What is the meaning of 妖星? 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&amp;sl=zh-CN&amp;u=https://baike.baidu.com/item/%25E5%25A6%2596%25E6%2598%259F&amp;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:

靈臺秘苑　卷十三⋯卷十五　page 195


  妖星者﹒五行五星之變﹒天地惡氣之所生也


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" &amp; "長星", comets;  &amp; "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 :)