[saraid216]

Ah. I grew up in a Cantonese-speaking Christian family in America, so I've never heard 星期天 used in speech at all.

Confusingly, the "seven luminaries" system in that article aren't just referencing the planets: they're also the names of Sun, Moon, Fire, Water, Wood, Metal, and Earth. I did get that sorted out by looking up Western alchemical ordering for the planets, which is in the same order. Wikipedia helpfully provides a table that includes the old names for the planets as well:

http://en.wikipedia.org/wiki/Classical_planet#East_Asia