Astrometric in the context of Observations of small Solar System bodies

The following is a list of unnumbered minor planets in chronological order of their principal provisional designation. Contrary to their numbered counterparts, unnumbered minor planets have a poorly determined orbit due to insufficient observational data. This also includes lost minor planets which have not been observed for many years, or even decades. As of August 2023, the Minor Planet Center (MPC) accounts for 676,755 unnumbered minor planets which represent 52% of the overall minor planet population. Unnumbered minor planets can be further divided into 129,103 single-opposition objects with short observation arcs, prone to mismatch and loss, and 547,652 objects that have been observed multiple times during opposition, when astrometric conditions are most favorable. The JPL Small-Body Database gives a running total of 676,786 unnumbered minor planets.

The tables below contain 115 objects with a principal designation assigned between 1927 and 1994. Additional partial lists cover the period from 1995 to 2004. Unnumbered minor planets detected after 2004 are not listed due to their large number. The orbital uncertainty parameter (U) ranges from low ("0") to very high ("9"). For some single-opposition objects no numeric uncertainty is given ("–"), with "E" indicating an estimated, rather than determined orbital eccentricity. Furthermore, a color code is used to indicate a body's basic dynamical classification, with additional information given in columns "class" and "description and notes" (especially for near-Earth objects, Jupiter trojans and distant objects). If available, mean diameters are taken from the latest NEOWISE publication, or, if not available, estimated based on an object's absolute magnitude and displayed in italics.

Stellar triangulation is a method of geodesy and of its subdiscipline space geodesy used to measure Earth's geometric shape. Stars were first used for this purpose by the Finnish astronomer Yrjö Väisälä in 1959, who made astrometric photographs of the night sky at two stations together with a lighted balloon probe between them.

Even this first step showed the potential of the method, as Väisälä got the azimuth between Helsinki and Turku (a distance of 150 km) with an accuracy of 1″. Soon the method was successfully tested by ballistic rockets and for some special satellites.

A critical-list minor planet (critical list numbered object or critical object) is a numbered minor planet for which existing measurements of the orbit and position are especially in need of improvement.

The IAU's Minor Planet Center (MPC) regularly publishes a list of these critical objects in their Minor Planet Electronic Circular. The list typically contains asteroids that have been observed at a small number of apparitions, especially on opposition, or that have not been adequately observed for more than 10 years, while other observatories create their own, customized lists. The MPC also lists currently observable critical objects on their website, providing differently formatted lists of orbital elements to the worldwide astrometric community.