The stone covered mound in the second picture aligns with an opening in the earthworks beyond through which the sun appears on the day of Winter Solstice.

There is a readable image of that sign in the first picture here. The second picture looks over the coils of the serpent, some of which retained a little snow, from near the museum. Some claims about the alignment of various parts of the serpent's body with the cosmos are at least a little uncertain. Even the apparent alignment of the head with the Summer Solstice sunset is not ironclad but it sure seems reasonable. The third and fourth pictures show that alignment from and toward the head.

I finished my walk around just in time to join a walking tour led by Bill Kennedy, the Site Director of both Serpent Mound and Fort Ancient. I did not recognize Bill at first but could see that he was the same fellow I'd seen at Fort Ancient at sunrise once he was ten feet away with people between us. The stone marker beside Bill can be read here. The presentation was excellent.