الأصناف الرئيسية
2X
الأقسام
الفروع
- 520Astronomy & allied sciences1
- 521Celestial mechanics
- 522Techniques, equipment & materials
- 523Specific celestial bodies & phenomena
- 524[Unassigned]
- 525Earth (Astronomical geography)
- 526Mathematical geography
- 527Celestial navigation
- 528Ephemerides
- 529Chronology