The act of maintaining a bro-like persona via the intake of sunlight.* This can be witnessed on Beaches and college campuses across the United states. (note: also possible around fires, at Dave Matthews concerts, etc.) Specifically occurs with men ages 18-24, "chill" (see chill) outside in small groups, or "crews". (note: sunglasses, vintage tees, sandals, and Abercrombie and Fitch paraphenalia are key indicators of brotosynthesis.) Common, less scientific, synonyms include but are not limited to the following: chillin', hangin, livin' the dream.
verb: brotosynthesize

*Recent studies indicate that the intake of cheap beer may aid in this process; it has not yet been confirmed.