Use the same input and calculation settings when comparing tools. A difference is a reason to inspect those settings, not immediate proof that either entire product is wrong.
Download the demonstration result (JSON). It contains every value shown on this page: input, time conversion, settings, positions, angles, house cusps, aspects, fixed-star contacts.
A reproducible example
Use the example below to inspect the birth input, time conversion, calculated factors and comparison result. The values should be traceable to the recorded calculation.
Demonstration birth: 1991-09-06 at 18:30 local time, Kyiv, Ukraine (50.4501° N, 30.5234° E), Europe/Kyiv at UTC+3, so 1991-09-06 15:30 UTC. Tropical zodiac, Placidus houses, Swiss Ephemeris 2.10.03. Download the full result (JSON) or see how to verify it.
Input
| Field | Value |
|---|---|
| Date | 1991-09-06 |
| Local time | 18:30 |
| Time status | recorded (demonstration data) |
| Place | Kyiv, Ukraine |
| Coordinates | 50.4501° N, 30.5234° E |
Time conversion
| Step | Value |
|---|---|
| IANA time zone | Europe/Kyiv |
| Offset in force on that date | UTC+3 |
| Universal Time | 1991-09-06 15:30 UTC |
| Julian day (UT) | 2448506.145833 |
The offset is the one that applied in Kyiv, Ukraine on 1991-09-06, not the offset in force today. A tool that applies the current offset to a historical date can shift the Ascendant and every house cusp.
Settings
| Setting | Value |
|---|---|
| Engine | Swiss Ephemeris via the sweph Node binding |
| Library version | Swiss Ephemeris 2.10.03 (package ^2.10.3-b-1) |
| Ephemeris | Swiss Ephemeris data files (SEFLG_SWIEPH), speed flag on |
| Zodiac | tropical |
| House system | Placidus |
| Lunar node | true node |
| Lilith | osculating lunar apogee (Swiss Ephemeris body 13) |
| Part of Fortune | ASC + Moon - Sun, day and night alike |
| Natal aspect orbs | conjunction 8°, sextile 6°, square 8°, trine 8°, opposition 8°; the five major aspects only |
There is no house-system or zodiac switch in NatalChart.AI: every chart is tropical and Placidus. Applying and separating are not computed.
Positions
| Body | Longitude | Sign and degree | Speed | House |
|---|---|---|---|---|
| Sun | 163.5457° | 13°33′ Virgo | +0.9704°/day | 7 |
| Moon | 139.0225° | 19°01′ Leo | +14.5955°/day | 7 |
| Mercury | 145.6065° | 25°36′ Leo | +0.8358°/day | 7 |
| Venus | 141.9051° | 21°54′ Leo | -0.2674°/day (retrograde) | 7 |
| Mars | 183.4630° | 3°28′ Libra | +0.6468°/day | 7 |
| Jupiter | 148.8019° | 28°48′ Leo | +0.2150°/day | 7 |
| Saturn | 300.8444° | 0°51′ Aquarius | -0.0442°/day (retrograde) | 12 |
| Uranus | 279.9033° | 9°54′ Capricorn | -0.0106°/day (retrograde) | 11 |
| Neptune | 284.0918° | 14°06′ Capricorn | -0.0104°/day (retrograde) | 11 |
| Pluto | 228.0048° | 18°00′ Scorpio | +0.0218°/day | 8 |
| North Node (true) | 287.5725° | 17°34′ Capricorn | -0.0770°/day (retrograde) | 12 |
| Chiron | 125.2405° | 5°14′ Leo | +0.1009°/day | 6 |
| Lilith (osculating apogee) | 305.8121° | 5°49′ Aquarius | -1.1890°/day (retrograde) | 12 |
| Ceres | 221.0706° | 11°04′ Scorpio | +0.3541°/day | 8 |
| Pallas | 196.0369° | 16°02′ Libra | +0.4216°/day | 8 |
| Juno | 285.8222° | 15°49′ Capricorn | -0.0125°/day (retrograde) | 11 |
| Vesta | 132.9138° | 12°55′ Leo | +0.4329°/day | 6 |
Longitudes are geocentric, tropical, rounded to four decimals of a degree. Speed is the daily change in longitude; a negative value is retrograde motion.
Angles and points
| Point | Longitude | Sign and degree | House |
|---|---|---|---|
| Ascendant | 314.9898° | 14°59′ Aquarius | 1 (first cusp) |
| Midheaven | 249.8956° | 9°54′ Sagittarius | 10 (tenth cusp) |
| Vertex | 162.5751° | 12°35′ Virgo | 7 |
| Part of Fortune | 290.4666° | 20°28′ Capricorn | 12 |
Part of Fortune formula, day and night alike: Ascendant + Moon − Sun. With the values above: 314.9898° + 139.0225° − 163.5457° = 290.4666°, which is the stored value. A tool that uses the traditional night formula (Ascendant + Sun − Moon) for a birth after sunset will show a different point; that is a settings difference, not an error.
