Sunrise or sun up is the instant at which the upper edge of the sun appears over the eastern horizon in the morning. The term can also refer to the entire process of the Sun crossing the horizon and its accompanying atmospheric effects.
Most people know that the Sun "rises in the east and sets in the west". However, most people don't realize that is a generalization. Actually, the Sun only rises due east and sets due west on 2 days of the year -- the spring and fall equinoxes! On other days, the Sun rises either north or south of "due east" and sets north or south of "due west.
Each day the rising and setting points change slightly. At the summer solstice, the Sun rises as far to the northeast as it ever does, and sets as far to the northwest. Every day after that, the Sun rises a tiny bit further south.
At the fall equinox, the Sun rises due east and sets due west. It continues on it's journey southward until, at the winter solstice, the Sun rises are far to the south as it ever does, and sets as far to the southwest.
Many, if not most, prehistoric cultures tracked these rising and settings points with great detail. If they had jagged mountains along the horizon, the exact points could be readily remembered. Without a suitably interesting horizon, standing stones could be arranged to line up with the various rising and setting points. Or, tree poles could replace the standing stones. Or, rock cairns could be used.
