| A | B |
|---|
| Ulcer | an open sore |
| Retrogade Motion was part | of the Copernicus Sun centered universe |
| Red Shift is part of the | Expanding Universe concept |
| Uranus | seventh planet from the Sun |
| Harold Urey | discovery of heavy hydrogen |
| Ulna the bone on the little | finger side of the forearm |
| Ultrasonic - a frequency above our | audibility limits |
| Ultra-violet -- wavelength | slightly shorter than that of visible light |
| Umbilical cord connects the | fetus with the placenta |
| Umbra | a shaded area |
| Undulate | move in waves |
| The Urethra carries off | urine from the bladder |
| Uric acid | a biological product |
| Ursa Major is the most | conspicuous constellation in the northern sky |
