• 太陽たいよう — the sun
• 陽気ようき — cheerful / sunny weather
• 陽性ようせい — positive (test result, trait)
• 陽射ひざし — sunshine, rays of the sun
• 夕陽ゆうひ — sunset / evening sun

The left radical ⻖ (こざとへん) means hill or mound. The right side is 昜 (a form related to the sun and brightness). Together, 陽 originally referred to the sunny side of a hill — a metaphor for positivity and warmth. It’s also the “yang” in the yin-yang concept.