The head of Serpent Mound is aligned with the point on the western horizon where the sun sets on the Summer Solstice, the longest day of the year. Some believe the three main curves of the serpent's body point to the Summer Solstice sunrise, the Equinox sunrise, and the Winter Solstice sunrise. Others believe they align with the Minimum Northern Moonrise, where the moon rises at the midpoint in its cycle, and the Maximum Southern Moonrise. Because the mound's U-shaped curves have short sight lines and precise alignments cannot be clearly defined, it may not be possible to determine whether its builders intended it to align with the sun or the moon. Many earthworks built by the ancestors of contemporary American Indians align with horizon points marking key rising and setting points of the sun and moon, possibly linking these sacred sites to the rhythms of the cosmos or allowing them to serve as calendars.