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Pulkovo NEO Page

Central Astronomical Observatory at Pulkovo Official Site

Central Astronomical Observatory at Pulkovo
of Russian Academy of Sciences, St.-Petersburg, Russia


General InformationGeneral Information


Occultations of Stars by AsteroidsOccultations of Stars by Asteroids

Ephemeris SupportEphemeris Support

Apparent close Approaches to the StarsApparent close Approaches to the Stars

Estimation of Accuracy of the ObservationsEstimation of Accuracy of the Observations





The estimation of accuracy of the current CCD observations of asteroids and comets is constantly performed at Pulkovo Observatory. The observations evidently have the errors, sometimes very significant. The (O-C) values, so called "Observed" minus "Calculated" positions, characterize numerically the observations of any observatory, both professional and amateur, during a short period (one or several close nights). Each (O-C) value includes the errors of the theory of object's motion plus the random and systematical errors of observations. The numbered asteroids with long observational history usually have good theory of motion. So the (O-C) values for these objects nearly entirely define the errors of observations.

The (O-C) values may differ significantly for various objects but their mean errors show a reliability of "Atmosphere + Telescope + CCD camera + Catalog" system at mean observational conditions. These values can be considered as an indicator of accuracy of the CCD positional observations with given telescope. For reliable estimation of the accuracy of observations we usually consider from ten to twenty (or more) various numbered asteroids observed during several nights per month (more then 50 positions). When there are three or more positions of an object per night we can calculate the "internal" accuracy (a symbol "int" in the Tables). For several close nights we derive the "external" accuracy (a symbol "ext" in the Tables). A difference between "int" and "ext" estimations may be explained by an influence of the reference star positions used for astrometric reduction.

It is to be noted that the EPOS software package can get the (O-C) values not only for positions but for angular velocities also. This option helps in sure identification of object. So every EPOS user can control his own observations before their sending to MPC and compare their accuracy with the values of other observers.