English 'sun' and Spanish 'sol' are estranged cousins — both from PIE *sóh₂wl̥, yet Germanic and Latin carried them so far apart the kinship vanishes on the ear. Chinese sidesteps naming: 太阳 means 'great yang,' placing the sun on a cosmic axis with its shadow-twin 陰. Esperanto takes the Germanic syllable and appends -o — the most economical act of naming in this set. That all four reach past the bare object, through lineage, cosmology, or deliberate craft, suggests the sun has always demanded context.
Old English 'sunne' was a feminine noun; the modern form shed the final vowel by the Middle English period. Cognate with German 'Sonne', Dutch 'zon', Gothic 'sunnō'.
'Sol' doubles in Spanish as a solfège note (G), the Peruvian currency, and a common given name — its reach extends well beyond astronomy.
大 depicts a standing person spreading both arms — a body claiming space, signifying magnitude. The added dot (丶) tips 'great' into 'extreme' or 'too much,' as if sheer bigness needed a small overflow mark to become superlative.
The traditional 陽 showed the sunny side of a hill: the mound radical (阜, written 阝) beside 昜, an archaic element depicting a rising, radiating sun. Simplified to 阳, the character retains hill (阝) beside sun (日) — the image of light falling on elevated ground, the warm south-facing slope that defined 'yang' long before it became a philosophical term.
日 (rì) is the classical and literary word for 'sun' (also 'day'), preserved in compounds: 日本 (Japan, 'sun-origin'), 日食 (solar eclipse). 太阳 is the standard vernacular term in modern Mandarin.
Productive derivations: suna (solar, adj.), sunlumo (sunlight, lit. sun-light), sunleviĝo (sunrise, lit. sun-rising), sunobrilo (sunshine, lit. sun-gleam). 'sun-' is one of the few Esperanto content roots drawn primarily from Germanic rather than Romance sources.
Perhaps the sun is the one thing every language must name — and yet none of these four can quite resist reaching for something else to say it.