Accuracy
Computed to the precision of a research observatory.
Every planet position on this site is computed in your browser's nearest Cloudflare edge in under 2 milliseconds, with the same ΔT correction NASA applies to eclipse predictions. We do not call an external API. We are the engine.
The accuracy envelope, body by body.
These are the documented precision bounds for every position we publish. They match Astrodienst's public calculator and are well inside the ±1° interpretive threshold that defines a "different sign" in tropical Western astrology.
| Body | Precision |
|---|---|
| Sun | ±0.01° |
| Moon | ±0.3° |
| Mercury | ±0.1° |
| Venus | ±0.1° |
| Mars | ±0.2° |
| Jupiter | ±0.1° |
| Saturn | ±0.1° |
| Uranus | ±0.1° |
| Neptune | ±0.1° |
| Pluto | ±0.2° |
| Ascendant | ±0.5° |
| Midheaven | ±0.5° |
Why ΔT (Delta-T) matters.
All Meeus astronomical formulas are expressed in Terrestrial Time (TT) — a uniform, atomic-clock-based timescale. Civil clocks run on Universal Time (UT), which tracks Earth's rotation. Earth's rotation is gradually slowing (tides, mantle drag), so the two timescales drift apart by a few seconds per century.
The difference, ΔT = TT − UT, sounds tiny. But the Moon moves ~0.0003° per second of TT. At ΔT = 69s (today), that's ~0.02° — enough to flip the Moon sign for someone born within ~4 minutes of a cusp.
| Birth year | ΔT |
|---|---|
| 1900 | -2.7s |
| 1950 | +29s |
| 1980 | +51s |
| 2000 | +63s |
| 2026 | +71s |
| 2050 | +93s |
We use NASA's Espenak & Meeus 2006 polynomial fit (the same model used by NASA eclipse predictions and Swiss Ephemeris), accurate to ±2 seconds within 1800–2150. The correction is applied automatically to every position we compute. Most consumer astrology apps do not do this.
How we compare — honestly.
We are not Swiss Ephemeris. Swiss Ephemeris is the research standard. We are, deliberately, the best edge-runtime implementation that runs in 2 ms with no commercial license. Here is the honest picture:
Swiss Ephemeris (research standard)
- Method
- JPL DE441 + Brown ELP-2000/82 lunar theory
- Moon precision
- ±0.0001°
- ΔT correction
- Yes
- Where it runs
- Local binary
CosmicPath (this site)
us- Method
- Meeus 1998 algorithms, VSOP87 truncated + Brown 4-term lunar
- Moon precision
- ±0.3°
- ΔT correction
- Yes — NASA Espenak & Meeus 2006 polynomial
- Where it runs
- Cloudflare edge, <2ms/chart
Typical consumer astrology app
- Method
- Often undisclosed; many use Sun + Moon only
- Moon precision
- ±1° to ±3°
- ΔT correction
- Usually no
- Where it runs
- Server-side, slow
Newspaper horoscope
- Method
- Sun sign only
- Moon precision
- Not computed
- ΔT correction
- N/A
- Where it runs
- N/A
- We do not claim research-grade ±0.0001° precision. That requires Swiss Ephemeris, a commercial license, and ~50MB of ephemeris data files — neither of which fits the edge runtime.
- We do not claim to know the exact second of your birth. Most birth certificates round to the nearest minute. Our Ascendant/Midheaven inherit that uncertainty.
- We do not claim every Moon sign is right at the cusp. If you were born within ~10 minutes of the Moon changing signs, you should verify against Swiss Ephemeris before any major decision.
- We do not claim sidereal/Vedic positions match Western tropical positions. Different system, different math. Both are honored, both have their own pages.
- We do not predict outcomes. Accuracy of position computation is separate from accuracy of interpretation. Position is math. Interpretation is editorial. We say so out loud.
Verify any claim on this page.
Every number above is reproducible. The engine source is in src/lib/astronomy.ts, the ΔT polynomial is in deltaTSeconds(), and the canonical references are Meeus 1998 (chapters 7, 22–25, 47) and NASA TP-2006-214141 (Espenak & Meeus).
If you find an error — a chart we computed wrong by more than the envelope above — email us. We will fix it that day and publish what changed. Read the full methodology →
Numbers are one kind of proof
Precision is measurable. The methodology, the ethics policy, and the public addresses for hard questions are how we are honest about everything that isn’t.
Methodology
The line between deterministic chart calculation and AI interpretation.
Ethics & safety
What we will and will not do, how we use AI, and crisis resources.
Our promise
Why we exist, who we are, and the lines we will not cross.
Our stance
How we hold the honest middle between fundamentalism and dismissal.
FAQ
Readings, privacy, payments, and the hard questions astrology gets weaponized around.
Sealed Letter
A once-a-year forecast composed from your actual chart. Free for members.
Contact
Support, privacy, security, press — five addresses, every reply written by a person.
Try a free snapshot
No signup, no card. The fastest way to see whether we mean any of this.
Free birth chart
Sun, Moon, Rising, all 10 planets — computed transparently.
Deep reports
Life Crossroads, Annual Forecast, and four more — written by the same engine.