The Archaeogeodesy of the Miami Circle.

Possible Evidence of Astronomical and Geodetic Knowledge in Prehistoric Florida.

1999 by James Q. Jacobs. All Rights Reserved.

A recently discovered monument, the Miami River Circle, in Miami, Florida, may represent the best evidence of precise ancient astronomical knowledge in the United States. The prehistoric monument may also soon be destroyed to make way for a building. The discovery of a circle carved into the bedrock near the mouth of the Miami River in Florida has attracted the attention of the archaeological world and the national media. The prehistoric monument was recently found on private property. It was also about to be destroyed as part of a construction project. Efforts continue to prevent its destruction.

I hope this article will raise, and perhaps answer, some questions about the astronomical knowledge of the ancient Americans. In 1992 I coined the term "archaeogeodesy" to encompass the study of ancient navigation, point positioning and place determination, and ancient and prehistoric understandings and representations of the size and shape of the earth. For a more complete definition and discussion of archaeogeodesy see my series of articles entitled Archaeogeodesy, A Key to Prehistory. My archaeogeodesy study involved other Florida monuments (earthworks and earthen and shell mounds) before the discovery of the Miami Circle. Naturally I was curious about the relationship of the Miami Circle to these and other monuments and to the geoid. My study of the archaeogeodesy of the Miami Circle has produced a possible rationale for its location at the mouth of the Miami River as well as a possible means of precisely dating the construction.


What I found most significant about the monument is its latitude, particularly with respect to the geometry of solar illumination. At the Miami Circle latitude the angle between the summer and winter solstice rise/set positions expressed fundamental astronomical relationships during the prehistoric era. I will review the basic astronomy needed to understand these relationship first, and then present findings. If you need a more complete discussion of the related astronomy than that which follows see the Archaeogeodesy articles.

The earth's axis of rotation in inclined in relation to the earth's plane of orbit around the sun. This is referred to as the Obliquity of the Ecliptic (OB). The obliquity produces the seasons, which Floridians experience as the sun rising in the east-northeast at midsummer and the east-southeast at midwinter. At the equator the angle on the horizon between the solstice and equinox sunrises equals the obliquity angle. As one moves away from the equator that angle increases as a trigonometric function of latitude. The present day latitude at the Miami Circle is 25.7686 degrees. Latitude changes only a few inches a year due to secular polar motion. The obliquity angle changes over time, producing a significant change in the angle of solar illumination. Today obliquity is about 23.44 degrees while two millennia ago it was about 23.70 degrees. To find the level horizon angle of solar rise/set, obliquity of the epoch is divided by the cosine of the latitude. Twice this amount is the angle between the winter and summer solstice rise/set positions. Herein my calculations assume a level horizon and the center of the sun. The calculations are not the actual positions of the solar orb, but rather a fundamental calculation to arrive at such.

The following graphic illustrates the approximate sunrise view at the Miami Circle latitude.

The solstice angle viewed from Miami Circle expresses the relationship of two, and possibly all three, of the fundamental cosmic motions. These motions are earth's axial rotation, earth's revolution around the sun, and the orbit of the moon around the earth. The following graphic illustrates the amount of lunar motion per rotation and per day and presents an equivalent code. For computational simplicity I created the code to represent the relationships. (These and other values and astronomical constants, along with the code, are presented in my Astronomical Constants Index and other pages linked therefrom.) The cosmic motion relationships have a very slight change in rate over time. The amounts below are for Jan. 1, 0 hr., 2000 A.D. The temporal formulas for the calculations used herein and for other motions are found on the Astronomy Formulas pages.

The fundamental cosmic motions the solstice angle at Miami Circle expresses are in the form of multiples of the lunar motion angles illustrated here.

For the epoch 1700 B.P. the angle between the Miami Circle winter and summer solstice rise/set positions (calculation is obliquity / latitude cosine) was four times the lunar motion angle (R27). Because of the temporal change in solar illumination angle, both the amount of lunar orbit per earth rotation (R27) and the mean daily lunar motion angle (C27) have been expressed at the Miami Circle latitude during different prehistoric epochs in this fundamental calculation. The angle was four times mean daily lunar motion (C27) around 2200 B.P. and four times the angle of lunar motion per earth rotation (R27) around 1700 B.P. The latitude today where this same angle equals 4.0 R27 is about an eight of a degree north of Miami Circle (about 9 miles).

The relationship of Miami Circle to other Florida monuments was also considered. Crystal River Shell Mound, the largest shell mound in the world, is located 3.14 degrees north of Miami Circle at a distance equal to one thirtieth the earth's diameter. The distance to Big Mound equals one one-hundredth the earth's diameter. This area of inquiry was not as fruitful. Of course, the Miami Circle is a unique monument and there is little expectation of any relationships to large earthen or shell works.


If the Miami Circle was constructed due to the astronomical relationships cited herein then the two dates, 2200 B.P. and 1700 B.P., are probable construction dates. Of course, it is possible that both these dates were significant during the history of the monument. If the above discussed relationships are in fact the rationale for the location of the Miami Circle, the monument is a singular discovery and may represent unique evidence of ancient astronomical knowledge in the United States. Also, the most significant aspect of the monument would be the fact that it is located precisely where it is. Perhaps these findings will be useful in further investigation of the monument and in understanding of its details.


It has often been the case in the Americas that the monuments and artifacts of Native American cultures are destroyed before they are studied or understood. The burning of the Mayan codices epitomizes this scenario. The ignorant European invaders burned almost every Mayan book. From the three surviving Mayan codices significant astronomical information has recently been deciphered. Codices once perceived as works of a false religion, and therefore deserving of destruction, are now known to be scientifically valuable books evidencing the most advanced astronomical knowledge of that epoch. Many of the large geometrical earthworks of the Ohio Valley have been destroyed. Dams have inundated much of the rock art in the United States. Archaeological sites on private property have no legal protections, unless they are burials. Landowners in the United States can destroy archaeological materials if they wish.

I hope this brief article will cause the reader to consider several questions. Is the true nature of the Miami Circle understood by those who would destroy it, or by any of us? Are we even able to understand the meaning and significance of the Miami Circle? Or are we like the invading Spaniards in their search for gold, ignorant of the scientific importance of artifacts of other cultures? Will we only know the full significance of Miami Circle after discovering other yet unknown monuments and their interrelationships? Is the Miami Circle a unique monument or part of a complex of monuments?

Have Euroamerican priorities changed in the last five centuries? Have we gained any respect for the cultures and peoples whose lands were stolen? Will the near destruction of the Miami Circle serve to raise awareness of the level of culture and the intellectual achievements of the ancient inhabitants of La Florida and the other conquered lands of the New World? The Miami Circle is a microcosm that will answer these questions one more time. Perhaps, for once, a prehistoric monument will be preserved rather than destroyed. Are we willing to sacrifice the Miami Circle for just another Miami skyscraper?

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