ceilometer an instrument for measuring by triangulation and recording the distance between the earth and the cloud ceiling. nephelognosy divination by the observation of clouds. nepheloscope an apparatus for expanding moist air to demonstrate the process of cloud formation. nephogram a photograph of clouds, taken with a nephograph. nephograph an instrument for photographing clouds and producing nephrograms. nephology the branch of meteorology that studies clouds. —nephologic, nephological, adj. —nephologist, n. nephophobia an abnormal fear of clouds. noctilucence the condition of being visible during the short summer nights, especially high-altitude clouds. —noctilucent adj. nubilation 1. the formation or arrangement of clouds. 2. the obscuration caused by clouds.