Astronomy dictionary – W Browse through our astronomy dictionary to find definitions for some of the most common terms used in practical astronomy and space science. Click on one of the letters below to search for a term. a b c d e f g h i j k l m n o p q r s t u v w x y z Ww Waning When the phase (illumination) of a planet or moon’s disc is decreasing in size. For example: ‘A waning crescent Moon can be seen tonight’. Waxing Moon Phases of the lunar cycle when the face of the Moon appears to be getting larger each day. In the waning parts of the lunar cycle, the face of the Moon appears to be getting smaller. White dwarf A small and dense type of star formed at the end of a star’s life if it has a mass less than the Chandrasekhar limit, which is about 3 x 10^30 kg.