Sun is an interesting character, as well… it looks like a window (handy) but how did this character evolve to look like something that, lets face it, doesn’t look like a sun at all.
As I have said many times before, Chinese has evolved over thousands of years and just like English has ‘old English’, ‘middle English’ and ‘modern English’ so does Chinese.
In the Oracle Bone Script (c.1400BCE) the character for sun was a circle with a dot in the middle. It was a pictographic representation of the sun: http://bit.ly/1irEUnj
…but then it changed.
During the Seal Script (c.220BCE) the character evolved and became more rectangular. It almost looks similar to a goat’s eye (Google it, a goat has rectangular pupils). http://bit.ly/17l5cmy
As time progressed this character became more angular and geometric until the middle dot finally stretched to reach both side of the circle, and the circle became a rectangle!
So on to alternative meanings:
日 can refer to the sun (that big burning ball in the sky)
日 can also refer to day (when the sun is in the sky)
日 can also finally refer to a date/period, or day of the month.
Spring Time: 春日 [spring + date] (chun1 ri4)
Birthday: 生日 [life + day] (sheng1 ri4)
The common way to write sun (as in the solar object) is 太陽 [trad] or 太阳 [simp]. You can see the sun radical in the simplified form of the phrase.
太阳/太陽: too big + sun = [literally] big sun (tai4, yang2)
A word of warning though! The character 陽/阳 can also mean “male genitals” when it is used as a noun, so be careful!!!!!!
日 as noun: sun, day, date
日 as an adjective: Japanese
3. 生日快乐：Happy Birthday!