First use of open cluster   Ive been trying to determine who coined the term open cluster but thus far I havent had much success It wasnt in use during the s when William Herschel put out his first catalogue of clusters in use Herschel himself used the expression irregular cluster The oldest confirmed use I could locate for open cluster was from an  publication That range would fit the time frame when John Herschel performed his early astronomy work However his General Catalogue of Nebulae and Clusters wasnt published until