Galactic clusters;0; 
Galaxy;90; 
Galileo;160; 
Gamma radiation;253; 
Gaseous giants;342; 
Geocentric world-view;410; 
GHRS;495; 
Giant;591; 
Giotto;640; 
Globular cluster;711; 
Gravitation;802; 
Gravitational force;932; 
Gravitational lens;1005; 
Greenhouse effect;1077; 
H II region;1250; 
Halo;1294; 
Heliocentric world-view;1378; 
Hertzsprung-Russell diagram;1465; 
Horizon;1558; 
HSP;1633; 
HST;1725; 
Hubble space telescope;1902; 
Hubble;1841; 
Hubble's law;2002; 
Hydrogen;2054;