[rah] 
| the 10th letter of the Arabic alphabet. |
[rah] | a sun god of Heliopolis, a universal creator worshiped throughout Egypt (typically represented as a hawk-headed man bearing on his head the solar disk and the uraeus). |
| regular army. |
| radium. |
| 1. | rear admiral. |
| 2. | Astronomy. right ascension. |
| 3. | royal academician. |
| 4. | Royal Academy. |
| Ra 1 (rä) n. Mythology The ancient Egyptian sun god, the supreme deity represented as a man with the head of a hawk crowned with a solar disk and uraeus. |
| Ra 2 The symbol for the element radium. |
| RA abbr.
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| ra·di·um (rā'dē-əm) n. Symbol Ra A rare, brilliant white, luminescent, highly radioactive metallic element found in very small amounts in uranium ores, having 13 isotopes with mass numbers between 213 and 230, of which radium 226 with a half-life of 1,622 years is the most common. It is used in cancer radiotherapy, as a neutron source for some research purposes, and as a constituent of luminescent paints. Atomic number 88; melting point 700°C; boiling point 1,737°C; valence 2. See Table at element. [Latin radius, ray + -ium.] |
| right ascension n. Abbr. RA The angular distance of a celestial body or point on the celestial sphere, measured eastward from the vernal equinox along the celestial equator to the hour circle of the body or point and expressed in degrees or hours. |
Ra
The symbol for the element radium.
| Ra
The symbol for radium. |
| radium (rā'dē-əm) Pronunciation Key
Symbol Ra A rare, bright-white, highly radioactive element of the alkaline-earth group. It occurs naturally in very small amounts in ores and minerals containing uranium, and it is naturally luminescent. Radium is used as a source of radon gas for the treatment of disease and as a neutron source for scientific research. Its most stable isotope is Ra 226 with a half-life of 1,622 years. Atomic number 88; melting point 700°C; boiling point 1,737°C; valence 2. See Periodic Table. |
| Ra radium |
RA
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