Provisional designation in astronomy

Provisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery. The provisional designation is usually superseded by a permanent designation once a reliable orbit has been calculated. Approximately 47% of the more than 1,100,000 known minor planets remain provisionally designated, as hundreds of thousands have been discovered in the last two decades. TOC The current system of provisional designation of minor planets (asteroids, centaurs and trans-Neptunian objects) has been in place since 1925. It superseded several previous conventions, each of which was in turn rendered obsolete by the increasing numbers of minor planet discoveries. A modern or new-style provisional designation consists of the year of discovery, followed by two letters and, possibly, a suffixed number. For example, the provisional designation stands for the 3910th body identified during 1–15 March 2016: 2016 – the first element indicates the year of discovery. E – the first letter indicates the half-month of the object's discovery within that year and ranges from A (first half of January) to Y (second half of December), while the letters I and Z are not used (see table below). The first half is always the 1st through to the 15th of the month, regardless of the numbers of days in the second "half". Thus, E indicates the period from March 1 to 15. K156 – the second letter and a numerical suffix indicate the order of discovery within that half-month. The first 25 discoveries of the half-month only receive a letter (A to Z) without a suffix, while the letter I is not used (to avoid potential confusions with the digit 1). Because modern techniques typically yield hundreds if not thousands of discoveries per half-month, the subscript number is appended to indicate the number of times that the letters from A to Z have cycled through. The suffix 156 indicates 156 completed cycles (156 cycles × 25 letters = 3900), while K is the 10th position in the current cycle.