the method, then cast a chart and check it against whatever you already trust.