Topocentric Ephemeris Study
A topocentric ephemeris study generates a tabular listing of planetary positions as observed from a specific location on Earth's surface. Unlike geocentric coordinates (measured from Earth's center), topocentric coordinates account for the observer's actual position, introducing parallax corrections. This is especially significant for nearby bodies like the Moon.
Creating a Topocentric Ephemeris Study
- Click the Topocentric Ephemeris toolbar button or select Ephemerides > Topocentric Ephemeris from the menu.
A new study appears in the studies list panel and the study content area shows its configuration. The coordinate origin is fixed to Topocentric.
Configuring the Study
The configuration parameters are identical to the Geocentric Ephemeris Study, including study name, location, zodiac system, reference plane, date range, interval, body selection, and metric selection.
The selected location is especially important for topocentric ephemerides because it determines both the time zone for date/time display and the observer's geographic position used for parallax calculations.
Zodiac System
Select a zodiac system from the Zodiac System dropdown:
| Option | Description |
|---|---|
| Tropical | Based on the vernal equinox |
| Sidereal | Based on fixed star positions |
Reference Plane
Select a reference plane from the Reference Plane dropdown:
| Option | Description |
|---|---|
| Ecliptic | Positions measured relative to the ecliptic plane |
| Equatorial | Positions measured relative to the celestial equator |
Time Unit
Select the interval time unit from the Time Unit dropdown:
| Option |
|---|
| Hours |
| Days |
| Months |
| Years |
Available Bodies
The topocentric ephemeris study includes the same bodies as the geocentric study:
| Body | Type |
|---|---|
| Moon | Planet |
| Mercury | Planet |
| Venus | Planet |
| Sun | Planet |
| Mars | Planet |
| Jupiter | Planet |
| Saturn | Planet |
| Uranus | Planet |
| Neptune | Planet |
| Pluto | Planet |
| Tenet | Smaller Body |
| Lunar Apogee | Lunar Axis |
| Mean Apogee | Lunar Axis |
| North Node | Lunar Axis |
| Mean Node | Lunar Axis |
| Vesta | Smaller Body |
| Juno | Smaller Body |
| Ceres | Smaller Body |
| Pallas | Smaller Body |
| Chiron | Smaller Body |
| Pholus | Smaller Body |
Generating the Ephemeris
After configuring all parameters, click the Run button to generate the ephemeris. See Generate Ephemeris Records for details.