I'm trying to make sense of the word 妖星 ("demon star") which I have encountered in a Japanese phrase. This word does not appear in any Japanese or Chinese (English) dictionaries I've run across, but searching for the word on Google turns up a number of hits in Chinese sites (especially https://baike.baidu.com/item/%E5%A6%96%E6%98%9F which appears to be a dictionary definition). However I don't speak/read Chinese, and auto-translations of that page (e.g. https://translate.google.com/translate?hl=en&sl=zh-CN&u=https://baike.baidu.com/item/%25E5%25A6%2596%25E6%2598%259F&prev=search) are such broken English all I can really tell is that it's an idiom that seems to reference Taoist astrology. What is the meaning of this term (both astrologically and idiomatically) - or at least enough information that I could look up more information on English reference sites (right now I don't even have a good enough English translation of the word to look it up on English sites)?
well, "妖星" is a category name of observable astronomical / meteorological phenomenons, those are assigned as "bad omen".
in the book "靈臺秘苑" by 庾季才, in volume 15, it was defined as:
roughly, means "evil star (妖星), the so called (者), [is] the rebels of (之變) five elements (五行), [and / or] five planets (五星), produced (生) by (所) the bad force (惡氣) from the sky and earth (天地)"
afterward, the author listed 40+ entries in this category "妖星", an interesting point is:
"彗星", "孛星" & "長星", comets; & "客星", nova; are also listed as "妖星"
i would suggest you find someone who can read literary chinese, and understand astrology / astronomy to help you. the google translate cannot handle literary chinese, the link provided is, . . . :(
last, the english book "stars of jade" by julius d w staal, would give you some basic ideas about "chinese astronomy".
have fun :)
妖星 can be found in, at least, two Chinese to English dictionaries:
star of evil omens; comet
unlucky stars (novae, comets, etc.)
and even one Chinese to French dictionary:
Étoile néfaste; comète.
There is the idea, that is popular is some astrological circles, that certain stars can have certain negative effects on people and their behavior. Comets, also, have been seen as bad omens in many cultures throughout history.