In J. R. R. Tolkien's legendarium, the Two Trees of Valinor provided light to the land of the Valar in the Elder Days. One of the trees, Laurelin, was gold and emitted a golden light, while the other one, Telperion, was silver and had silver light.
These two trees were destroyed by Melkor and Ungoliant, but two of the Valar were able to save Laurelin's last fruit and Telperion's last flower, which ultimately became the sun and the moon, respectively.
This design incorporates Laurelin's golden fruit as the center of the sun and Telperion's silver flower has the moon at its center.