writing one sun 日 is quicker than 3 so it was simplified to 星 the question "Why _does_ the "star" must be the union of "sun" and "born, life"" is very similar to "why sister starts with s "

I think 星 is a 形声字 in which 生 only represents the pronunciation of 星 and therefore has nothing to do with the meaning of 星. The pronunciation of 生 is close to that of 星, though they are not exactly the same.

以下出自 沈括 夢溪筆談 卷二十　神奇 (隕石) 治平元年，常州日禺時，天有大聲如雷，乃一大星，幾如月，見於東南。少時而又震一聲，移著西南。又一震而墜在宜興縣民許氏園中。遠近皆見，火光赫然照天，許氏藩籬皆為所焚。是時火息，視地中有一竅如杯大，極深。下視之，星在其中，熒熒然。 良久漸暗，尚熱不可近。又久之，發其竅，深三尺餘，乃得一圓石，猶熱，其大如拳，一頭微銳，色如鐵，重亦如之。州守鄭伸得之，送潤州金山寺，至今匣藏，遊人到則發視。王無咎為之傳甚詳。 夢溪筆談 : http://zh.wikipedia.org/wiki/%E6%A2%A6%E6%BA%AA%E7%AC%94%E8%B0%88 沈括 : http://it.wikipedia.org/wiki/Shen_Kuo 這段話表示 1000年前中國人就已經將 "星墜為隕石 星為鐵 " 的天文和物理現象認識清楚了 (至於占星術仍然盛行) 星字的由來 有人將 生 解釋為聲符者 但看這裡 不喻而明 請看金文 http://www.chineseetymology.org/CharacterEtymology.aspx?submitButton1=Etymology&characterInput=%E6%98%9F

I have to say that though we may know how characters are evolved into what they look like today, even historians or archiologists probably would have no idea why ancient people choose this specific character to represent its meaning in the first place. We can only postulate, but we would never know the truth. As for "星", it is composed of three "日" above and one "生" below. "日" is an object in the sky. If there is only one object, it means the sun. If there are many they are the stars. Actually I wonder why “晶” desn't represent the stars. But ancient people give "晶" another meaning. Three suns must be very bright, so "晶" means bright. Back to "星", stars are very important to ancient Chinese. They observe stars and make prophecies. For example, the rising of a new star means a very important person was born. So stars are important to people's life. Actually, people say that every single star in the sky represents a person living on the earth. That's probably why they put "生" below. Stars and people are connected.