• U-B color index
• U burst
• U, B, V magnitude
• UBV photometric system
• UBV-photometry
• UBV-ôîòîìåòðèÿ
• U Geminorum stars
• UK infrared telescope
• UK Schmidt telescope
• ultimate lines
• ultraviolet
• ultraviolet absorption
• ultraviolet astronomy
• ultraviolet data
• ultraviolet emission
• ultraviolet excess
• ultraviolet image
• ultraviolet light
• ultraviolet plate
• ultraviolet radiation
• ultraviolet range
• ultraviolet rays
• ultraviolet region
• ultraviolet spectrum
• ultra-wide angle eyepiece
• U-magnitude
• umbra
• U-measure
• unaided eye
• unbound electron
• uncertainty
• uncertainty of measurement
• uncertainty of observation
• uncertainty principle
• uncoupling
• under bad seeing
• under conditions of weightlessness
• underdeveloped
• underexposed
• underexposure
• under good seeing
• under observation
• under-sampling
• undisturbed
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• undisturbed photosphere
• undisturbed photospheric region
• undisturbed Sun
• undriven camera
• undulation
• uneven development
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