Spring equinox

春分，二月中。分者，半也；此當九十日之半，故謂之分，秋同義；夏冬不言分者，蓋天地間二氣而已。方氏曰：「陽生於子，終於午，至卯而中分，故春為陽中。」而仲月之節為春分，正陰陽適中，故晝夜無長短雲。

This is how Wu Cheng describes spring equinox. His 月令七十二候集解 is a very interesting book about solar terms written in Yuan Dynasty. I found this book last year when compiling solar term (節氣)-related articles at English and Classical Chinese editions of Wikipedias. According to this book, 穀雨 is actually pronounced as gǔ yù, and 芒種 should be pronounced as máng zhǒng. The character 雨 when pronouncing as the fourth tone (去聲) acts as the verb form of rain. A dictionary explains more on this topic.

According to the JPL Horizons On-Line Ephemeris System, the spring equinox this year will take place at 2007-03-21 00:07:26 UTC.