Man if you really want to trace the etymology of Chinese characters it gets to be a really long and crazy affair. You inadvertently stumbled across a thorny example.

The history of 晴 indicates pretty clearly that 青 is meant to be a phonetic compound rather than a semantic one, but it's not obvious how that came about.

晴 originated as the character 夝 and originally meant a clear night with visible stars after the rain has stopped (夝 is a 形声字 where 夕 means dusk or night and 生 is the phonetic compound) rather than a clear day. By focusing on the stars, we got alternate "spellings" of 暒 (which is a cross between using 星 phonetically and semantically) and 精 (borrowing its connotation of brightness). Gradually this focus on stars became a focus on brightness while maintaining the original "clearness." The latter character 精 then kept its phonetic component 青 and got a new semantic component 日 to distinguish itself from 精 and that's how we got 晴.

That's fascinating!

Doesn't that mean it's 青 that's the phonetic part? It means blue. blue day certainly is a fitting compound meaning regardless of its origin. On the other hand, no idea why moon and that radical (life?) = blue so that part is phontic?

> Doesn't that mean it's 青 that's the phonetic part?

I'm confused. That's indeed what I said and what the article states and what the original parent comment stated.

> On the other hand, no idea why moon and that radical (life?) = blue so that part is phontic?

That's not quite the direct evidence that 青 is phonetic rather than semantic. It's because already in 精 青 is not a semantic component but rather a phonetic one. In particular 精 was being used to describe clear, sunny days before the existence of 晴. Its semantic compound was then replaced with 日 to disambiguate this new meaning of 精 [0]. So the jump from 精 to 晴 is treating 青 as a phonetic component as well.

[0] "Replaced with" indicates an intentionality that may or may not have actually occurred. We don't have any records of someone literally coming out and saying "yeah I think 精 has too many meanings, I'm going to replace one of them with 晴." It's plausible that what may have occurred is the independent growth of a variant character 晴 that occurred after the rise of 精 that eventually supplanted 精. Regardless the existence of 精 is a pretty clear signal that it was the phonetic quality of 青 that was being used.

亜米利加 America, is where 米国 comes from (it couldn't be abbreviated as 亜 because that would have been confusing with e.g. 亜細亜 (Asia)).

I think the somewhat confusing thing here is that Japanese can pronounce the same kanji in different ways, from 'purely local Japanese' to variants of old Chinese pronunciation.

米国 "beikoku" sounds like a strange choice for "America". But then in 亜米利加 it's pronounced "mei", which does indeed explain the choice better.

Chinese use 美 'mei' for America and so 美国 'meiguo' is the US.

According to Kenneth G. Henshall, who wrote a book on the etymology of Kanji [1], it is quite common to choose a phonetic part that lend itself to the meaning of the word and not just a sound.

[1] https://www.amazon.com/Guide-Remembering-Japanese-Characters...