Subject
- planetary nebulae25
- radio astronomy25
- x-ray sources23
- apparent magnitude22
- young stellar objects22
- stellar spectral types20
- astronomical object identification19
- interstellar medium19
- line intensities18
- carbon stars17
- early-type stars17
- morgan-keenan classification16
- effective temperature15
- radio sources15
- molecular clouds14
- ob stars14
- astronomical models13
- be stars13
- hst photometry13
- late-type stars13
