Astronomy History 27 Physics 26 Periodicals 25 Early works to 1800 17 Observations 16 Popular works 15 Mathematics 12 Cosmology 10 Science 10 Observers' manuals 9 Astronomers 8 Stars 8 Dictionaries 7 Geophysics 7 Astronautics 5 Meteorology 5 Philosophy 4 Planets 4 Southern sky (Astronomy) 4 Study and teaching 4 Tables 4 Charts, diagrams, etc 3 Chemistry 3 Cosmogony 3 Data processing 3 Galaxies 3 History and criticism 3 Physicists 3 Problems, exercises, etc 3