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Topocentric Ephemeris Study

A topocentric ephemeris study produces a table of positions as they would be observed from a specific point on the Earth's surface, rather than from the Earth's center. A topocentric study accounts for the observing location's longitude, latitude, and height, which is what makes it the right choice for observation planning.

The editor puts the study settings in a column on the left and the generated ephemeris table on the right.

A Topocentric Ephemeris Study whose ephemeris table holds Moon, Venus, Mars, and Jupiter sign columns for New York.

Create and Generate the Study​

To produce a topocentric ephemeris:

  1. Click Ephemerides → Topocentric Ephemeris on the menu bar.
  2. Configure the Basic Ephemeris Settings (Location, Zodiac, Ref. Plane).
  3. Configure the Ephemeris Date Range (Start Date, Start Time, End Date, Interval, Time Unit).
  4. Check the bodies you want in the Bodies list and the measurements you want in the Metrics list.
  5. Click the Run button beneath the ephemeris table.

A Topocentric Ephemeris Study with Mars, Jupiter, and Saturn checked in the Bodies list and an empty ephemeris table.

Step 1 is performed on the Ephemerides menu:

The Ephemerides menu with Topocentric Ephemeris highlighted between the Geocentric and Heliocentric Ephemeris entries.

An Interval of 1 with a Time Unit of Days gives one record per day.

caution

The location matters twice on a topocentric study. It fixes the observing point the positions are computed for, and it fixes the time zone each record is dated in. Make sure its latitude, longitude, and height are right in the Locations Editor before you generate.

Bodies​

A topocentric study offers the same 33-body Earth-frame catalog a geocentric study does, including the Diurnal Angles group: Ascendant, Medium Coeli, Descendant, and Imum Coeli. Here those angles are computed for the observing point you chose rather than for the Earth's center. See Bodies List.

Measurements​

Five body metrics are available for the table.

Ecliptic reference planeEquatorial reference planeWhat it reports
LongitudeRight AscThe body's position along the reference plane, in degrees.
Sign PositionSign PositionThe body's position expressed within its zodiac sign.
LatitudeDeclinationThe body's position perpendicular to the reference plane, in degrees.
DistanceDistanceThe body's distance, in AU.
SpeedSpeedThe body's rate of motion, in degrees per day.

After the Records Are Generated​

The study locks when the generation completes, and the Run button becomes invisible until you unlock the study. Meanwhile you can read, arrange, search, copy, and export the results: