A historical ephemeris answers a narrow question: where was a solar-system body on a specified date, according to a defined astronomical model? To compare two printed tables, first check their timestamps and coordinate definitions. A difference of several hours can be material for the Moon; a different zodiac or ecliptic convention can shift every value.
| Input dates | 1800-01-01 through 2100-12-31, entered as proleptic Gregorian dates. This modern calendar convention is applied consistently across the range; a date copied from an old local record may require historical calendar research first. |
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| Time | UTC at the minute entered. A historical civil clock time should be converted to UTC with the offset that applied in that place on that date. The calculator does not infer old daylight-saving or local mean-time rules. |
| Centre | Geocentric, measured from Earth's centre. No birthplace is used, so it is not a topocentric horizon or house calculation. |
| Longitude | Apparent tropical longitude on the true ecliptic and equinox of date. Every 30° is labelled with a zodiac sign. |
Reading a comparison across decades
The optional second date puts two independently calculated positions side by side. Its angular gap is the shortest distance between their longitudes on a circle. If the Sun appears 10° apart on dates a year apart, the gap is 10° even though it travelled nearly a full circuit. The gap is a coordinate comparison, not a speed or total-distance measurement. The CSV preserves both numeric longitudes for further work.
Choosing a table or a chart
Use the monthly archive for consecutive noon-UTC daily rows from 2020 to 2036. Use the custom daily table for 7 to 90 consecutive dates. Use the exact historical explorer when the minute matters or dates are years apart. A natal chart requires an accurate birthplace, local birth time, and historical offset as additional inputs.
Precision and source
Table signs are rounded to the nearest arcminute. A result at a sign boundary can switch when the requested time changes slightly. CSV longitudes show six decimal places to avoid losing numbers during export; that format is not a promise of six-decimal-degree accuracy. The method is documented in the Astronomy Engine JavaScript reference. The U.S. Naval Observatory season service supplies an external solar-longitude boundary check for the focused tests.
What the positions mean
The calculator shows the Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto as viewed from the centre of Earth. The value is apparent geocentric longitude along the tropical true ecliptic of the chosen date. Zodiac signs are 30° labels on that 360° circle. This is a position table, without houses, birthplace, local horizon, or a personal reading.
The calculations use the locally bundled Astronomy Engine 2.1.19 GeoVector and Ecliptic functions. The selected UTC minute is used directly, rather than interpolating a noon table. The range is deliberately limited to 1800–2100; dates outside it have not been validated for this site. Its tables, data files, and layout are not used here.