Shabbos Bulletin Parshas Vaera 5779

When Chazal instituted to say Hallel on Yomim Tovim, Rosh Chodesh was not included. A minhag then developed to say Hallel on Rosh Chodesh as well; but in order to maintain the distinction between this Hallel and other, more technically obligatory ones, only half-Hallel is said.