| 释义 |
spiral arms spiral arms (spÿ -răl) See density-wave theory; galaxies; Galaxy; self-propagating star formation.spiral arms[′spī·rəl ′ärmz] (astronomy) The shape of sections of certain galaxies called spirals; these sections are two so-called arms composed of stars, dust, and gas extending from the center of the galaxy and coiled about it. |