??? ??? ??? astronomer [Definr]a physicist who studies stars and galaxy ??? ??? ??? galaxy [Definr]a collection of star systems, any of the billions of systems each having many stars and nebulae and dust ??? ??? ??? void [Definr]The ratio of the volume of void space to the volume of solid substance in any material consisting of void space and solid material, such as a soil sample, a sediment, or a