House cusps
| House | Cusp longitude | Sign and degree |
|---|---|---|
| 1 | 314.9898° | 14°59′ Aquarius |
| 2 | 13.7492° | 13°45′ Aries |
| 3 | 48.0551° | 18°03′ Taurus |
| 4 | 69.8956° | 9°54′ Gemini |
| 5 | 87.8914° | 27°53′ Gemini |
| 6 | 106.8959° | 16°54′ Cancer |
| 7 | 134.9898° | 14°59′ Leo |
| 8 | 193.7492° | 13°45′ Libra |
| 9 | 228.0551° | 18°03′ Scorpio |
| 10 | 249.8956° | 9°54′ Sagittarius |
| 11 | 267.8914° | 27°53′ Sagittarius |
| 12 | 286.8959° | 16°54′ Capricorn |
Aspects
The chart lists 49 major aspects among the 17 bodies. The ten tightest, with the rule each one passed:
| Pair | Aspect | Exact | Measured | Orb | Rule |
|---|---|---|---|---|---|
| Pallas and Juno | Square | 90° | 89.79° | 0.21° | within 8° |
| Pluto and North Node (true) | Sextile | 60° | 59.57° | 0.43° | within 6° |
| Sun and Neptune | Trine | 120° | 120.55° | 0.55° | within 8° |
| Chiron and Lilith (osculating apogee) | Opposition | 180° | 179.43° | 0.57° | within 8° |
| Moon and Pluto | Square | 90° | 88.98° | 1.02° | within 8° |
| Uranus and Ceres | Sextile | 60° | 58.83° | 1.17° | within 6° |
| North Node (true) and Pallas | Square | 90° | 91.54° | 1.54° | within 8° |
| Neptune and Juno | Conjunction | 0° | 1.73° | 1.73° | within 8° |
| North Node (true) and Juno | Conjunction | 0° | 1.75° | 1.75° | within 8° |
| Mars and Chiron | Sextile | 60° | 58.22° | 1.78° | within 6° |
An aspect is listed when the measured separation is within the orb for its type. Applying and separating are not computed, so a tool that labels them adds information this result does not carry. See how orbs work.
Comparison
Second tool: an independent calculation with Swiss Ephemeris 2.10.03 using the Moshier ephemeris, which needs no data files, for the same date, time, place, tropical zodiac and Placidus houses. Tolerance set for this page: 1′ of arc. Demonstration result generated on 2026-09-12 (UTC).
| Body | NatalChart.AI (ephemeris files) | Independent run (Moshier) | Difference |
|---|---|---|---|
| Sun | 13°32.74′ Virgo | 13°32.7′ Virgo | 0.04′ |
| Moon | 19°01.35′ Leo | 19°01.3′ Leo | 0.05′ |
| Mercury | 25°36.39′ Leo | 25°36.4′ Leo | 0.01′ |
| Ascendant | 14°59.39′ Aquarius | 14°59.4′ Aquarius | 0.01′ |
The largest difference is 0.05′: the values agree within 0.1′ of arc, well inside the 1′ tolerance. The remaining difference comes from the two ephemeris models (data files against the built-in analytical Moshier model) and from rounding the independent run to a tenth of an arcminute.
Note what this comparison is. Both runs use the same Swiss Ephemeris library, so they check settings and implementation: the time conversion, the coordinates, the zodiac, the house system and the point definitions. They are not two independent astronomical models.
Reproduction
- Download the demonstration result (JSON); it holds every value above.
- Enter the same date, time and place: 1991-09-06, 18:30, Kyiv, Ukraine (50.4501° N, 30.5234° E).
- Match the timezone offset: UTC+3, so 1991-09-06 15:30 UTC.
- Set the tropical zodiac.
- Set Placidus houses, the true node, Lilith as the osculating apogee and the Part of Fortune formula Ascendant + Moon − Sun.
- Compare the planets before the houses and the aspects.
Check it step by step
- Copy the example’s date, time and place into the comparison tool.
- Match the timezone conversion and coordinates as closely as the tools allow.
- Match the zodiac, house system and relevant point settings.
- Compare planetary positions before comparing houses and aspects.
- Inspect the published tolerance and the actual differences.
- If a result disagrees, check assumptions, rounding and any warnings before drawing a conclusion.
Do not compare a noon fallback with a known-time chart as if the inputs were identical.
What this establishes
A reproducible comparison checks the displayed calculations under stated conditions. Two interfaces using the same underlying ephemeris are a check of implementation and settings, not two fully independent astronomical models.
The comparison does not validate astrological predictions or make AI-generated explanations infallible. Those are different questions.
Report a discrepancy
Describe the settings and the affected calculation. Use the support contact for private information; do not post a personal birth record or private chart link publicly.
Questions
Why does another tool show a different Ascendant for the same birth?
Most often the entered time was converted with a different timezone offset, the coordinates differ, or the other tool uses a sidereal zodiac or another house system. Match those settings first, then compare the planets before the houses.
Does agreement between two tools prove the reading is right?
No. Agreement checks the calculated positions under the stated settings. The interpretation and any AI-generated explanation are separate questions and are not validated by a matching calculation.
Can I verify my own chart the same way?
Yes. Use your own date, time and place in a second tool with the same settings and follow the steps on this page. Keep your birth record private; the example here uses demonstration data only.
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