(che - acti
- (chemical) yield
- A dwarf stars
- A giant stars
- A stars
- A subdwarf stars
- A subgian stars
- A supergiant stars
- AB variable stars
- Abell clusters
- aberration
- ablation
- abnormal spectra
- absolute intensity
- absolute magnitude
- absolute temperature scale
- absorption nebulae
- absorptivity
- absortion
- absortion coefficient
