亢 is a picture of a person standing with their legs open, as in horse stance, and so holds the quality of strength that comes through a proper foundation.
This matches up with Chapter 8 of the Suwen, which says that the Kidney is in charge of strength and fortification.
The Kidney houses the Zhi, which is in charge of solid grounding in one’s life purpose.
Around the 5th Century BC, it is believed that eclipses would take place in this constellation.
This coming together of the Sun and the moon works as a symbol that points towards the ShaoYin relationship of the Kidney and Heart.