If there isn't a definitive (original)marker...does that indicate that upward or downward rolls can be watched by being in a right place at the right time (ie the viewer moving around the mound on any day to ensure the sunrise/set is in appropriate position)...anytime of the year, a movable feast if you will and unlike other constructs which only offer this event at solstice etc.....or does it only occur here at certain times of the year too?