With what astronomical event might the great serpent mound be associated

Halley's Comet Pass

Explanation:

For centuries comets were considered messengers from the heavens that announced bad news.

Ancestral civilizations have fed myths about comets for years. In the earliest known mythology, the epic of Gilgamesh, the Babylonian king who lived around 2,600 BC, speaks of the arrival of a comet that caused the skies to burn with fire, the air to be impregnated with sulfur and earth sank.

In the fifteenth century, the reading by the priests of the Aztec empire of a comet predicted the return of the vengeful god Quetzalcóatl, represented by a great feathered serpent. The inhabitants of ancient Mexico identified him with the arrival of the ships of the Spanish conqueror Hernán Cortéz.