The plants 艹 are made by the sun 日 to be large 大 [= as long shadows] at sunset. - The very similar radical stands for sunrise. This seems bizarre, but can be argued based on the characters for morning 朝 in comparison to evening 暮.
This radical was developed from a circle with a central dot as the image of the sun. As you can hardly draw circles or dots with a brush, it became the current rectangular shape.
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stands for sunrise. This seems bizarre, but can be argued based on the characters for morning 
