Half-month


The half-month is a calendar subdivision used in astronomy. Each calendar month is separated into two parts:
  • days 1 to 15
  • day 16 until the end of the month.
Newly identified small Solar System bodies, such as comets and asteroids, are given systematic designations that contain the half-month encoded as a letter of the English alphabet. For example, an object discovered in the second half of January would be identified with the letter B; if found in the first half of February, the letter would be C. The letter I is not used, to prevent confusion with the number 1. Instead, the letters proceed directly from H to J. The letter appears in the provisional designation, then when the object is confirmed the letter is incorporated into the comet designation or minor planet designation.