Solar Megaliths of Nakatsugawa
For twenty years Yoshiki Kobayashi and Shiho Tokuda have been researching how the Kanayama Megaliths of Gifu Prefecture determine a well-developed solar calendar from Jomon times. Since March 2018, they have been carrying out an investigation into the Funaiwa and other megaliths in the region of Maruyama Jinja in Nakatsugawa City, Gifu Prefecture, which is south-east of Kanayama (in Gero City). There seems to be a connection with the Kanayama Megaliths’ Jomon observational solar calendar system.
In this post and the next one, we explain some exciting new findings that were reported by Kobayashi and Tokuda in the journal paper cited below. Part 3 of this series will be a photo gallery posted on the JIN blogsite.
The Funaiwa Megalith is a fish-shaped megalith found on the site of the Maruyama Jinja shrine in Nakatsugawa City. It is on the southern side of a small 330m hill. Funaiwa has a length 12m, height 6m, width 8m, carved out of one piece of granite (Fig. 12). It is likened to a funa (crucian carp); however, there are no local explanations about it. It sits on a pedestal stone, as impressive as a whale. There are other megaliths on top of the hill, behind the shrine which faces west. Although Maruyama is by no means a tall mountain, nevertheless due to the flatness of the surrounding terrain there is a broad view all around it.
Equinox Observations at Maruyama Jinja
The megaliths of Maruyama Jinja are arranged east-west (Fig. 13). Looking at Funaiwa from the south, the head is facing west, the tail fin east. Below the head, the belly of the fish sits on the pedestal, with a 3m deep cut oriented due west. Furthermore, part of the pedestal has a space for observation. From inside this space, one looks at the distant mountains in the west. The sun can be seen on spring and autumn equinoxes setting over Mount Kasagiyama. Kasagiyama is around 12km away at the border of Nakatsugawa. In Fig. 14 (left) is the observation space, and (right) is the view from the space. Fig. 15 shows the photos taken on spring and autumn equinoxes from that space; the time of sunset on spring equinox is 17:50. It seems clear that Funaiwa was constructed to receive the light from the equinox sun setting over Kasagiyama.
As the upper part of Fig. 13 shows, sunrise can be viewed at the two megaliths which face east behind Maruyama Jinja. There is a crack between the two megaliths into which the meridian sun will penetrate on spring and autumn equinoxes. From the wedge-shaped opening between the two megaliths, sunrise can be viewed during the entire year. The extreme northern sunrise occurs at summer solstice, from a direction 30 degrees north of east. The extreme southern sunrise occurs at winter solstice, from a direction 30 degrees south of east. However, this type of viewing is not very accurate for determining the solstice directions and the equinox direction.
The investigators asked themselves how the east-west directions for the equinoxes were accurately known at the megaliths of Maruyama Jinja. Please continue to Part 2 of this series.
Data from: “The Kanayama Megaliths and Funa Iwa Solar Observation System of Gifu Prefecture,” Y. Kobayashi and S. Tokuda, J. Astro. Archaeol. Soc. Japan, Vol. 1, No. 1, 1-9, 2019. Figures and an advance copy of the paper were graciously provided by S. Tokuda.