Astronomy Among Ancient Tombs and Relics in Asuka, Japan

By Steve Renshaw and Saori Ihara

March, 1997

The Asuka area, south of Nara, is one of the most historically rich in Japan. Whether originating here or due to migration from Kyushu, the Asuka area became the center around which most of Japan united in early centuries of the "Christian Era". Reliable historical evidence indicates that exchanges between scholars of classic Chinese principles and the more aristocratic members of the Japanese court occurred as early as the mid 6th century. These exchanges not only gave rise to the infusion of technology, religion, and other aspects of Chinese culture, but astronomical calendar reckoning, astrology, and divination as well.

Unlike Kyoto and Nara, most of the towns in the Asuka area are rather small. There are many hills and small mountains with farms and assorted orchards mixed between. Among these, a visitor may find both remains of and intact kofun (tombs) of emperors and noblemen atop hills or high plateaus. From the perspective of archaeoastronomy, one of the most interesting of these is Takamatsu Zuka Kofun. While the exact date of construction is unknown, this tomb (discovered in 1972) provides one of the earliest and most interesting and definitive examples of Chinese/Korean astronomical influence on Japan in the 7th century. Paintings of the 28 sei shuku (moon stations) as well as the celestial Shibien surrounding the north star and remnants of three of the four "gods" of cardinal directions can be seen.

Several palaces (such as Fujiwara Kyo, Asuka Itabuki no Miya, and Kiyomi Hara no Miya) can also be seen in the Asuka area, and each of these seems to bear the same mark of Chinese influence mentioned earlier, a mark which was only gaining momentum in the prime of Japan's Asuka Era. While little reconstruction of these palaces has been completed, archaeological markers still provide the visitor with a sense of the importance of astronomical alignment in the early political affairs of Japan.

Dotted about the hills and small farms of the Asuka area are a number of stone relics and monuments, many of them shrouded in mystery relative to their date of construction and original function. Several of these have been the object of almost outlandish speculation, and a few have been associated with astrological or other "magical" rituals. Some may be of interest to archaeoastronomers for their possible Solstitial and/or Principle Term alignment. Two particular stones worth mentioning are Sakafune Ishi (literally "liquor ship rock") and Masuda Iwafune (Masuda was the name of a lake thought to have been near this stone; hence the translation would literally be "Masuda ship rock").

[Hill of Sakafune Ishi from Itabuki Site]
Sakafune Ishi is located on the top of the hill in the distance. The view is looking northeast from what is believed to be the palace of Asuka Itabuki no Miya

The function of Sakafune Ishi has long been the object of speculation, but some attempt has been made to give empirical weight to its use as an astronomical observation post. In the 1980 April/June issue of Archaeoastronomy, Kunitomo Sakurai reported the results of his studies related to the stone's position.

[Sakafune Ishi]
Looking west from the eastern edge of Sakafune Ishi. Bamboo covering on the hill prohibits siting to distant landmarks at the present time.

Sakurai claimed the central "trough" of Sakafune Ishi to be "well aligned along the true east-west direction, being coincident with the sun's path at the equinoxes". He made this assessment relative to celestial north which is about 7 degrees east of magnetic north in the Asuka area. He also measured the angles of the two outer "troughs" and found them both to be 29 degrees relative to the central "trough". Through triangulation and siting along the "troughs" toward distant mountain passes to the West, Sakurai concluded that the primary function of Sakafune Ishi was that of a sunset observing station for determining both winter and summer solstices. While mentioning similarity to structures in Korea, Sakurai also referred to a rather obscure passage in the Nihongi which has the emperor Temmu calling for construction of an astronomical observing "platform" (perhaps "stage") in 675 A.D. It should be noted that dates in the Nihongi are sometimes questionable, and there is, of course, no hard evidence that Temmu's "decision" referred to the construction of this particular rock. It cannot be doubted, however, that a tremendous amount of activity was ongoing in the latter part of the 7th century, and much of it had to do with Japanese scholars trying to build and develop their own tools for research.

While it is difficult to doubt the accuracy of Sakurai's alignments, a number of questions still remain relative to whether or not the stone was actually used for astronomical observation. Pottery found just to the east of the stone indicates that the area was at one time a garden. This, of course, does not mean that the rock could not have been used as an astronomical observation point. However, it is difficult to explain the additional round depressions and "troughs" which do not seem to have alignment properties at all. Officially (and in tourist guide descriptions of the rock), no mention is made of its possible astronomical function. Instead, the visitor is led to believe that the rock might have been the site of ancient "incantations", a mixing "tool" for liquor (from which the rock got its name), some sort of water conduit for the palace to the southwest (see picture above), or simply a garden fixture.

It appears that Sakurai's interpretation of Sakafune Ishi was made based on an assumption that the rock was positioned in such a way in ancient times as to make the central trough's direction "truly" east-west. Sakurai may also have relied more on mathematical triangulation rather than thorough investigation of the rock's present position. Kuniji Saitou, while agreeing with Sakurai's interpretation (given a true east-west direction) also provides a slightly different view based on his own investigations of Sakafune Ishi as well as Masuda Iwafune located some distance to the west. He claims that the angle of the central "trough" of Sakafune Ishi is actually some 13 degrees north relative to a due east-west line and also claims that this angle exactly parallels the ridge line of Masuda Iwafune . He believes that such parallelism is not mere coincidence, but rather the product of planning by ancient scholars to aid in the planting of the all important agricultural icon of Japan... rice.

[Masuda Iwafune]
Masuda Iwafune is located near the top of a hill just a few hundred meters west of Okadera Station. The ridge line (mentioned by Saitou) parallels the two square holes.

Saitou believes that Masuda Iwafune was constructed some time after Sakafune Ishi. In Saitou's view, the more important solar point for early Japanese agriculture was "spring doyou entry" which occurs 13 days after the sectional solar term Pure Brightness [15 degree increment from Spring Solstice; for a discussion of Principle and Sectional terms, see The Lunar Calendar in Japan]. Siting west along Masuda Iwafune 's ridge line, one could determine when the sun set at (not "Pure Brightness" itself), but the exact date of "Spring Doyou Entry". He further believes that Sakafune Ishi was later repositioned with its 13 degree offset to also site the sun's setting on this all important day.

Historically, there is some support for Saitou's speculations. Without a doubt, most every Japanese historian agrees that it was the arability of the Yamato plain and the ease with which "paddy" rice could be cultivated that formed a nucleus around which early rulers both obtained and maintained wealth and some sense of centralized power. "Paddy" rice is grown using a wet field method of agriculture, and "Spring Doyou Entry" was the signal, often accompanied by imperial ceremony, for beginning the agricultural season and taking "planting matters" into hand.

Officially, Masuda Iwafune , like Sakafune Ishi, is not recognized as an ancient astronomical observing station. Records from the Edo Era describe it as the base for a once large monument which commemorated the building of Masuda Lake nearby (now drained and part of Kashiwara City). Other speculation includes use of the rock for astrological incantation, and some historians believe it may simply be the remains of a tomb designed for two people of royal lineage.

Obviously, as with many alignment sites around the world, definitive evidence is still lacking with regard to these two stones' historical function. The same may also be said of other relics in the area. However, the Asuka region provides a wealth of historical material which may occupy the imagination of an archaeoastronomer and/or historian for days.

Readers interested in seeing pictures of other relics and learning more about the Asuka area should check the Asuka Museum Home Page.

Ancient Astronomy and Geomancy in Kyoto

Geomancy and Imperial Position in Nara


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Steven L. Renshaw

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