Ideogrammic compound (會意): 日(“sun”) + 月(“moon”) – the sun just rising and the moon not yet set – dawn (天明). Alternatively, it may be interpreted as two bright celestial bodies – bright. This form was already found in the oracle bone script and was prevalent throughout the eras.
Three other forms were found in the oracle bone script:
朙 < 囧(“window”) + 月 – the moon shining through a window – moonlight. This form was also prevalent in the ancient scripts and was considered to be the standard form in Shuowen. See this form's entry for its historical forms.
眀 < 目(“eye”) + 月 – bright eyes. This form was rarely attested, so it is still uncertain whether this form is actually equivalent to 明. It reappeared in the bamboo script of the Qin dynasty, but this was probably a corruption of 朙.