|Hi, I've just started learning Japanese with my Genki I textbook and am enjoying it! Does anyone know why the kanji "Moon" is used to for Monday, "Fire" for Tuesday, "Water" for Wednesday and so on? It puzzles me.. does it have any historic significance to it? Thanks!|
I'm not sure if this answer is correct but it seems to be true.
Tuesday: the day for "Tiu" (Mars) （火星「かせい」）→火曜日
Wednesday: the day for "Woden" (Mercury)（水星「すいせい」）→水曜日
Thursday: I have no idea
Friday: the day for "Frigg" (Venus)（金星「きんせい」）→金曜日
Saturday: the day for "Saturn"（土星「どせい」）→土曜日
I guess the name of the days in Japanese is basically based on the name of stars, which is same to English. I hope it helps you study Japanese.
Japanese wikipedia confirms Sawa's answer.
And Thursday comes from Jupiter, 木星（もくせい）.
Just for the records, in Japanese you can use the same word for star and planet, but maybe is not the same in English. I am not sure, as I am not native in any of them.