Half-month

A half-month is a unit of time typically used in astronomy. Each month is separated into two parts:

  • days 1 to 15
  • day 16 until the end of the month.

Unidentified celestial objects, such as comets and asteroids, are given designations that contain the half-month as a letter of the English alphabet.[1][2] 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 directly from H (April 16–30) to J (May 1–15).

Half-month letters[1]
LetterDates
AJanuary 1–15
BJanuary 16–31
CFebruary 1–15
DFebruary 16–29
EMarch 1–15
FMarch 16–31
GApril 1–15
HApril 16–30
LetterDates
JMay 1–15
KMay 16–31
LJune 1–15
MJune 16–30
NJuly 1–15
OJuly 16–31
PAugust 1–15
QAugust 16–31
LetterDates
RSeptember 1–15
SSeptember 16–30
TOctober 1–15
UOctober 16–31
VNovember 1–15
WNovember 16–30
XDecember 1–15
YDecember 16–31

References
  1. "New- And Old-Style Minor Planet Designations". Minor Planet Center. Retrieved 17 December 2018.
  2. "Naming of Astronomical Objects". International Astronomical Union. Retrieved 17 December 2018.

See also
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