The left part already stands for sunrise and is a variant of the sunrise 旦, where the sun is above the horizon. When the moon 月 is still there, it is the morning. The sunset is: 莫.
Please be aware that this very similar radical 莫 stands for the sunset. This appears strange, but seems to be fact-based due to: sunset 暮 and morning 朝.
The radical tsuki stands for moon or month when used at the right side of a character. However the radical niku 肉 that stands for body or body-part is in many cases simplified to 月 and thus looks equal as "moon".
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