as·tro·phys·ics
 /ˌæstrəˈfızıks/  noun   [  noncount  ]
  : the scientific study of the physical and chemical properties and structures of stars, planets, and other objects in outer space
  as·tro·phys·i·cal /ˌæstrəˈfızıkəl/  adj  
  as·tro·phys·i·cist /ˌæstrəˈfızəsıst/  noun  ,  pl   -cists [  count  ]