EXAMPLES OF ANCIENT SOLAR OBSERVATORIES
The following are only a few examples of the different types of ancient solar observatories.
SITES BASED ON ELEVATION OBSERVATIONS
A small chapel adjacent to the Sphinx in Egypt has a hole in the ceiling with a straight edge, aligned in the direction of the path of the sun across the sky, which casts a shadow on the floor. The position of this shadow changes with the elevation of the sun in the sky, allowing a mark to be made at the sun's high point each day. Although this may have been used to determine the solstices, its primary use was probably to determine the spring equinox.
SITES BASED ON AZIMUTH OBSERVATIONS
Stonehenge in England has a "heel stone" which has a slanted edge such that when observed from within the circle of stones the sun is just barely visible along that edge as the sun rises on the day of the summer solstice. Machu Pichu has a similar slanted object, a nearby mountain. By this method, several minutes are available for observation as contrasted with observations made on a flat horizon.
Newgrange in Ireland uses a long tunnel into the side of a hill to shadow out all light except for a very narrow slice from the bottom edge of the sun at sunrise on the winter solstice. (The opening is large enough that it may use both elevation and azimuth effects.)
Some of these sites are more accurate than others. (Newgrange determines a solar period of 5 days - with possible interpretation of the shadow on the back wall to a more precise date.)
Click here to see a list of ancient solar observatory sites.