A: Distance estimates for many objects are just that - estimates. The values given in different sources can vary by quite a bit. We have made a determined effort to get information from the most authoritative sources.
A: If there is a galactic object that is left out, it is generally because the distance to it is unknown. For planetarium programs, the object can still be plotted without a distance. However, for Our Galaxy, when showing the position in 3D, the distance is crucial.
A: The data come from a variety of sources depending on the object type. Please see the built-in Help section on Data Sources for more detail.