/ Dictionary / Index A active sun: Meaning and Definition of Find definitions for: ac'tive sun' Pronunciation: [key] — Astron. Astron. the sun at a maximum of solar activity, occurring every 11 years. solar activity, superimposed on an unchanging background. Cf. quiet sun, solar cycle. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. active site active transport Related Content Daily Word Quiz: fresco Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language