Our previous post shows the day of no-shadow when the sun over Honolulu on July 15, 2024 is directly overhead at the zenith (see photo on the left). There was a similar solar event on May 27, 2024.
Earlier, Iwakage reported on the dashed spotlight of May 21, 2024 at the Kanayama Megaliths (photo on the right). There is a corresponding observation of the dashed spotlight on July 21, 2024.
What do these two pairs of solar observations have to do with each other? Does this image from page 48 of the guidebook help?
Recall that the summer solstice occurs on the day when the earth’s obliquity (the tilt of earth’s axis of rotation) is most tilted toward the sun. The summer solstice is indicated in the circular calendar on 6/21. The dashed spotlight at Kanayama Megaliths first appears on 5/21 when the sun in the sky is at just the right angle that it shines on the bumpy surface of the triangular panel. Then the sun moves higher in the sky and does not produce a dashed spotlight. The dashed spotlight reappears on 7/15 and makes a last appearance on 7/22.
It is the same phenomenon as the zenith sun over Hawaii and other tropical locations. On May 27, the sun was at the zenith over Honolulu, on its way north (so to speak). After June 21, the sun “headed south” and passed over Honolulu on July 15.
In a manner similar to that used by the ancient astronomers of Kanayama Megaliths, the astronomers of Hawaii could also use the zenith sun observations for their calendar. By my personal experience in viewing both types of solar observations, I would say that the spotlight observation is the more accurate of the two. It is rather difficult to position a upright pole and then to note when there is no shadow. Besides, the dashed spotlight makes quite a show!
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Iwaya-Iwakage of Kanayama Megaliths 