U ma - upsi
- U magnitude
- UBV photometry
- UBVGRI photometry
- UBVRI photometry
- UBVRIJKL photometry
- UCBV photometry
- ultra short period B stars
- ultra short period variable stars
- ultraviolet
- ultraviolet astronomy
- ultraviolet background
- ultraviolet cameras
- ultraviolet colors
- ultraviolet continuum
- ultraviolet detectors
- ultraviolet excess stars
- ultraviolet extinction
- ultraviolet filters
- ultraviolet light
- ultraviolet lines
- ultraviolet luminosity
- ultraviolet objects
- ultraviolet photography
- ultraviolet photometry
- ultraviolet radiation
- ultraviolet sources
- ultraviolet spectrographs
- ultraviolet surveys
- ultraviolet telescopes
- umbra
- underlying
- units
- universal time
- universe
- unsharp masking
- unstable stars
- upper atmosphere
