A few days past the vernal equinox, yin and yang are in perfect balance. Hence: we see rainbows and lightning.
Liza Dalby, in her wonderful book East Wind Melts Ice, is great on this topic of yin and yang within the 72 micro-seasons 七十二候 of the ancient calendar.
According to ancient Chinese philosophy, the changing seasons were caused by the alternating movement of the two primal essences of yin and yang. In this system half the year is dominated by yin and half by yang. Dalby writes that “It is as if the living universe were slowly breathing a 180-day inhale of yin followed by an equally long exhale of yang.”
Don’t you love that?
It is only at the two equinoxes when the two forces are balanced in equal measure. Being balanced between male and female, yang and yin, things are generated. Things like lightening and rainbows. Thunder and lightning is associated with both autumnal and vernal equinoxes, while rainbows —like great serpents and dragons are generated around the spring equinox (unless you live in Hawaii, where they are around all year long!)
In Japan, rainbows are thought to be bridges joining earth and heaven. But in China, they have always been seen as dragons.
The “time when rainbows are visible” 虹始見 happens around 4/15.
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In haiku, which you cannot properly write without seasonal words called kigo 季語, both rainbows 虹 (niji) and thunder 雷 (kaminari) belong to summer . When thunder is accompanied with lightning, that is associated in poetry with autumn.
All your "lightening" instanced have a spurious 'e'.
I hope I see a rainbow! Thank you for featuring this vital lesson.