98.00.00 Stellar systems; interstellar medium; galactic and extragalactic objects and systems; the Universe
- 98.10.+z Stellar dynamics and kinematics
- 98.20.-d Stellar clusters and associations
- 98.35.-a Characteristics and properties of the Milky Way galaxy (1)
- 98.38.-j Interstellar medium (ISM) and nebulae in Milky Way (1)
- 98.52.-b Normal galaxies; extragalactic objects and systems (by type)
- 98.54.-h Quasars; active or peculiar galaxies, objects, and systems (9)
- 98.56.-p Local group; Magellanic Clouds
- 98.58.-w Interstellar medium (ISM) and nebulae in external galaxies
- 98.62.-g Characteristics and properties of external galaxies and extragalactic objects (for the Milky Way, see 98.35.-a) (1)
- 98.65.-r Galaxy groups, clusters, and superclusters; large scale structure of the Universe (1)
- 98.70.-f Unidentified sources of radiation outside the Solar System (2)
- 98.80.-k Cosmology (see also section 04 General relativity and gravitation; for origin and evolution of galaxies, see 98.62.Ai; for elementary particle and nuclear processes, see 95.30.Cq; for dark matter, see 95.35.+d; for dark energy, see 95.36.+x; for superclus (2)
- 98.90.+s Other topics on stellar systems; interstellar medium; galactic and extragalactic objects and systems; the Universe (restricted to new topics in section 98) (1)