Notes and Limitations


A few things to keep in mind:

  • GV by default assumes uses the equatorial radius for all bodies. This should be accurate for most calculations, except (e.g.) computing high-resolution timing of stellar occultations. For these cases, use the Wireframe Surface Style mode for high accuracy. This mode uses the proper triaxial ellipsoid shape for all bodies, and properly accounts for foreshortening.
  • GV is slow plotting zoomed-in planetary/satellite images. Zooming in to 0.05 deg for Jupiter C/A, for instance, may take 15 seconds or so to render. To speed things up, consider plotting only using Wireframe mode, which is very fast.
  • Planetary positions are computed by SPICE. They are highly accurate. If there is a discrepancy in positions between (e.g.) GV and STK, be sure the same SPICE kernel files are used. Click on List Kernel Info? to have GV display this information.
  • The Rectangular projection display uses a cartesian projection system. When looking near the celestial pole, fewer stars will be shown per square degree. GV properly adjusts for this cos(dec) term. A byproduct of this projection, however, is that planetary bodies appear 'squished' when looking at them from higher latitudes. The squishing introduces small errors in limb position for large bodies when viewed from the pole; however, the Wireframe Surface Style option uses high-precision calculations that adjusts for this effect properly.
  • In the Rectangular projection mode, GV's assume that bodies are at infinity -- that is, 180 deg of longitude and latitude are always visible. This is a fine assumption for the vast majority of observations. When this is not the case (e.g., orbital missions), use the Spherical mode, which removes these limitations.
  • Latitudes/longitudes are planetographic. When comparing to other tools, be sure to compare the same coordinates. For instance, the PDS Rings Node Jupiter Viewer uses planetocentric, while JPL's Horizons uses planetographic.
  • GV doesn't calculate shadows between bodies (e.g., shadow of Io on Jupiter, or shadow of Saturn's rings, on Saturn).
  • GV uses light-time corrections: that is, the plot corresponds to what at observer at the specified UTC time and position would observe. No correction is made for stellar aberration, which is a relativistic effect causing slight positional shifts in observed bodies for v/c >0. Typically this shift is <0.01 deg, and it affects planets and stars equally -- thus, it causes a small change in the absolute position of two bodies, but a much smaller change in their relative position. GV could be upgraded to properly account for this if desired; please inquire. (From a SPICE standpoint, GV uses abcorr = LT, not abcorr = LT+S.)