Sun and moon disc seats
In tantric iconography the sun disc and moon disc are the customary seats for both buddhas and yidams. The sun symbolizes jnana, or wisdom, while the moon is a symbol of bodhichitta, or compassion. [1]
And:
...the sandwiched union of the sun and moon discs represents the Vajrayana as symbols of conjoined wisdom and compassion.....the sun disc is like a fiery lens which ripens the sprout of enlightenment; the moon disc like a frosted crystal lens which cools with its white rays of compassion. [2]