This trio of words — inspired by the Summer Solstice — are completely unrelated historically, but their phonosemantics are remarkably similar.
Sun derives from Proto Indo European swen or suwen, a slightly modified version of the base form saewel, which meant both “sun” and “to shine”. Old English sunne was a feminine noun, and originally all references to the sun assumed that it was female (as in Tolkien’s Middle-Earth — and you may be sure that this was something Tolkien was quite aware of). The sun only became male in English in the 1500’s, long after the noun itself no longer had gender. Phonosemantically sun indicates powerful directed energy (”s”), narrowing toward a goal (”n”), but nevertheless suffused with relaxed, thoughtful qualities (short “u”). Perhaps this reflects the paradoxical power of the sun to both bake you in its heat and lull you to sleep on a golden afternoon.