Ephemeris Comparison Desk
Compare Sun, Moon and planet positions from two JPL models. Chart their differences and download the positions for your chosen time.
How do I compare two models of planet positions?
Choose the Sun, Moon or planets, two JPL models, and a time range. Set your viewing location and run the comparison. See how the positions differ on the chart and download both sets of values. A difference is not a measure of accuracy.
Your result
A little clarity, right here.
Start with your own content or load the example. Your result will appear here.
Three simple steps
How to use Ephemeris Comparison Desk
Choose Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune or Pluto.
Set the two ephemerides, timestamp, sampling and observer. Coordinates are ignored for Earth-center comparisons.
Run the service, compare the differences and download the complete report and positions.
Common questions
Good to know
Understand the result.
Keep the original.
Is this tool free, and are my files uploaded?
This tool is free with no account required. When you run the tool, your input goes to a separate processing service. Temporary files are deleted when the job ends. You can download the result to your device.
What are the limits and details?
Up to ten bodies and 2,000 target/time pairs over at most seven days, within 1900–2050 UTC. A zero-hour duration compares one instant. The final endpoint is always included; the preview shows 500 rows. Selectable bundled kernels are DE421 and DE440s; arbitrary kernel uploads and small-body orbits are unsupported. Differences between models are not absolute error estimates. Uses fixed NASA/JPL DE421 or DE440s data and Skyfield 1.55 bundled time tables, without runtime downloads. Sun, Moon, Mercury and Venus use body centers; Mars through Pluto use system barycenters. Positions include light travel time, aberration and gravitational deflection. Altitudes exclude refraction, terrain, weather and polar motion. Historical and future Earth-rotation uncertainty limits timing accuracy. Jobs stop after two minutes.