Sunday is the first day of a week , so it is No 1. (the boss), but No 1 has been given to 星期一 ， according the rules, Tuesday is 星期二 and so on.... Sunday should be called 星期七， and of course it is not proper to call the boss NO .7 , so we have to think another honorablename for 星期天。。。then people think a lot according what Bear234 explained above...more information for you , we also call Sunday 星期日 (日means 天），it is more often used in oral Chinese.

I basically agree with bear234 and you on your double qi theory...sounds reasonable...I also found something else, and I found it very reasonable. A week has 7 days, from Monday to Sunday and then Monday again...you can see that Sunday can be seen both as the end and beginning of this cycle. Therefore, if we use xingqi qi, it can only indicates the 7th day of a week (the end); the meaning (beginning part) Sunday carries cannot be shown in xingqi qi...so the general term "Tian (day)" would be a good choice. In ancient China, Japan and Korea, they also used the "7 days cycle" system, so it was a happy incident with the western system^^ Our ancestors use "Sun-Day" "Moon-Day" "Fire-Day" "Water-Day" "Wood-Day" "Earth/Soil-Day" then "Sun-Day" again(I guess this is related to 五行“the Five Elements") http://zh.wikipedia.org/wiki/%E6%98%9F%E6%9C%9F We started to use "xingqi yi/er/san...." from the beginning of 20th (around 1905). The emperor at that time set a bureau related to translation works.

Hello Garrett, I agree with you. do you know what when we say phone numbers we don't speak 1 as " yi " ? We speak "yao" for "1" instead. I guess it is also because something like this . To avoid confusing "yi" and "qi " . 1 and 7. My phone number is 15280.... = Yao wu er ba ling ...

I agree "the day to go to church" is the original