A half-month is a unit of time typically used in astronomy. Each month is separated into two parts: * days 1–15, * day 16 until the end of the month. Unidentified celestial objects, such as comets and asteroids, are given designations that contains the half-month as a letter of the English alphabet. For example, an object seen in the second half of January would be identified with the letter B; if seen 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 from H (April 16-30) to J (May 1-15).