Geocentric Graphic Ephemeris Study
A geocentric graphic ephemeris study plots geocentric positions for the bodies you select as time-series curves rather than tabulating them. It shows the shape of planetary motion, turning points, crossings, and rates of change, which a table of numbers does not convey at a glance.
The study settings occupy a column on the left exactly as they do on a tabular ephemeris. The right side is an Ephemeris Graph instead of an ephemeris table.
Create and Generate the Study
To produce a geocentric graphic ephemeris:
- Click Ephemerides → Geocentric Graphic Ephemeris on the menu bar.
- Configure the Basic Ephemeris Settings (Location, Zodiac, Ref. Plane).
- Configure the Ephemeris Date Range (Start Date, Start Time, End Date, Interval, Time Unit).
- Check the bodies you want in the Bodies list and the metrics you want to plot in the Metrics list.
- Click the Run button beneath the graph.
Step 1 is performed on the Ephemerides menu:
An Interval of 1 with a Time Unit of Days gives one plotted sample per day.
A location is required even though geocentric positions do not depend on one. Cygnus calculates and displays each sample's date and time in the location's time zone. See Basic Ephemeris Settings.
Bodies
A geocentric graphic study offers the full 33-body Earth-frame catalog under all seven classification groups. Each body's curve is drawn in the color assigned to it in Graph Settings, so a plot with many bodies stays readable. See Bodies List.
Plotted Metrics
Only the four plottable metrics are offered. Sign Position has no graphic counterpart and is not in the list.
| Ecliptic reference plane | Equatorial reference plane | What it plots |
|---|---|---|
| Longitude | Right Asc | The body's position along the reference plane, in degrees. |
| Latitude | Declination | The body's position perpendicular to the reference plane, in degrees. |
| Distance | Distance | The body's distance, in AU. |
| Speed | Speed | The body's rate of motion, in degrees per day. |
Longitude is checked by default on a new graphic study. Each plotted metric gets its own value axis at the side of the plot.
After the Curves Are Plotted
The study locks when the generation completes, and the Run button becomes invisible until you unlock the study. The plot itself stays fully interactive:
- Show or hide a plotted metric. The plot redraws without generating the study again, because the generated series already carry all four metrics.
- Read a value off a curve.
- Adjust a value axis range.
- Pan and zoom the time window.
Changing which bodies are plotted does require unlocking and generating again.
A graphic study has no ephemeris table, so the Find and Export controls are hidden on it, and the count beneath the plot is labeled Point Count: rather than Record Count:. See Record Count.