Guayabo Sky Map Stone

I had a passive interest in archaeology and archaeoastronomy, but a strange stone at the Guayabo National Monument in Costa Rica sparked my interest. --Michael O'Reilly F.

Illustrations

(Fig.1): Conception of the southern sky as it might have looked to residents of the country's largest pre-Columbian city 500 years ago.
(Fig.2): Photograph of the stone when it was used as a paving stone in the walkway that surrounds the central mound.
(Fig.3): Modern day map of the region of sky below the -60° latitude.
(Fig.4): Ancient map of the region of sky below the -60° latitude.
(Fig.5): Part of sky not visible to the observer +10° north of the equator.
(Fig.6): Rainfall 1979-61
(Fig.7): Green area indicates cloud cover over the mountains.
(Fig.8): The stone displayed with the rectangular coordinate system showing cloud cover over the southern mountains during May to October.
(Fig.9): How cloud cover builds up during the rainy season obscuring the sky behind them.

During the late 1970's my family and I lived in a second floor apartment in Moravia Costa Rica. Moravia is a small and quiet town northeast of San Jose. A nice thing about this apartment was the small balcony that we shared with my neighbor on the second floor. From this balcony we had a spectacular view of the southern sky adorned with a high rim of mountains that mark the southern boundary of the central valley. Eventually I was able to buy a used reflector telescope and amateur astronomy quickly became my hobby. Over the years I came to know the southern sky, partly because the northern sky was blocked from view on the balcony and partly because the area near the celestial south pole is full of interesting objects to observe. Not even the glare from the city lights could obscure the star clouds and with the help of a telescope, they were splendid. The position of these objects became burned into my memory after many years of observing this particular area of the sky.

-MAP SHOWING LOCATION OF GUAYABO NATIONAL MONUMENT- Early in 1975, my family and I decided to pack a picnic lunch and drive up to the Guayabo National Monument. The park is well known for its natural beauty and is the largest remnant of the indian civilization in Costa Rica. The indians who lived here were called Huetares. They lived in this area until the Spaniards came. The park is deep in the forest about half way up the southern slope of Turrialba volcano. The ancient indian city is just now beginning to be uncovered. In 1975 it was estimated that only 3% of the complex had been uncovered.

The dominant feature of Guayabo National Monument is the central mound which is a mound buttressed with a round stone wall. In all directions there are smaller mounds, stone walkways, streets and holding ponds for water. In all areas of the park you can see stone carvings. These stone carvings are random lines that wander all over the surface of the rocks. There is one stone however that is quite different from the rest. In 1975, this 1 1/2 foot diameter stone was located at the south or southeast side of the central mound imbedded in the stone walkway that surrounds the central mound. On a trip to Guababo in 1994, I discovered that this area was now closed to the public and the stone had been removed. A park ranger showed me the stone that was stored in a trailer on the park grounds. He told me that a mould was to be made of is so that a copy could be place in the walkway where the original once rested.

-VIEW OF THE SOUTHERN SKY AS IT APPEARED 500 YEARS AGO-
(Fig.1) Conception of the southern sky as it might have looked to residents of the country's largest pre-Columbian city 500 years ago. The central mound is on the right.
RETURN TO FIG. 5

During this trip, the first time I saw the stone I aimed my camera at it, focused and decided not to take a picture because it really was not very impressive and it would be a waste of film. After wandering around the park I later returned and looked down at the stone again. After a moment it all came clear and I could not believe what I was seeing. The image of the southern sky and this stone merged into one image in my head. Naturally I took a picture, many pictures and that same day worked in my makeshift darkroom so that I could compare the images with my star maps.

-PHOTOGRAPH OF THE STONE- (Fig. 2) Photograph of the stone when it was used as a paving stone in the walkway that surrounds the central mound.

Before I reveal what I feel is the startling meaning of this stone, I will first talk about other things that will make the meaning clearer.

Our galaxy in which we live is a flat disc shaped cloud of stars, we live on the outer limits of this disc but within the central plain of the galactic disc. When we look parallel or into this disc in the night sky we see a multitude of stars, stars so distant but dense that they appear to be a luminous cloud arching across the sky, this is the milky way. Now if we were to look away from the plain of the galaxy, the night sky will appear less populated with stars and darker.

We will now concern ourselves with a small portion of the sky, -90° (the south pole) to -60° latitude (the southern cross falls along this -60° latitude). Within this -60° latitude we find many interesting non stellar objects. From the vantage point of Costa Rica approximately +10° north of the equator looking due south in December, with a clear horizon we can see the Large Magellanic cloud. In the October night sky a little further down on the horizon we can see the Small Magellanic Cloud. They were both reported and used for navigation by Magellan in 1519. These two objects are of particular interest because they are the nearest external aggregation of stars nearest to the Milky Way galaxy. Although the clouds are considerably smaller than our galaxy and do not exhibit spiral structure, they are however separate galaxies. Now if we look south in April we will find the sky quite different because we are looking into the disc of the galaxy and we see the luminous cloud called the Milky Way but within this luminous cloud of stars is a dark spot called the Coal Sack. This dark object lies within the constellation Crux along with the Southern Cross. This dark spot in the Milky Way is due to a large cloud of obscuring matter that hides the myriad of stars lying beyond.

If we look at the southern sky in March along the -60° latitude we find two other interesting objects, a star cloud in the constellation Centaurs and NCG 3372 or the Keyhole Nebula in Carina.

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