Available topics


This service accepts several user inputs and returns an ephemeris for a single time, along with a graphic depiction of the region of uncertainty for the observation.

The user inputs include the date and time of the observation in UTC, the Minor Planet Center observatory code (500 is for no parallax correction), and the sigma level for the uncertainty region. Deciding the appropriate value for sigma is not easy, and it depends strongly on the error statistics for the object in question, which are generally not gaussian. As a general rule a choice in the range 3.0-4.0 will give a region which is large enough to include the object (with "reasonably" high probability).

The output is, for the most part, self-explanatory. Our software intelligently decides whether to plot a line of variations or an uncertainty region, and also whether or not to include nonlinear effects. The results of these decisions are always written on the screen.

It is important to note that you can make a request that will take a few minutes to compute. It would be quite unusual, but it is possible to submit a request that takes more than the timeout period for your browser (typically 4 minutes), so you will see a browser warning indicating the form returned no data. Also note that if the object has an extremely poor orbit (e.g., uncertainty in semi-major axis ~> 0.3 au) then the output from this service may be quite unusable. If you have troubles from either of these problems, you can use the OrbFit software package to precisely control the parameters of these plots.

The reference system used is J2000 Equatorial.