It's a Summer Solstice Celebration!
Colman Smith may have been inspired by and picked up some of the attributes of the three dancers from the story of Cancer, a giant crab who guarded Poseidon's daughters, the sea nymphs. With this being a water sign, the three dancers celebrate what appears to be a burgeoning, no doubt well irrigated crop with a cup of wine or two. It symbolizes all that is beautiful and kind about agriculture. We should recall that the first astrologers, the Egyptians, depended on the annual flooding of the Nile which began in the southern part of Egypt around early to mid June. More here.